binary mode doesn't take an encoding argument

[yaythomas]

The actual open() function does not allow you to pass an encoding when in binary mode:

>>> open('filename', 'wb', encoding='utf-8')
ValueError: binary mode doesn't take an encoding argument
>>> open('arb', 'b', encoding='utf-8')
ValueError: binary mode doesn't take an encoding argument

Assuming this is not an intentional divergence from open() behaviour, I think the fix would be to insert this:

if binary and encoding:
    raise ValueError("binary mode doesn't take an encoding argument")

just after here:
https://github.com/jmcgeheeiv/pyfakefs/blob/4dc8615957dadfc64d6a8f864ee93c7c65da38b5/pyfakefs/fake_filesystem.py#L5574

Before I prepare a PR, I thought I'd ask whether you think this is suitable first?

P.S this is an AMAZING project - it's my favourite new thing in my tool-belt! Thank you so much for all the work and care that went into this complex wonderful beast!

[mrbean-bremen]

Thanks :) And good catch - no, this wasn't meant to diverge, we just overlooked it.
You mean if its a suitable first PR? Sure, go ahead!

[yaythomas]

By suitable I meant more whether my suggested simplistic fix was comically naive and unaware of other complexities :-)

PR incoming. . .

[mrbean-bremen]

The test coverage is pretty ok here, so it is not very likely that you will break something if the tests pass. And I guess you will add a test of your own for the change...

[mrbean-bremen]

Thank you, nice work!

[yaythomas]

Pleasure was mine! Thanks for a smooth contribution experience!