Editing Python (programming language) (section)

===Typing===
[[File:Python 3.13 Standrd Type Hierarchy-en.svg|thumb|The standard type hierarchy in Python&nbsp;3]]
Python uses [[duck typing]], and it has typed objects but untyped variable names. Type constraints are not checked at definition time; rather, operations on an object may fail at usage time, indicating that the object is not of an appropriate type. Despite being [[dynamically typed]], Python is [[strongly typed]], forbidding operations that are poorly defined (e.g., adding a number and a string) rather than quietly attempting to interpret them.

Python allows programmers to define their own types using [[class (computer science)|classes]], most often for [[object-oriented programming]]. New [[object (computer science)|instances]] of classes are constructed by calling the class, for example, {{code|lang=python|code=SpamClass()}} or {{code|lang=python|code=EggsClass()}}); the classes are instances of the [[metaclass]] <code>type</code> (which is an instance of itself), thereby allowing metaprogramming and [[Reflective programming|reflection]].

Before version 3.0, Python had two kinds of classes, both using the same syntax: ''old-style'' and ''new-style''.<ref name="classy"/> Current Python versions support the semantics of only the new style.

Python supports [[optional typing|optional type annotations]].<ref name="type_hint-PEP"/><ref>{{Cite web |title=PEP 484 – Type Hints {{!}} peps.python.org |url=https://peps.python.org/pep-0484/ |access-date=2023-11-29 |website=peps.python.org |archive-date=27 November 2023 |archive-url=https://web.archive.org/web/20231127205023/https://peps.python.org/pep-0484/ |url-status=live}}</ref> These annotations are not enforced by the language, but may be used by external tools such as '''mypy''' to catch errors.<ref>{{cite web |title=typing — Support for type hints |url=https://docs.python.org/3/library/typing.html |website=Python documentation |publisher=Python Software Foundation |access-date=22 December 2023 |archive-date=21 February 2020 |archive-url=https://web.archive.org/web/20200221184042/https://docs.python.org/3/library/typing.html |url-status=live}}</ref><ref>{{cite web |url=http://mypy-lang.org/ |title=mypy – Optional Static Typing for Python |access-date=28 January 2017 |archive-date=6 June 2020 |archive-url=https://web.archive.org/web/20200606192012/http://mypy-lang.org/ |url-status=live}}</ref> Mypy also supports a Python compiler called mypyc, which leverages type annotations for optimization.<ref>{{cite web |title=Introduction |url=https://mypyc.readthedocs.io/en/latest/introduction.html |website=mypyc.readthedocs.io |access-date=22 December 2023 |archive-date=22 December 2023 |archive-url=https://web.archive.org/web/20231222000457/https://mypyc.readthedocs.io/en/latest/introduction.html |url-status=live}}</ref>

{|class="wikitable"
|+ Summary of Python 3's built-in types
|-
! Type
! [[immutable object|Mutability]]
! Description
! Syntax examples
|-
| <code>bool</code>
| immutable
| [[Boolean value]]
| {{code|lang=python|True}}<br />{{code|lang=python|False}}
|-
| <code>bytearray</code>
| mutable
| Sequence of [[byte]]s
| {{code|lang=python|bytearray(b'Some ASCII')}}<br />{{code|lang=python|bytearray(b"Some ASCII")}}<br />{{code|lang=python|bytearray([119, 105, 107, 105])}}
|-
| <code>bytes</code>
| immutable
| Sequence of bytes
| {{code|lang=python|b'Some ASCII'}}<br />{{code|lang=python|b"Some ASCII"}}<br />{{code|lang=python|bytes([119, 105, 107, 105])}}
|-
| <code>complex</code>
| immutable
| [[Complex number]] with real and imaginary parts
| {{code|lang=python|3+2.7j}}<br />{{code|lang=python|3 + 2.7j}}
|-
| <code>dict</code>
| mutable
| [[Associative array]] (or dictionary) of key and value pairs; can contain mixed types (keys and values); keys must be a hashable type
| {{code|lang=python|{'key1': 1.0, 3: False} }}<br />{{code|lang=python| {} }}
|-
| <code>types.EllipsisType</code>
| immutable
| An [[Ellipsis (programming operator)|ellipsis]] placeholder to be used as an index in [[NumPy]] arrays
| {{code|lang=python|...}}<br />{{code|lang=python|Ellipsis}}
|-
| <code>float</code>
| immutable
| [[Double-precision]] [[floating-point number]]. The precision is machine-dependent, but in practice it is generally implemented as a 64-bit [[IEEE&nbsp;754]] number with 53&nbsp;bits of precision.<ref>{{Cite web
 |title=15. Floating Point Arithmetic: Issues and Limitations – Python 3.8.3 documentation
 |url=https://docs.python.org/3.8/tutorial/floatingpoint.html#representation-error
 |access-date=6 June 2020
 |website=docs.python.org
 |quote=Almost all machines today (November 2000) use IEEE-754 floating point arithmetic, and almost all platforms map Python floats to IEEE-754 "double precision".
 |archive-date=6 June 2020
 |archive-url=https://web.archive.org/web/20200606113842/https://docs.python.org/3.8/tutorial/floatingpoint.html#representation-error
 |url-status=live
}}</ref>
|
{{code|lang=python|1.33333}}
|-
| <code>frozenset</code>
| immutable
| Unordered [[set (computer science)|set]], contains no duplicates; can contain mixed types, if hashable
| {{nobr|{{code|lang=python|frozenset([4.0, 'string', True])}}}}
|-
| <code>int</code>
| immutable
| [[Integer (computer science)|Integer]] of unlimited magnitude<ref name="pep0237"/>
| {{code|lang=python|42}}
|-
| <code>list</code>
| mutable
| [[list (computer science)|List]], can contain mixed types
| {{code|lang=python|[4.0, 'string', True]}}<br />{{code|lang=python|[]}}
|-
| <code>types.NoneType</code>
| immutable
| An object representing the absence of a value, often called [[null pointer|null]] in other languages
| {{code|lang=python|None}}
|-
| <code>types.NotImplementedType</code>
| immutable
| A placeholder that can be returned from [[Operator overloading|overloaded operators]] to indicate unsupported operand types.
| {{code|lang=python|NotImplemented}}
|-
| <code>range</code>
| immutable
| An ''immutable sequence'' of numbers, commonly used for iterating a specific number of times in <code>for</code> loops<ref>{{cite web |title=Built-in Types |url=https://docs.python.org/3/library/stdtypes.html#typesseq-range |access-date=3 October 2019 |archive-date=14 June 2020 |archive-url=https://web.archive.org/web/20200614194325/https://docs.python.org/3/library/stdtypes.html#typesseq-range |url-status=live}}</ref>
| {{code|lang=python|range(−1, 10)}}<br />{{code|lang=python|range(10, −5, −2)}}
|-
| <code>set</code>
| mutable
| Unordered [[set (computer science)|set]], contains no duplicates; can contain mixed types, if hashable
| {{code|lang=python| {4.0, 'string', True} }}<br />{{code|lang=python|set()}}
|-
| <code>str</code>
| immutable
| A [[character string]]: sequence of Unicode codepoints
| {{code|lang=python|'Wikipedia'}}<br />{{code|lang=python|"Wikipedia"}}<syntaxhighlight lang="python">"""Spanning
multiple
lines"""</syntaxhighlight><syntaxhighlight lang="python">
Spanning
multiple
lines
</syntaxhighlight>
|-
| <code>tuple</code>
| immutable
| [[Tuple]], can contain mixed types
| {{code|lang=python|(4.0, 'string', True)}}<br />{{code|lang=python|('single element',)}}<br />{{code|lang=python|()}}
|}