Python Function Signatures (funcsigs)

1.0.2 · maintenance · verified Thu Apr 09

funcsigs is a Python library that backports the function signature introspection features from Python 3.3's `inspect` module (PEP 362) to older Python versions. It allows developers to work with `Signature` and `Parameter` objects to understand callable arguments and return annotations, even in Python 2.6, 2.7, and 3.2+. Its latest version, 1.0.2, was released in April 2016, marking it as a mature and largely unmaintained project, as its core functionality has been integrated into Python's standard library for modern versions.

Warnings

gotcha For Python 3.3 and newer, the built-in `inspect.signature` should be used instead of `funcsigs.signature`. Relying on `funcsigs` in newer Python versions is unnecessary and can introduce compatibility issues if the native `inspect` module's behavior changes or if `funcsigs` is not installed.
Fix: Use `from inspect import signature` instead of `from funcsigs import signature` when targeting Python 3.3 or newer. For projects needing broad compatibility, consider a conditional import: `try: from inspect import signature except ImportError: from funcsigs import signature`.
deprecated The `funcsigs` library is no longer actively maintained since its functionality has been integrated into the Python standard library's `inspect` module (from Python 3.3 onwards). While functional for its intended older Python versions, new development should prefer `inspect.signature`.
Fix: Migrate to `inspect.signature` for Python 3.3+ projects. For projects requiring Python 2.x or 3.2 compatibility, `funcsigs` remains a valid option, but be aware of its unmaintained status.
gotcha Compatibility quirks exist in specific environments: in Python 2.x, issues can arise when a function is assigned to a class's `__wrapped__` property after construction. Under PyPy, directly passing the `__call__` method of a builtin can also cause compatibility problems.
Fix: Be aware of these specific edge cases when using `funcsigs` in Python 2.x or PyPy, and test thoroughly. Avoid directly manipulating `__wrapped__` on classes or passing `__call__` of builtins directly if issues are encountered.

Install

pip install funcsigs Install latest version

Imports

signature
```
from funcsigs import signature
```
The inspect module in Python 2.x and Python < 3.3 does not have `signature`. This is the core reason to use funcsigs.
Signature
```
from funcsigs import Signature
```
Parameter
```
from funcsigs import Parameter
```

Quickstart

This example demonstrates how to obtain a Signature object for a function, inspect its parameters, and access type annotations (where applicable).

from funcsigs import signature

def foo(a, b=None, *args, **kwargs):
    pass

sig = signature(foo)
print(f"Signature: {sig}")
print(f"Parameters: {sig.parameters}")

def bar(x: int, y: str = 'default') -> bool:
    pass

sig_bar = signature(bar)
print(f"Signature (with annotations): {sig_bar}")
print(f"Return annotation: {sig_bar.return_annotation}")

view raw JSON →