Print Python docstrings when module is executed interactively

Question

I have written a module, which should only be used by means of import, then call the functions as required.

I do not want this module to do anything when ran interactively, other than printing out the docstrings of all the functions, which have docstrings, and which are not starting with '_'

I am looking for tips/tricks to improve this code. Is there an alternative way, as I am not very skilled in the inspect module nor in sys.modules:

import sys
import inspect

def function1():
    """
    docstring of function1

    usage:

    import thismodule
    a = thismodule.function1()
    """
    pass

def function2():
    """
    docstring of function2

    usage:

    import thismodule
    a = thismodule.function2()
    """
    pass

def function3():
    #this function has not docstring
    #therefor should not be printed
    pass

def _function4():
    """
    this function has a docstring
    but the name starts with _ indicating an internal funciton

    this should not be printed
    """
    pass

def main():
    for name, obj in inspect.getmembers(sys.modules[__name__]):
        if (
            (inspect.isfunction(obj))         ## only functions
            and (obj.__module__ == __name__)  ## only for this module
            and (name[0:1] != '_')            ## no internals
            and (obj.__doc__ != None)         ## __doc__ must be defined
            ):
            print('****************************')
            print('function: ' + name + '()')
            print(obj.__doc__)
    print('****************************')


if __name__ == '__main__':
    main()