pep 362 example

gistfile1.py

def render_signature(signature):
    '''Renders function definition by its signature.

    Example:

        >>> def test(a:'foo', *, b:'bar', c=True, **kwargs:None) -> 'spam':
        ...    pass

        >>> render_signature(inspect.signature(test))
        test(a:'foo', *, b:'bar', c=True, **kwargs:None) -> 'spam'
    '''

    def render_param(param):
        '''A helper to render a single parameter, with its default
        value and annotation'''

        result = param.name

        # Add annotation and default value
        if hasattr(param, 'annotation'):
            result = '{}:{!r}'.format(result, param.annotation)
        if hasattr(param, 'default'):
            result = '{}={!r}'.format(result, param.default)

        # Handle *args & **kwargs -like parameters
        if param.is_args:
            result = '*' + result
        elif param.is_kwargs:
            result = '**' + result

        return result

    result = []
    render_kw_only_separator = True
    for param in signature.parameters.values():
        rendered = render_param(param)
        if param.is_args:
            # OK, we have an '*args'-like parameter, so we won't need
            # a '*' to separate keyword-only arguments
            render_kw_only_separator = False
        elif param.is_keyword_only and render_kw_only_separator:
            # We have a keyword-only parameter to render and we haven't 
            # rendered an '*args'-like parameter before, so add a '*'
            # separator to the parameters list ("foo(arg1, *, arg2)" case)
            result.append('*')
            # This condition should be only triggered once, so
            # reset the flag
            render_kw_only_separator = False
        result.append(rendered)

    result = '{}({})'.format(signature.name, ', '.join(result))

    if hasattr(signature, 'return_annotation'):
        result += ' -> {!r}'.format(signature.return_annotation)

    return result