.. blogpost:: :title: Missing signature for functions :keywords: signature, inspect :date: 2018-08-03 :categories: python The signature of a function is not always available in :epkg:`Python`. The buildin functions do not follow the same pattern as functions written in :epkg:`Python` but they provide a backup plan with the attribute ``__text_signature__``: .. runpython:: :showcode: print(open.__text_signature__) As a result, ``inspect.signature(open)`` returns a non empty result. However, for a function defined with `pybind11 `_, this backup plan is not available: `Set the __text_signature__ attribute of callables `_. That's why the class :class:`AutoSignatureDirective ` may or may not work with regular expressions parsing the documentation computed by *pybind11* as a same function could have several :epkg:`C++` signature with different types.