rename_arguments creates double-partial when input is functools.partial

[hmgaudecker]

Bug

rename_arguments creates a double-partial when the input function is a functools.partial, causing the bound positional arguments to be passed twice.

Minimal Reproducible Example

import functools
from dags.signature import rename_arguments

def inner(bound_arg, free_arg):
    return f"bound={bound_arg}, free={free_arg}"

func = functools.partial(inner, "BOUND_VALUE")

renamed = rename_arguments(func, mapper={"free_arg": "renamed_free"})

renamed(renamed_free="hello")
# TypeError: inner() got multiple values for argument 'free_arg'

renamed("hello")
# TypeError: inner() takes 2 positional arguments but 3 were given

Root Cause

In dags/signature.py, rename_arguments lines 274-279:

# Preserve function type
if isinstance(func, functools.partial):
    partial_wrapper = functools.partial(
        wrapper_rename_arguments, *func.args, **func.keywords
    )
    out = cast("Callable[P, R]", partial_wrapper)

wrapper_rename_arguments already captures func (the partial) in its closure and delegates to it via func(*args, **internal_kwargs). The bound args from the partial are already applied when func is called internally.

The "Preserve function type" block then wraps wrapper_rename_arguments in another functools.partial with the same *func.args, so those args get passed twice: once by the outer partial as positional args, and once by the inner func() call (which is the original partial).

Expected Behavior

rename_arguments should work correctly with functools.partial inputs — renaming only the free (unbound) parameters without duplicating the bound arguments.

dags Version

0.5.0 (also affects current main)