forge (python) signatures for fun and profit

Release v18.6.0 (What’s new?).

forge is an elegant Python package for revising function signatures at runtime. This libraries aim is to help you write better, more literate code with less boilerplate.


forge is a Python-only package hosted on PyPI for Python 3.5+.

The recommended installation method is pip-installing into a virtualenv:

$ pip install python-forge


  • Philosophy walks you through the design considerations and need for forge. Read this to understand the value proposition through a case-study review of the standard library’s logging module.
  • Signatures, parameters and return types gives a comprehensive overview of the forge data structures. Read this to learn how to take full advantage of the power of forge.
  • Revising signatures (i.e. forging a signature) describes the signature revision utilities included with forge. This is a narrative on how to use “the features”.
  • Patterns and usage depicts some common use-cases and approaches for using forge.
  • API Reference has documentation for all public functionality.
  • Glossary irons-out the terminology necessary to harness the power of forge.

Consider a library like requests that provides a useful API for performing HTTP requests. Every HTTP method has it’s own function which is a thin wrapper around requests.Session.request. The code is a little more than 150 lines, with about 90% of that being boilerplate. Using forge we can get that back down to about 10% it’s current size, while increasing the literacy of the code.

import forge
import requests

request = forge.copy(requests.Session.request, exclude='self')(requests.request)

def with_method(method):
    revised = forge.modify(
        'method', default=method, bound=True,
    revised.__name__ = method.lower()
    return revised

post = with_method('POST')
get = with_method('GET')
put = with_method('PUT')
delete = with_method('DELETE')
options = with_method('OPTIONS')
head = with_method('HEAD')
patch = with_method('PATCH')

So what happened? The first thing we did was create an alternate request function to replace requests.request that provides the exact same functionality but makes its parameters explicit:

# requests.get() looks like this:
assert forge.repr_callable(requests.get) == 'get(url, params=None, **kwargs)'

# our get() calls the same code, but looks like this:
assert forge.repr_callable(get) == (
    'get(url, params=None, data=None, headers=None, cookies=None, '
        'files=None, auth=None, timeout=None, allow_redirects=True, '
        'proxies=None, hooks=None, stream=None, verify=None, cert=None, '

Next, we built a factory function with_method that creates new functions which make HTTP requests with the proper HTTP verb. Because the method parameter is bound, it won’t show up it is removed from the resulting functions signature. Of course, the signature of these generated functions remains explicit, let’s try it out:

response = get('')
assert 'Feeling Lucky' in response.text

You can review the alternate code (the actual implementation) by visiting the code for requests.api.

Indices and tables

Project information

forge is released under the MIT license, its documentation lives at Read the Docs, the code on GitHub, and the latest release on PyPI. It’s rigorously tested on Python 3.6+ and PyPy 3.5+.

forge is authored by Devin Fee. Other contributors are listed under