compression.zstd.open() names the wrong mode in its invalid mode error #161730

Bug report

Bug description:

compression.zstd.open() rejects a mode that contains both 't' and 'b', but the error message names a different mode than the one passed:

>>> import io
>>> from compression import zstd
>>> zstd.open(io.BytesIO(zstd.compress(b'x')), 'rtb')
Traceback (most recent call last):
  ...
ValueError: Invalid mode: 'rb'

'rb' is a valid mode. open() removes 't' from the mode before checking for 'b', and the message is formatted with the modified string:

text_mode = 't' in mode
mode = mode.replace('t', '')

if text_mode:
    if 'b' in mode:
        raise ValueError(f'Invalid mode: {mode!r}')

gzip.open(), bz2.open() and lzma.open() report the mode as passed (Invalid mode: 'rtb').

CPython versions tested on:

3.14, 3.15, CPython main branch

Operating systems tested on:

Linux

Linked PRs

• gh-161730: Fix the mode in the compression.zstd.open() invalid mode error #161731