The docstring of struct.unpack currently reads

Unpack from the buffer buffer (presumably packed by pack(fmt, ...)) according to the format string fmt. The result is a tuple even if it contains exactly one item. The buffer must contain exactly the amount of data required by the format (len(bytes) must equal calcsize(fmt)).

It should probably read "len(buffer) must equal calcsize(fmt)".

I would remove "len(bytes) must equal " at all. len() can return a value not equal to the number of bytes contained in the buffer (e.g. for array('I')).

I think mentioning calcsize is still helpful, so perhaps something like
"The buffer must contain exactly as many bytes (I think this is clearer than "the amount of data") as required by the format (this number can be obtained as `struct.calcsize(fmt)`)"?  (and likewise for "unpack_from" and "iter_unpack").

That sounds good to me. Maybe without so many parentheses :)

Modified as suggested in the comments

Issue title: "Minor typo in the docs for struct.unpack"

I can say the same on issue26535.diff: there is a typo ;)

The patch looks good to me, though it should be applied to all three unpack functions and Struct methods, and the doc strings (struct.unpack.__doc__ etc).

An alternative wording is already used for struct.iter_unpack(): “the buffer’s size in bytes”. Maybe that is slightly clearer, but it’s no big deal.

The proposed wording looks fine.

Here is a new patch:

* Use “The buffer’s size in bytes” wording
* Avoid brackets inside brackets
* Fix the three unpack functions and corresponding methods
* Also fix doc strings

Seems you forgot to send a patch.

Indeed, let me try again

LGTM.

New changeset 7889fcb0697b by Martin Panter in branch '3.5':
Issue #26535: Correct docs regarding the struct buffer size
https://hg.python.org/cpython/rev/7889fcb0697b

New changeset 39dc2f39373d by Martin Panter in branch 'default':
Issue #26535: Merge struct doc from 3.5
https://hg.python.org/cpython/rev/39dc2f39373d