Typeguard

This library provides run-time type checking for functions defined with PEP 484 argument (and return) type annotations.

Three principal ways to do type checking are provided, each with its pros and cons:

1. the check_argument_types() and check_return_type() functions:

   • debugger friendly (except when running with the pydev debugger with the C extension installed)

   • does not work reliably with dynamically defined type hints (e.g. in nested functions)

2. the @typechecked decorator:

   • automatically type checks yields and sends of returned generators (regular and async)

   • adds an extra frame to the call stack for every call to a decorated function

3. the stack profiler hook (with TypeChecker('packagename'):) (deprecated):

   • emits warnings instead of raising TypeError

   • requires very few modifications to the code

   • multiple TypeCheckers can be stacked/nested

   • does not work reliably with dynamically defined type hints (e.g. in nested functions)

   • may cause problems with badly behaving debuggers or profilers

   • cannot distinguish between an exception being raised and a None being returned

4. the import hook (typeguard.importhook.install_import_hook()):

   • automatically annotates classes and functions with @typechecked on import

   • no code changes required in target modules

   • requires imports of modules you need to check to be deferred until after the import hook has been installed

   • may clash with other import hooks

Quick links

• User guide
• API reference
• Version history