Add `seekable` method for `mmap.mmap`

[technillogue]

Bug report

Bug description:

mmap.mmap has a seek() method, but no seekable() method. Because of this, it cannot be used an argument for ZipFile, which requires a file-like object with seekable. A small patch is enough to fix this

class SeekableMmap(mmap.mmap):
    def seekable(self):
        return True

Now SeekableMmap can be passed to ZipFile without issue. It's easy to fix, but I can't think of any reasons why mmap shouldn't have a seekable method.

CPython versions tested on:

3.8, 3.11

Operating systems tested on:

Linux

Linked PRs

• gh-111835: Add seekable method to mmap.mmap #111852
• pythongh-111835: Add seekable method to mmap.mmap #111865

[serhiy-storchaka]

mmap.seek() returns None. The seek() method of other file-like objects return the new file position. Would not it cause issues?

[technillogue]

I also opened a PR #111865 for this, I just took a while between pushing the code and opening the PR.

[corona10]

mmap.seek() returns None. The seek() method of other file-like objects return the new file position. Would not it cause issues?

Yeah, in that case, we can make a seek() method to return where value. It will break the user's code actually?
In my naive idea, people cannot do something with None value.