I justed optimized partial_call() for positional arguments in the change c1a698edfa1b to avoid the creation of a temporary tuple when possible.

I noticed that keyword parameters from partial() constructor are always copied. Is it mandatory? Can't we avoid copying them?

Example:
---
import functools
hello = functools.partial(print, "Hello World", end='!\n')
hello()
---

hello keyword arguments are {'end'; '!\n'}.

Attached patch avoids copying keyword arguments when the partial objects is not called with new keyword arguments.

Tests pass, but I don't know if there is a risk that some strange function modify keyword arguments in-place?

Modifying the keyword arguments dict is quite common so this change would be a heavy compatibility breaker.

A well-known idiom:

  def some_function(..., **kwargs):
      some_option = kwargs.pop('some_option', None)
      # further process kwargs

I concur with Antoine.

Ah yes sorry, I misunderstood the link between kwargs from a C function and
a PY function. The link is simple, it's the same object :-) This issue can
be closed.

I reopen the issue to propose to add a comment explaining why the dictionary must always be copied:
https://github.com/python/cpython/pull/253

PR 253 has been merged.