The typing_extensions module contains both backports of typing features as well as experimental types that will eventually be added to the typing module, such as Protocol (see PEP 544 for details about protocols and static duck typing) or TypedDict (see PEP 589).
Users of other Python versions should continue to install and use the typing module from PyPi instead of using this one unless specifically writing code that must be compatible with multiple Python versions or requires experimental types.
Starting with version 4.0.0, typing_extensions uses Semantic Versioning. The major version is incremented for all backwards-incompatible changes, including dropping support for older Python versions. Therefore, it's safe to depend on typing_extensions like this: typing_extensions >=x.y, <(x+1), where x.y is the first version that includes all features you need.
This module currently contains the following:
AnnotatedAsyncContextManagerAsyncGeneratorAsyncIterableAsyncIteratorAwaitableChainMapClassVarConcatenateContextManagerCoroutineCounterDefaultDictDequefinalFinalLiteralNewTypeNoReturnNotRequiredoverloadOrderedDictParamSpecParamSpecArgsParamSpecKwargsProtocolRequiredruntime_checkableTextTypeTypedDictTypeAliasTypeGuardTYPE_CHECKING
get_originget_argsget_type_hints
There are a few types whose interface was modified between different versions of typing. For example, typing.Sequence was modified to subclass typing.Reversible as of Python 3.5.3.
These changes are _not backported to prevent subtle compatibility issues when mixing the differing implementations of modified classes.
Certain types have incorrect runtime behavior due to limitations of older versions of the typing module. For example, ParamSpec and Concatenate will not work with get_args, get_origin. Certain PEP 612 special cases in user-defined Generics are also not available. These types are only guaranteed to work for static type checking.
To run tests, navigate into the appropriate source directory and run test_typing_extensions.py. You will also need to install the latest version of typing if you are using a version of Python that does not include typing as a part of the standard library.