Built-in Functions

The Python interpreter has a number of functions and types built into it that are always available. They are listed here in alphabetical order.

+---------------------------------------------------------------------------------------------------+ | Built-in Functions | +=========================+=======================+=======================+=========================+ | | A | | E | | L | | R | | | abs | | enumerate{.interpreted-text role="func"} | | len | | range()_ | | | all | | eval | | list()_ | | repr | | | any{.interpreted-text role="func"} | | exec | | locals | | reversed | | | ascii | | | | | | round | | | | | F | | M | | | | | B | | filter | | map | | S | | | bin | | float{.interpreted-text role="func"} | | max | | set()_ | | | bool | | format | | memoryview()_ | | setattr | | | breakpoint | | frozenset()_ | | min | | slice{.interpreted-text role="func"} | | | bytearray()_ | | | | | | sorted | | | bytes()_ | | G | | N | | staticmethod | | | | | getattr | | next | | str()_ | | | C | | globals | | | | sum | | | callable | | | | O | | super | | | chr{.interpreted-text role="func"} | | H | | object | | | | | classmethod | | hasattr | | oct{.interpreted-text role="func"} | | T | | | compile{.interpreted-text role="func"} | | hash | | open | | tuple()_ | | | complex | | help{.interpreted-text role="func"} | | ord | | type | | | | | hex | | | | | | | D | | | | P | | V | | | delattr | | I | | pow | | vars | | | dict()_ | | id | | print{.interpreted-text role="func"} | | | | | dir | | input | | property | | Z | | | divmod | | int{.interpreted-text role="func"} | | | | zip | | | | | isinstance | | | | | | | | | issubclass | | | | _ | | | | | iter | | | | __import__ | +-------------------------+-----------------------+-----------------------+-------------------------+

::: {.function} abs(x)

Return the absolute value of a number. The argument may be an integer, a floating point number, or an object implementing __abs__. If the argument is a complex number, its magnitude is returned. :::

::: {.function} all(iterable)

Return True if all elements of the iterable are true (or if the iterable is empty). Equivalent to:

def all(iterable):
    for element in iterable:
        if not element:
            return False
    return True

:::

::: {.function} any(iterable)

Return True if any element of the iterable is true. If the iterable is empty, return False. Equivalent to:

def any(iterable):
    for element in iterable:
        if element:
            return True
    return False

:::

::: {.function} ascii(object)

As repr, return a string containing a printable representation of an object, but escape the non-ASCII characters in the string returned by repr{.interpreted-text role="func"} using \x, \u or \U escapes. This generates a string similar to that returned by repr in Python 2. :::

::: {.function} bin(x)

Convert an integer number to a binary string prefixed with \"0b\". The result is a valid Python expression. If x is not a Python int object, it has to define an __index__ method that returns an integer. Some examples:

>>> bin(3) \'0b11\' >>> bin(-10) \'-0b1010\'

If prefix \"0b\" is desired or not, you can use either of the following ways.

>>> format(14, \'#b\'), format(14, \'b\') (\'0b1110\', \'1110\') >>> f\'{14:#b}\', f\'{14:b}\' (\'0b1110\', \'1110\')

See also format for more information. :::

::: {.bool([x])} Return a Boolean value, i.e. one of True or False. x is converted using the standard truth testing procedure <truth>{.interpreted-text role="ref"}. If x is false or omitted, this returns False; otherwise it returns True. The bool class is a subclass of int (see typesnumeric). It cannot be subclassed further. Its only instances are False and True (see bltin-boolean-values).

::: {.index} pair: Boolean; type :::

::: {.versionchanged} 3.7 x is now a positional-only parameter. ::: :::

::: {.function} breakpoint(args,*kws)

This function drops you into the debugger at the call site. Specifically, it calls sys.breakpointhook{.interpreted-text role="func"}, passing args and kws straight through. By default, sys.breakpointhook() calls pdb.set_trace(){.interpreted-text role="func"} expecting no arguments. In this case, it is purely a convenience function so you don\'t have to explicitly import pdb or type as much code to enter the debugger. However, sys.breakpointhook can be set to some other function and breakpoint{.interpreted-text role="func"} will automatically call that, allowing you to drop into the debugger of choice.

::: {.audit-event} builtins.breakpoint breakpointhook breakpoint :::

::: {.versionadded} 3.7 :::

Return a new array of bytes. The bytearray{.interpreted-text role="class"} class is a mutable sequence of integers in the range 0 \<= x \< 256. It has most of the usual methods of mutable sequences, described in typesseq-mutable, as well as most methods that the bytes type has, see bytes-methods.

The optional source parameter can be used to initialize the array in a few different ways:

If it is a string, you must also give the encoding (and optionally, errors) parameters; bytearray{.interpreted-text role="func"} then converts the string to bytes using str.encode.
If it is an integer, the array will have that size and will be initialized with null bytes.
If it is an object conforming to the buffer interface <bufferobjects>, a read-only buffer of the object will be used to initialize the bytes array.
If it is an iterable, it must be an iterable of integers in the range 0 <= x < 256, which are used as the initial contents of the array.

Without an argument, an array of size 0 is created.

See also binaryseq and typebytearray.

Return a new \"bytes\" object, which is an immutable sequence of integers in the range 0 <= x < 256. bytes{.interpreted-text role="class"} is an immutable version of bytearray{.interpreted-text role="class"} -- it has the same non-mutating methods and the same indexing and slicing behavior.

Accordingly, constructor arguments are interpreted as for bytearray.

Bytes objects can also be created with literals, see strings.

See also binaryseq, typebytes, and bytes-methods. :::

::: {.function} callable(object)

Return True if the object argument appears callable, False if not. If this returns True, it is still possible that a call fails, but if it is False, calling object will never succeed. Note that classes are callable (calling a class returns a new instance); instances are callable if their class has a __call__ method.

::: {.versionadded} 3.2 This function was first removed in Python 3.0 and then brought back in Python 3.2. ::: :::

::: {.function} chr(i)

Return the string representing a character whose Unicode code point is the integer i. For example, chr(97) returns the string 'a', while chr(8364) returns the string '€'. This is the inverse of ord.

The valid range for the argument is from 0 through 1,114,111 (0x10FFFF in base 16). ValueError will be raised if i is outside that range. :::

::: {.decorator} classmethod

Transform a method into a class method.

A class method receives the class as implicit first argument, just like an instance method receives the instance. To declare a class method, use this idiom:

class C:
    @classmethod
    def f(cls, arg1, arg2, ...): ...

The @classmethod form is a function decorator{.interpreted-text role="term"} -- see function for details.

A class method can be called either on the class (such as C.f()) or on an instance (such as C().f()). The instance is ignored except for its class. If a class method is called for a derived class, the derived class object is passed as the implied first argument.

Class methods are different than C++ or Java static methods. If you want those, see staticmethod in this section. For more information on class methods, see types.

::: {.versionchanged} 3.9 Class methods can now wrap other descriptors <descriptor> such as property. ::: :::

::: {.function} compile(source, filename, mode, flags=0, dont_inherit=False, optimize=-1)

Compile the source into a code or AST object. Code objects can be executed by exec or eval. source can either be a normal string, a byte string, or an AST object. Refer to the ast module documentation for information on how to work with AST objects.

The filename argument should give the file from which the code was read; pass some recognizable value if it wasn\'t read from a file ('<string>' is commonly used).

The mode argument specifies what kind of code must be compiled; it can be 'exec' if source consists of a sequence of statements, 'eval' if it consists of a single expression, or 'single' if it consists of a single interactive statement (in the latter case, expression statements that evaluate to something other than None will be printed).

The optional arguments flags and dont_inherit control which compiler options <ast-compiler-flags> should be activated and which future features <future> should be allowed. If neither is present (or both are zero) the code is compiled with the same flags that affect the code that is calling compile. If the flags argument is given and dont_inherit is not (or is zero) then the compiler options and the future statements specified by the flags argument are used in addition to those that would be used anyway. If dont_inherit is a non-zero integer then the flags argument is it -- the flags (future features and compiler options) in the surrounding code are ignored.

Compiler options and future statements are specified by bits which can be bitwise ORed together to specify multiple options. The bitfield required to specify a given future feature can be found as the ~__future__._Feature.compiler_flag attribute on the ~__future__._Feature instance in the __future__ module. Compiler flags <ast-compiler-flags> can be found in ast module, with PyCF_ prefix.

The argument optimize specifies the optimization level of the compiler; the default value of -1 selects the optimization level of the interpreter as given by -O options. Explicit levels are 0 (no optimization; __debug__ is true), 1 (asserts are removed, __debug__ is false) or 2 (docstrings are removed too).

This function raises SyntaxError if the compiled source is invalid, and ValueError{.interpreted-text role="exc"} if the source contains null bytes.

If you want to parse Python code into its AST representation, see ast.parse.

::: {.audit-event} compile source,filename compile

Raises an auditing event <auditing> compile with arguments source and filename. This event may also be raised by implicit compilation. :::

::: {.note} ::: {.admonition-title} Note :::

When compiling a string with multi-line code in 'single' or 'eval' mode, input must be terminated by at least one newline character. This is to facilitate detection of incomplete and complete statements in the code module. :::

::: {.warning} ::: {.admonition-title} Warning :::

It is possible to crash the Python interpreter with a sufficiently large/complex string when compiling to an AST object due to stack depth limitations in Python\'s AST compiler. :::

::: {.versionchanged} 3.2 Allowed use of Windows and Mac newlines. Also input in 'exec' mode does not have to end in a newline anymore. Added the optimize parameter. :::

::: {.versionchanged} 3.5 Previously, TypeError was raised when null bytes were encountered in source. :::

::: {.versionadded} 3.8 ast.PyCF_ALLOW_TOP_LEVEL_AWAIT can now be passed in flags to enable support for top-level await, async for, and async with. ::: :::

::: {.complex([real[, .imag]])} Return a complex number with the value real + imag*1j or convert a string or number to a complex number. If the first parameter is a string, it will be interpreted as a complex number and the function must be called without a second parameter. The second parameter can never be a string. Each argument may be any numeric type (including complex). If imag is omitted, it defaults to zero and the constructor serves as a numeric conversion like int and float. If both arguments are omitted, returns 0j.

For a general Python object x, complex(x) delegates to x.__complex__(). If __complex__() is not defined then it falls back to __float__. If __float__() is not defined then it falls back to __index__{.interpreted-text role="meth"}.

::: {.note} ::: {.admonition-title} Note :::

When converting from a string, the string must not contain whitespace around the central + or - operator. For example, complex('1+2j') is fine, but complex('1 + 2j') raises ValueError{.interpreted-text role="exc"}. :::

The complex type is described in typesnumeric{.interpreted-text role="ref"}.

::: {.versionchanged} 3.6 Grouping digits with underscores as in code literals is allowed. :::

::: {.versionchanged} 3.8 Falls back to __index__ if __complex__ and __float__ are not defined. ::: :::

::: {.function} delattr(object, name)

This is a relative of setattr. The arguments are an object and a string. The string must be the name of one of the object\'s attributes. The function deletes the named attribute, provided the object allows it. For example, delattr(x, 'foobar') is equivalent to del x.foobar.

Create a new dictionary. The dict object is the dictionary class. See dict{.interpreted-text role="class"} and typesmapping for documentation about this class.

For other containers see the built-in list{.interpreted-text role="class"}, set, and tuple classes, as well as the collections module. :::

::: {.function} dir([object])

Without arguments, return the list of names in the current local scope. With an argument, attempt to return a list of valid attributes for that object.

If the object has a method named __dir__{.interpreted-text role="meth"}, this method will be called and must return the list of attributes. This allows objects that implement a custom __getattr__ or __getattribute__ function to customize the way dir reports their attributes.

If the object does not provide __dir__, the function tries its best to gather information from the object\'s ~object.__dict__ attribute, if defined, and from its type object. The resulting list is not necessarily complete, and may be inaccurate when the object has a custom __getattr__.

The default dir mechanism behaves differently with different types of objects, as it attempts to produce the most relevant, rather than complete, information:

If the object is a module object, the list contains the names of the module\'s attributes.
If the object is a type or class object, the list contains the names of its attributes, and recursively of the attributes of its bases.
Otherwise, the list contains the object\'s attributes\' names, the names of its class\'s attributes, and recursively of the attributes of its class\'s base classes.

The resulting list is sorted alphabetically. For example:

>>> import struct >>> dir() # show the names in the module namespace # doctest: +SKIP [\'__builtins__\', \'__name__\', \'struct\'] >>> dir(struct) # show the names in the struct module # doctest: +SKIP [\'Struct\', \'__all__\', \'__builtins__\', \'__cached__\', \'__doc__\', \'__file__\', \'__initializing__\', \'__loader__\', \'__name__\', \'__package__\', \'_clearcache\', \'calcsize\', \'error\', \'pack\', \'pack_into\', \'unpack\', \'unpack_from\'] >>> class Shape: ... def __dir__(self): ... return [\'area\', \'perimeter\', \'location\'] >>> s = Shape() >>> dir(s) [\'area\', \'location\', \'perimeter\']

::: {.note} ::: {.admonition-title} Note :::

Because dir is supplied primarily as a convenience for use at an interactive prompt, it tries to supply an interesting set of names more than it tries to supply a rigorously or consistently defined set of names, and its detailed behavior may change across releases. For example, metaclass attributes are not in the result list when the argument is a class. ::: :::

::: {.function} divmod(a, b)

Take two (non complex) numbers as arguments and return a pair of numbers consisting of their quotient and remainder when using integer division. With mixed operand types, the rules for binary arithmetic operators apply. For integers, the result is the same as (a // b, a % b). For floating point numbers the result is (q, a % b), where q is usually math.floor(a / b) but may be 1 less than that. In any case q * b + a % b is very close to a, if a % b is non-zero it has the same sign as b, and 0 <= abs(a % b) < abs(b). :::

::: {.function} enumerate(iterable, start=0)

Return an enumerate object. iterable must be a sequence, an iterator, or some other object which supports iteration. The ~iterator.__next__{.interpreted-text role="meth"} method of the iterator returned by enumerate returns a tuple containing a count (from start which defaults to 0) and the values obtained from iterating over iterable.

>>> seasons = [\'Spring\', \'Summer\', \'Fall\', \'Winter\'] >>> list(enumerate(seasons)) [(0, \'Spring\'), (1, \'Summer\'), (2, \'Fall\'), (3, \'Winter\')] >>> list(enumerate(seasons, start=1)) [(1, \'Spring\'), (2, \'Summer\'), (3, \'Fall\'), (4, \'Winter\')]

Equivalent to:

def enumerate(sequence, start=0):
    n = start
    for elem in sequence:
        yield n, elem
        n += 1

:::

::: {.function} eval(expression[, globals[, locals]])

The arguments are a string and optional globals and locals. If provided, globals must be a dictionary. If provided, locals can be any mapping object.

The expression argument is parsed and evaluated as a Python expression (technically speaking, a condition list) using the globals and locals dictionaries as global and local namespace. If the globals dictionary is present and does not contain a value for the key __builtins__, a reference to the dictionary of the built-in module builtins is inserted under that key before expression is parsed. This means that expression normally has full access to the standard builtins module and restricted environments are propagated. If the locals dictionary is omitted it defaults to the globals dictionary. If both dictionaries are omitted, the expression is executed with the globals and locals in the environment where eval{.interpreted-text role="func"} is called. Note, eval() does not have access to the nested scopes <nested scope> (non-locals) in the enclosing environment.

The return value is the result of the evaluated expression. Syntax errors are reported as exceptions. Example:

>>> x = 1 >>> eval(\'x+1\') 2

This function can also be used to execute arbitrary code objects (such as those created by compile). In this case pass a code object instead of a string. If the code object has been compiled with 'exec' as the mode argument, eval{.interpreted-text role="func"}\'s return value will be None.

Hints: dynamic execution of statements is supported by the exec function. The globals and locals{.interpreted-text role="func"} functions returns the current global and local dictionary, respectively, which may be useful to pass around for use by eval or exec{.interpreted-text role="func"}.

If the given source is a string, then leading and trailing spaces and tabs are stripped.

See ast.literal_eval for a function that can safely evaluate strings with expressions containing only literals.

::: {.audit-event} exec code_object eval

Raises an auditing event <auditing> exec with the code object as the argument. Code compilation events may also be raised. ::: :::

::: {.index} builtin: exec :::

::: {.function} exec(object[, globals[, locals]])

This function supports dynamic execution of Python code. object must be either a string or a code object. If it is a string, the string is parsed as a suite of Python statements which is then executed (unless a syntax error occurs).¹ If it is a code object, it is simply executed. In all cases, the code that\'s executed is expected to be valid as file input (see the section \"File input\" in the Reference Manual). Be aware that the return and yield statements may not be used outside of function definitions even within the context of code passed to the exec function. The return value is None.

In all cases, if the optional parts are omitted, the code is executed in the current scope. If only globals is provided, it must be a dictionary (and not a subclass of dictionary), which will be used for both the global and the local variables. If globals and locals are given, they are used for the global and local variables, respectively. If provided, locals can be any mapping object. Remember that at module level, globals and locals are the same dictionary. If exec gets two separate objects as globals and locals, the code will be executed as if it were embedded in a class definition.

If the globals dictionary does not contain a value for the key __builtins__, a reference to the dictionary of the built-in module builtins is inserted under that key. That way you can control what builtins are available to the executed code by inserting your own __builtins__ dictionary into globals before passing it to exec.

::: {.audit-event} exec code_object exec

Raises an auditing event <auditing> exec with the code object as the argument. Code compilation events may also be raised. :::

::: {.note} ::: {.admonition-title} Note :::

The built-in functions globals and locals return the current global and local dictionary, respectively, which may be useful to pass around for use as the second and third argument to exec{.interpreted-text role="func"}. :::

::: {.note} ::: {.admonition-title} Note :::

The default locals act as described for function locals below: modifications to the default locals dictionary should not be attempted. Pass an explicit locals dictionary if you need to see effects of the code on locals after function exec returns. ::: :::

::: {.function} filter(function, iterable)

Construct an iterator from those elements of iterable for which function returns true. iterable may be either a sequence, a container which supports iteration, or an iterator. If function is None, the identity function is assumed, that is, all elements of iterable that are false are removed.

Note that filter(function, iterable) is equivalent to the generator expression (item for item in iterable if function(item)) if function is not None and (item for item in iterable if item) if function is None.

See itertools.filterfalse for the complementary function that returns elements of iterable for which function returns false. :::

::: {.float([x])} ::: {.index} single: NaN single: Infinity :::

Return a floating point number constructed from a number or string x.

If the argument is a string, it should contain a decimal number, optionally preceded by a sign, and optionally embedded in whitespace. The optional sign may be '+' or '-'; a '+' sign has no effect on the value produced. The argument may also be a string representing a NaN (not-a-number), or a positive or negative infinity. More precisely, the input must conform to the following grammar after leading and trailing whitespace characters are removed:

::: {.productionlist} float sign: \"+\" | \"-\" infinity: \"Infinity\" | \"inf\" nan: \"nan\" numeric_value: [floatnumber]{.title-ref} | [infinity]{.title-ref} | [nan]{.title-ref} numeric_string: [[sign]{.title-ref}] [numeric_value]{.title-ref} :::

Here floatnumber is the form of a Python floating-point literal, described in floating. Case is not significant, so, for example, \"inf\", \"Inf\", \"INFINITY\" and \"iNfINity\" are all acceptable spellings for positive infinity.

Otherwise, if the argument is an integer or a floating point number, a floating point number with the same value (within Python\'s floating point precision) is returned. If the argument is outside the range of a Python float, an OverflowError will be raised.

For a general Python object x, float(x) delegates to x.__float__(). If __float__() is not defined then it falls back to __index__.

If no argument is given, 0.0 is returned.

Examples:

>>> float('+1.23')
1.23
>>> float('   -12345\n')
-12345.0
>>> float('1e-003')
0.001
>>> float('+1E6')
1000000.0
>>> float('-Infinity')
-inf

The float type is described in typesnumeric{.interpreted-text role="ref"}.

::: {.versionchanged} 3.6 Grouping digits with underscores as in code literals is allowed. :::

::: {.versionchanged} 3.7 x is now a positional-only parameter. :::

::: {.versionchanged} 3.8 Falls back to __index__ if __float__ is not defined. ::: :::

::: {.index} single: __format__ single: string; format() (built-in function) :::

::: {.function} format(value[, format_spec])

Convert a value to a \"formatted\" representation, as controlled by format_spec. The interpretation of format_spec will depend on the type of the value argument, however there is a standard formatting syntax that is used by most built-in types: formatspec.

The default format_spec is an empty string which usually gives the same effect as calling str(value) <str>{.interpreted-text role="func"}.

A call to format(value, format_spec) is translated to type(value).__format__(value, format_spec) which bypasses the instance dictionary when searching for the value\'s __format__ method. A TypeError exception is raised if the method search reaches object and the format_spec is non-empty, or if either the format_spec or the return value are not strings.

::: {.versionchanged} 3.4 object().__format__(format_spec) raises TypeError if format_spec is not an empty string. :::

Return a new frozenset object, optionally with elements taken from iterable. frozenset is a built-in class. See frozenset and types-set for documentation about this class.

For other containers see the built-in set{.interpreted-text role="class"}, list, tuple, and dict{.interpreted-text role="class"} classes, as well as the collections{.interpreted-text role="mod"} module. :::

::: {.function} getattr(object, name[, default])

Return the value of the named attribute of object. name must be a string. If the string is the name of one of the object\'s attributes, the result is the value of that attribute. For example, getattr(x, 'foobar') is equivalent to x.foobar. If the named attribute does not exist, default is returned if provided, otherwise AttributeError is raised. :::

::: {.function} globals()

Return a dictionary representing the current global symbol table. This is always the dictionary of the current module (inside a function or method, this is the module where it is defined, not the module from which it is called). :::

::: {.function} hasattr(object, name)

The arguments are an object and a string. The result is True if the string is the name of one of the object\'s attributes, False if not. (This is implemented by calling getattr(object, name) and seeing whether it raises an AttributeError or not.) :::

::: {.function} hash(object)

Return the hash value of the object (if it has one). Hash values are integers. They are used to quickly compare dictionary keys during a dictionary lookup. Numeric values that compare equal have the same hash value (even if they are of different types, as is the case for 1 and 1.0).

::: {.note} ::: {.admonition-title} Note :::

For objects with custom __hash__ methods, note that hash truncates the return value based on the bit width of the host machine. See __hash__ for details. ::: :::

::: {.function} help([object])

Invoke the built-in help system. (This function is intended for interactive use.) If no argument is given, the interactive help system starts on the interpreter console. If the argument is a string, then the string is looked up as the name of a module, function, class, method, keyword, or documentation topic, and a help page is printed on the console. If the argument is any other kind of object, a help page on the object is generated.

Note that if a slash(/) appears in the parameter list of a function, when invoking help, it means that the parameters prior to the slash are positional-only. For more info, see the FAQ entry on positional-only parameters <faq-positional-only-arguments>{.interpreted-text role="ref"}.

This function is added to the built-in namespace by the site module.

::: {.versionchanged} 3.4 Changes to pydoc and inspect mean that the reported signatures for callables are now more comprehensive and consistent. ::: :::

::: {.function} hex(x)

Convert an integer number to a lowercase hexadecimal string prefixed with \"0x\". If x is not a Python int{.interpreted-text role="class"} object, it has to define an __index__{.interpreted-text role="meth"} method that returns an integer. Some examples:

>>> hex(255) \'0xff\' >>> hex(-42) \'-0x2a\'

If you want to convert an integer number to an uppercase or lower hexadecimal string with prefix or not, you can use either of the following ways:

>>> \'%#x\' % 255, \'%x\' % 255, \'%X\' % 255 (\'0xff\', \'ff\', \'FF\') >>> format(255, \'#x\'), format(255, \'x\'), format(255, \'X\') (\'0xff\', \'ff\', \'FF\') >>> f\'{255:#x}\', f\'{255:x}\', f\'{255:X}\' (\'0xff\', \'ff\', \'FF\')

See also format for more information.

::: {.index} single: file object; open() built-in function ::: :::

::: {.function} open(file, mode=\'r\', buffering=-1, encoding=None, errors=None, newline=None, closefd=True, opener=None)

Open file and return a corresponding file object{.interpreted-text role="term"}. If the file cannot be opened, an OSError is raised. See tut-files for more examples of how to use this function.

file is a path-like object giving the pathname (absolute or relative to the current working directory) of the file to be opened or an integer file descriptor of the file to be wrapped. (If a file descriptor is given, it is closed when the returned I/O object is closed, unless closefd is set to False.)

mode is an optional string that specifies the mode in which the file is opened. It defaults to 'r' which means open for reading in text mode. Other common values are 'w' for writing (truncating the file if it already exists), 'x' for exclusive creation and 'a' for appending (which on some Unix systems, means that all writes append to the end of the file regardless of the current seek position). In text mode, if encoding is not specified the encoding used is platform dependent: locale.getpreferredencoding(False) is called to get the current locale encoding. (For reading and writing raw bytes use binary mode and leave encoding unspecified.) The available modes are:

::: {#filemodes} ::: {.index} pair: file; modes ::: :::

Character Meaning

'r' open for reading (default) 'w' open for writing, truncating the file first 'x' open for exclusive creation, failing if the file already exists 'a' open for writing, appending to the end of the file if it exists 'b' binary mode 't' text mode (default) '+' open for updating (reading and writing)

The default mode is 'r' (open for reading text, synonym of 'rt'). Modes 'w+' and 'w+b' open and truncate the file. Modes 'r+' and 'r+b' open the file with no truncation.

As mentioned in the io-overview, Python distinguishes between binary and text I/O. Files opened in binary mode (including 'b' in the mode argument) return contents as bytes objects without any decoding. In text mode (the default, or when 't' is included in the mode argument), the contents of the file are returned as str, the bytes having been first decoded using a platform-dependent encoding or using the specified encoding if given.

There is an additional mode character permitted, 'U', which no longer has any effect, and is considered deprecated. It previously enabled universal newlines in text mode, which became the default behaviour in Python 3.0. Refer to the documentation of the newline <open-newline-parameter> parameter for further details.

::: {.note} ::: {.admonition-title} Note :::

Python doesn\'t depend on the underlying operating system\'s notion of text files; all the processing is done by Python itself, and is therefore platform-independent. :::

buffering is an optional integer used to set the buffering policy. Pass 0 to switch buffering off (only allowed in binary mode), 1 to select line buffering (only usable in text mode), and an integer > 1 to indicate the size in bytes of a fixed-size chunk buffer. When no buffering argument is given, the default buffering policy works as follows:

Binary files are buffered in fixed-size chunks; the size of the buffer is chosen using a heuristic trying to determine the underlying device\'s \"block size\" and falling back on io.DEFAULT_BUFFER_SIZE. On many systems, the buffer will typically be 4096 or 8192 bytes long.
\"Interactive\" text files (files for which ~io.IOBase.isatty returns True) use line buffering. Other text files use the policy described above for binary files.

encoding is the name of the encoding used to decode or encode the file. This should only be used in text mode. The default encoding is platform dependent (whatever locale.getpreferredencoding returns), but any text encoding supported by Python can be used. See the codecs module for the list of supported encodings.

errors is an optional string that specifies how encoding and decoding errors are to be handled---this cannot be used in binary mode. A variety of standard error handlers are available (listed under error-handlers), though any error handling name that has been registered with codecs.register_error is also valid. The standard names include:

'strict' to raise a ValueError exception if there is an encoding error. The default value of None has the same effect.
'ignore' ignores errors. Note that ignoring encoding errors can lead to data loss.
'replace' causes a replacement marker (such as '?') to be inserted where there is malformed data.
'surrogateescape' will represent any incorrect bytes as code points in the Unicode Private Use Area ranging from U+DC80 to U+DCFF. These private code points will then be turned back into the same bytes when the surrogateescape error handler is used when writing data. This is useful for processing files in an unknown encoding.
'xmlcharrefreplace' is only supported when writing to a file. Characters not supported by the encoding are replaced with the appropriate XML character reference &#nnn;.
'backslashreplace' replaces malformed data by Python\'s backslashed escape sequences.
'namereplace' (also only supported when writing) replaces unsupported characters with \N{...} escape sequences.

::: {.index} single: universal newlines; open() built-in function :::

::: {#open-newline-parameter} newline controls how universal newlines{.interpreted-text role="term"} mode works (it only applies to text mode). It can be None, '', '\n', '\r', and '\r\n'. It works as follows: :::

When reading input from the stream, if newline is None, universal newlines mode is enabled. Lines in the input can end in '\n', '\r', or '\r\n', and these are translated into '\n' before being returned to the caller. If it is '', universal newlines mode is enabled, but line endings are returned to the caller untranslated. If it has any of the other legal values, input lines are only terminated by the given string, and the line ending is returned to the caller untranslated.
When writing output to the stream, if newline is None, any '\n' characters written are translated to the system default line separator, os.linesep. If newline is '' or '\n', no translation takes place. If newline is any of the other legal values, any '\n' characters written are translated to the given string.

If closefd is False and a file descriptor rather than a filename was given, the underlying file descriptor will be kept open when the file is closed. If a filename is given closefd must be True (the default) otherwise an error will be raised.

A custom opener can be used by passing a callable as opener. The underlying file descriptor for the file object is then obtained by calling opener with (file, flags). opener must return an open file descriptor (passing os.open as opener results in functionality similar to passing None).

The newly created file is non-inheritable <fd_inheritance>.

The following example uses the dir_fd <dir_fd>{.interpreted-text role="ref"} parameter of the os.open function to open a file relative to a given directory:

>>> import os
>>> dir_fd = os.open('somedir', os.O_RDONLY)
>>> def opener(path, flags):
...     return os.open(path, flags, dir_fd=dir_fd)
...
>>> with open('spamspam.txt', 'w', opener=opener) as f:
...     print('This will be written to somedir/spamspam.txt', file=f)
...
>>> os.close(dir_fd)  # don't leak a file descriptor

The type of file object returned by the open function depends on the mode. When open is used to open a file in a text mode ('w', 'r', 'wt', 'rt', etc.), it returns a subclass of io.TextIOBase (specifically io.TextIOWrapper). When used to open a file in a binary mode with buffering, the returned class is a subclass of io.BufferedIOBase. The exact class varies: in read binary mode, it returns an io.BufferedReader; in write binary and append binary modes, it returns an io.BufferedWriter{.interpreted-text role="class"}, and in read/write mode, it returns an io.BufferedRandom. When buffering is disabled, the raw stream, a subclass of io.RawIOBase{.interpreted-text role="class"}, io.FileIO, is returned.

::: {.index} single: line-buffered I/O single: unbuffered I/O single: buffer size, I/O single: I/O control; buffering single: binary mode single: text mode module: sys :::

See also the file handling modules, such as, fileinput, io{.interpreted-text role="mod"} (where open is declared), os, os.path{.interpreted-text role="mod"}, tempfile, and shutil.

::: {.audit-event} open file,mode,flags open :::

The mode and flags arguments may have been modified or inferred from the original call.

::: {.versionchanged} 3.3

The opener parameter was added.
The 'x' mode was added.
IOError used to be raised, it is now an alias of OSError.
FileExistsError is now raised if the file opened in exclusive creation mode ('x') already exists. :::

::: {.versionchanged} 3.4

The file is now non-inheritable. :::

::: {.deprecated-removed} 3.4 3.10

The 'U' mode. :::

::: {.versionchanged} 3.5

If the system call is interrupted and the signal handler does not raise an exception, the function now retries the system call instead of raising an InterruptedError exception (see 475 for the rationale).
The 'namereplace' error handler was added. :::

::: {.versionchanged} 3.6

Support added to accept objects implementing os.PathLike.
On Windows, opening a console buffer may return a subclass of io.RawIOBase other than io.FileIO. ::: :::

::: {.function} ord(c)

Given a string representing one Unicode character, return an integer representing the Unicode code point of that character. For example, ord('a') returns the integer 97 and ord('€') (Euro sign) returns 8364. This is the inverse of chr. :::

::: {.function} pow(base, exp[, mod])

Return base to the power exp; if mod is present, return base to the power exp, modulo mod (computed more efficiently than pow(base, exp) % mod). The two-argument form pow(base, exp) is equivalent to using the power operator: base**exp.

The arguments must have numeric types. With mixed operand types, the coercion rules for binary arithmetic operators apply. For int operands, the result has the same type as the operands (after coercion) unless the second argument is negative; in that case, all arguments are converted to float and a float result is delivered. For example, 10**2 returns 100, but 10**-2 returns 0.01.

For int operands base and exp, if mod is present, mod must also be of integer type and mod must be nonzero. If mod is present and exp is negative, base must be relatively prime to mod. In that case, pow(inv_base, -exp, mod) is returned, where inv_base is an inverse to base modulo mod.

Here\'s an example of computing an inverse for 38 modulo 97:

>>> pow(38, -1, mod=97)
23
>>> 23 * 38 % 97 == 1
True

::: {.versionchanged} 3.8 For int operands, the three-argument form of pow now allows the second argument to be negative, permitting computation of modular inverses. :::

::: {.versionchanged} 3.8 Allow keyword arguments. Formerly, only positional arguments were supported. ::: :::

::: {.function} print(*objects, sep=\' \', end=\'\n\', file=sys.stdout, flush=False)

Print objects to the text stream file, separated by sep and followed by end. sep, end, file and flush, if present, must be given as keyword arguments.

All non-keyword arguments are converted to strings like str does and written to the stream, separated by sep and followed by end. Both sep and end must be strings; they can also be None, which means to use the default values. If no objects are given, print will just write end.

The file argument must be an object with a write(string) method; if it is not present or None, sys.stdout will be used. Since printed arguments are converted to text strings, print cannot be used with binary mode file objects. For these, use file.write(...) instead.

Whether output is buffered is usually determined by file, but if the flush keyword argument is true, the stream is forcibly flushed.

::: {.versionchanged} 3.3 Added the flush keyword argument. ::: :::

::: {.property(fget=None, .fset=None, .fdel=None, .doc=None)} Return a property attribute.

fget is a function for getting an attribute value. fset is a function for setting an attribute value. fdel is a function for deleting an attribute value. And doc creates a docstring for the attribute.

A typical use is to define a managed attribute x:

class C:
    def __init__(self):
        self._x = None

    def getx(self):
        return self._x

    def setx(self, value):
        self._x = value

    def delx(self):
        del self._x

    x = property(getx, setx, delx, "I'm the 'x' property.")

If c is an instance of C, c.x will invoke the getter, c.x = value will invoke the setter and del c.x the deleter.

If given, doc will be the docstring of the property attribute. Otherwise, the property will copy fget\'s docstring (if it exists). This makes it possible to create read-only properties easily using property as a decorator:

class Parrot:
    def __init__(self):
        self._voltage = 100000

    @property
    def voltage(self):
        """Get the current voltage."""
        return self._voltage

The @property decorator turns the voltage{.interpreted-text role="meth"} method into a \"getter\" for a read-only attribute with the same name, and it sets the docstring for voltage to \"Get the current voltage.\"

A property object has ~property.getter, ~property.setter, and ~property.deleter methods usable as decorators that create a copy of the property with the corresponding accessor function set to the decorated function. This is best explained with an example:

class C:
    def __init__(self):
        self._x = None

    @property
    def x(self):
        """I'm the 'x' property."""
        return self._x

    @x.setter
    def x(self, value):
        self._x = value

    @x.deleter
    def x(self):
        del self._x

This code is exactly equivalent to the first example. Be sure to give the additional functions the same name as the original property (x in this case.)

The returned property object also has the attributes fget, fset, and fdel corresponding to the constructor arguments.

::: {.versionchanged} 3.5 The docstrings of property objects are now writeable. :::

Rather than being a function, range is actually an immutable sequence type, as documented in typesseq-range and typesseq. :::

::: {.function} repr(object)

Return a string containing a printable representation of an object. For many types, this function makes an attempt to return a string that would yield an object with the same value when passed to eval, otherwise the representation is a string enclosed in angle brackets that contains the name of the type of the object together with additional information often including the name and address of the object. A class can control what this function returns for its instances by defining a __repr__{.interpreted-text role="meth"} method. :::

::: {.function} reversed(seq)

Return a reverse iterator. seq must be an object which has a __reversed__ method or supports the sequence protocol (the __len__ method and the __getitem__ method with integer arguments starting at 0). :::

::: {.function} round(number[, ndigits])

Return number rounded to ndigits precision after the decimal point. If ndigits is omitted or is None, it returns the nearest integer to its input.

For the built-in types supporting round{.interpreted-text role="func"}, values are rounded to the closest multiple of 10 to the power minus ndigits; if two multiples are equally close, rounding is done toward the even choice (so, for example, both round(0.5) and round(-0.5) are 0, and round(1.5) is 2). Any integer value is valid for ndigits (positive, zero, or negative). The return value is an integer if ndigits is omitted or None. Otherwise the return value has the same type as number.

For a general Python object number, round delegates to number.__round__.

::: {.note} ::: {.admonition-title} Note :::

The behavior of round for floats can be surprising: for example, round(2.675, 2) gives 2.67 instead of the expected 2.68. This is not a bug: it\'s a result of the fact that most decimal fractions can\'t be represented exactly as a float. See tut-fp-issues for more information. :::

Return a new set object, optionally with elements taken from iterable. set is a built-in class. See set and types-set{.interpreted-text role="ref"} for documentation about this class.

For other containers see the built-in frozenset{.interpreted-text role="class"}, list, tuple, and dict{.interpreted-text role="class"} classes, as well as the collections{.interpreted-text role="mod"} module. :::

::: {.function} setattr(object, name, value)

This is the counterpart of getattr. The arguments are an object, a string and an arbitrary value. The string may name an existing attribute or a new attribute. The function assigns the value to the attribute, provided the object allows it. For example, setattr(x, 'foobar', 123) is equivalent to x.foobar = 123. :::

::: {.slice(stop) .slice(start, .stop[, .step])} Return a slice object representing the set of indices specified by range(start, stop, step). The start and step arguments default to None. Slice objects have read-only data attributes ~slice.start, ~slice.stop and ~slice.step which merely return the argument values (or their default). They have no other explicit functionality; however they are used by NumPy and other third party packages. Slice objects are also generated when extended indexing syntax is used. For example: a[start:stop:step] or a[start:stop, i]. See itertools.islice for an alternate version that returns an iterator. :::

::: {.function} sorted(iterable, *, key=None, reverse=False)

Return a new sorted list from the items in iterable.

Has two optional arguments which must be specified as keyword arguments.

key specifies a function of one argument that is used to extract a comparison key from each element in iterable (for example, key=str.lower). The default value is None (compare the elements directly).

reverse is a boolean value. If set to True, then the list elements are sorted as if each comparison were reversed.

Use functools.cmp_to_key to convert an old-style cmp function to a key function.

The built-in sorted function is guaranteed to be stable. A sort is stable if it guarantees not to change the relative order of elements that compare equal --- this is helpful for sorting in multiple passes (for example, sort by department, then by salary grade).

For sorting examples and a brief sorting tutorial, see sortinghowto. :::

::: {.decorator} staticmethod

Transform a method into a static method.

A static method does not receive an implicit first argument. To declare a static method, use this idiom:

class C:
    @staticmethod
    def f(arg1, arg2, ...): ...

The @staticmethod form is a function decorator{.interpreted-text role="term"} -- see function for details.

A static method can be called either on the class (such as C.f()) or on an instance (such as C().f()).

Static methods in Python are similar to those found in Java or C++. Also see classmethod for a variant that is useful for creating alternate class constructors.

Like all decorators, it is also possible to call staticmethod as a regular function and do something with its result. This is needed in some cases where you need a reference to a function from a class body and you want to avoid the automatic transformation to instance method. For these cases, use this idiom:

class C:
    builtin_open = staticmethod(open)

For more information on static methods, see types{.interpreted-text role="ref"}. :::

::: {.index} single: string; str() (built-in function)

Return a str version of object. See str for details.

str is the built-in string class. For general information about strings, see textseq{.interpreted-text role="ref"}. :::

::: {.function} sum(iterable, /, start=0)

Sums start and the items of an iterable from left to right and returns the total. The iterable\'s items are normally numbers, and the start value is not allowed to be a string.

For some use cases, there are good alternatives to sum. The preferred, fast way to concatenate a sequence of strings is by calling ''.join(sequence). To add floating point values with extended precision, see math.fsum. To concatenate a series of iterables, consider using itertools.chain{.interpreted-text role="func"}.

::: {.versionchanged} 3.8 The start parameter can be specified as a keyword argument. ::: :::

::: {.function} super([type[, object-or-type]])

Return a proxy object that delegates method calls to a parent or sibling class of type. This is useful for accessing inherited methods that have been overridden in a class.

The object-or-type determines the method resolution order to be searched. The search starts from the class right after the type.

For example, if ~class.__mro__ of object-or-type is D -> B -> C -> A -> object and the value of type is B, then super searches C -> A -> object.

The ~class.__mro__ attribute of the object-or-type lists the method resolution search order used by both getattr and super{.interpreted-text role="func"}. The attribute is dynamic and can change whenever the inheritance hierarchy is updated.

If the second argument is omitted, the super object returned is unbound. If the second argument is an object, isinstance(obj, type) must be true. If the second argument is a type, issubclass(type2, type) must be true (this is useful for classmethods).

There are two typical use cases for super. In a class hierarchy with single inheritance, super can be used to refer to parent classes without naming them explicitly, thus making the code more maintainable. This use closely parallels the use of super in other programming languages.

The second use case is to support cooperative multiple inheritance in a dynamic execution environment. This use case is unique to Python and is not found in statically compiled languages or languages that only support single inheritance. This makes it possible to implement \"diamond diagrams\" where multiple base classes implement the same method. Good design dictates that this method have the same calling signature in every case (because the order of calls is determined at runtime, because that order adapts to changes in the class hierarchy, and because that order can include sibling classes that are unknown prior to runtime).

For both use cases, a typical superclass call looks like this:

class C(B):
    def method(self, arg):
        super().method(arg)    # This does the same thing as:
                               # super(C, self).method(arg)

In addition to method lookups, super also works for attribute lookups. One possible use case for this is calling descriptors <descriptor> in a parent or sibling class.

Note that super is implemented as part of the binding process for explicit dotted attribute lookups such as super().__getitem__(name). It does so by implementing its own __getattribute__ method for searching classes in a predictable order that supports cooperative multiple inheritance. Accordingly, super is undefined for implicit lookups using statements or operators such as super()[name].

Also note that, aside from the zero argument form, super is not limited to use inside methods. The two argument form specifies the arguments exactly and makes the appropriate references. The zero argument form only works inside a class definition, as the compiler fills in the necessary details to correctly retrieve the class being defined, as well as accessing the current instance for ordinary methods.

For practical suggestions on how to design cooperative classes using super, see guide to using super().

Rather than being a function, tuple is actually an immutable sequence type, as documented in typesseq-tuple and typesseq. :::

::: {.type(object) .type(name, .bases, .dict)} ::: {.index} object: type :::

With one argument, return the type of an object. The return value is a type object and generally the same object as returned by object.__class__ <instance.__class__>.

The isinstance built-in function is recommended for testing the type of an object, because it takes subclasses into account.

With three arguments, return a new type object. This is essentially a dynamic form of the class statement. The name string is the class name and becomes the ~definition.__name__ attribute; the bases tuple itemizes the base classes and becomes the ~class.__bases__ attribute; and the dict dictionary is the namespace containing definitions for class body and is copied to a standard dictionary to become the ~object.__dict__ attribute. For example, the following two statements create identical type objects:

>>> class X: ... a = 1 ... >>> X = type(\'X\', (object,), dict(a=1))