Type of the containing class for instance methods, and a type object If it is not annotated, then it is assumed to have the An exception is the first argument of instance andĬlass methods. For a checkedįunction, the default annotation for arguments and for the return type It is recommended but not required that checked functions haveĪnnotations for all arguments and the return type. With the decorator should be treated as having General type possible, or ignored, by any type checker. The meaning of annotationsĪny function without annotations should be treated as having the most Typed language, and the authors have no desire to ever make type hints It should also be emphasized that Python will remain a dynamically Optimizations is left as an exercise for the reader. Implement specific runtime type checking functionality, for example Runtime type checking – in particular the get_type_hints()įunction – third party packages would have to be developed to While the proposed typing module will contain some building blocks for Support for off-line type checkers such as mypy, as well as providingĪ standard notation that can be used by IDEs for code completion and Of these goals, static analysis is the most important. Potential runtime type checking, and (perhaps, in some contexts)Ĭode generation utilizing type information. Opening up Python code to easier static analysis and refactoring, This PEP aims to provide a standard syntax for type annotations, Hinting, which is listed as the first possible use case Then, there has always been an implicit goal to use them for type Although no meaning was assigned to annotations PEP 3107 added support for arbitrary annotations on parts of aįunction definition. Other approaches from which we have borrowed or to which ours can beĬompared and contrasted are described in PEP 482. Gradual typing and the full type system are explained in PEP 483. This latter feature is taken from the idea of gradual typing. The type system supports unions, generic types, and a special type (but its significance is primarily to an offline type checker). Works at runtime by implementing _getitem_() in the metaclass The example here uses a custom type Sequence, importedįrom a pure-Python module typing. Square brackets mean that no new syntax needs to be added to the Type “sequence of integers” can be written as Sequence. The proposal is strongly inspired by mypy. JIT optimization, those tools are not yet as mature.) (While it would of course be possible for individual users to employĪ similar checker at run time for Design By Contract enforcement or Type checker which users can run over their source code voluntarily.Įssentially, such a type checker acts as a very powerful linter. Instead, the proposal assumes the existence of a separate off-line _annotations_ attribute, no type checking happens at runtime. While these annotations are available at runtime through the usual Simply enables better coordination, as PEP 333 did for web frameworks.įor example, here is a simple function whose argument and return typeĭef greeting ( name : str ) -> str : return 'Hello ' + name Of annotations, even when they conform to this specification. Note that this PEP still explicitly does NOT prevent other uses ofĪnnotations, nor does it require (or forbid) any particular processing This PEP introduces a provisional module to provide these standardĭefinitions and tools, along with some conventions for situations Usage for static type analysis that the community would benefit fromĪ standard vocabulary and baseline tools within the standard library. PEP 3107 introduced syntax for function annotations, but the semantics What about existing uses of annotations?.Which brackets for generic type parameters?.Suggested syntax for Python 2.7 and straddling code.Compatibility with other uses of function annotations.Annotating generator functions and coroutines.Arbitrary argument lists and default argument values. Arbitrary generic types as base classes.Instantiating generic classes and type erasure.Toggle light / dark / auto colour theme PEP 484 – Type Hints Author : Guido van Rossum, Jukka Lehtosalo, Łukasz Langa BDFL-Delegate : Mark Shannon Discussions-To : Python-Dev list Status : Final Type : Standards Track Topic : Typing Created : 2 Python-Version : 3.5 Post-History : 1, 2, 1, 2, 2 Resolution : Python-Dev message PEP 484 – Type Hints | Following system colour scheme Selected dark colour scheme Selected light colour scheme Python Enhancement Proposals
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