Experimental type system extensions for mypy typechecker (Python 3)

 Add type annotations to your Python programs, and use mypy to type check them.
 Mypy is essentially a Python linter on steroids, and it can catch many
 programming errors by analyzing your program, without actually having to run
 it. Mypy has a powerful type system with features such as type inference,
 gradual typing, generics and union types.
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 The "mypy_extensions" module defines experimental extensions to the
 standard "typing" module that are supported by the mypy typechecker.
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 This package provides the modules for Python 3.