Get Type Annotations In Python 3.7

Question

I would like to simply access the type annotations that I've declared in my class definition's __init__ method:

class Cls:
    def __init__(self, data: dict)
        pass

def get_type(function):
    # What goes here?

cls = Cls({})

get_type(cls.__init__) # Returns 'dict' type.

Answer 1

import inspect

def get_type(function):
    print(inspect.formatargspec(*inspect.getfullargspec(function)))

will print (self, data: dict) .

Answer 2

Use the inspect modules getmembers function: https://docs.python.org/3/library/inspect.html

It returns a list of members for whatever object you pass. If you pass a function, it will include a two-tuple where the first element is '__annotations__' and the second element is a dictionary that maps the parameter name to type annotation. Currently (Python 3.7) the getmembers function will return the '__annotations__' tuple as the first element, so the following will work:

import inspect

class Cls:
    def __init__(self, data: dict)
        pass

def get_type(function, param_name):
    return inspect.getmembers(function)[0][1][param_name]

cls = Cls({})

get_type(cls.__init__, 'data') # Returns dict