[NotorandXor256]

Fixes #161004
This PR fix functools.reduce.The C functools_reduce calls PyObject_GetIter(seq) once and then only PyIter_Next(it). The Python version calls iter(sequence) and then for element in it:, which calls iter() again on the iterator.

this PR fix this behavior by change for loop for element in it: to while loop. While loop is terminated next(element) throw a StopIteration exception and error handle it and break the loop

this PR also add a test and change the documentation

• Issue: Pure-Python functools.reduce calls iter() twice, unlike the C implementation #161004

[bedevere-app]

Most changes to Python require a NEWS entry. Add one using the blurb_it web app or the blurb command-line tool.

If this change has little impact on Python users, wait for a maintainer to apply the skip news label instead.

[read-the-docs-community]

Documentation build overview

📚 cpython-previews | 🛠️ Build #35548826 | 📁 Comparing deb5f70 against main (683fca8)

  🔍 Preview build  

1 file changed

± library/functools.html

[picnixz]

Suggested change

	while(True):
	while True:

I don't really think it's necessary to change this though as it's a "roughly equivalent" code.

[picnixz]

Suggested change

	try:
	element = next(it)
	except StopIteration:
	# Stop when no elements are left
	break
	try:
	element = next(it)
	except StopIteration:
	break

[picnixz]

Suggested change

	while(True):
	# Mirror the C implementation which calls sequence.__iter__() only once.
	while True:

[picnixz]

Add this test in test_functools.py instead.

[picnixz]

Keep that new line.

[rhettinger]

I wouldn't make this edit. As noted in the issue, the iterator protocol specifically allows this. Also, this code is a "rough equivalent" intended to communicate the concept of what reduce does.