The zlib module doesn't support raw deflate format, so it doesn't
completely interoperate with php's "gzdeflate" function and fails to
decompress some strings that web browsers can decompress.

A workaround is to use a special zlib feature and pass the value -15 as
the "wbits" arg: 

plaintext = zlib.deflate(compressed_text, wbits=-15)

I don't know if it's appropriate to mess with the code, but at minimum I
urge that the workaround be mentioned in the docs.  We had a tremendous
distruption where I work because of a malicious raw-deflated PHP script
that we couldn't decompress with Python for analysis.  We had to resort
to decompressing in a PHP container that (through my slipping up) it
proceeded to escape from.  

Help us Python-Kenobi, save us from PHP ;-)

I should have mentioned, the docs do say "When wbits is negative, the
standard gzip header is suppressed; this is an undocumented feature of
the zlib library, used for compatibility with unzip‘s compression file
format" but this wasn't enough at the time to figure out the issue.  I
suggest adding something like "and the 'raw deflate' format supported by
PHP and some web browsers.  

I better see if I can research the exact situation a bit further, for
the sake of documenting it accurately, if others here think it's a good
idea.

A doc addition would seem like a good idea, so I am changing this to a doc issue for the current versions. Can you suggest specific text and a specific location to place it?

A behavior change could only go into 3.2. I do not know who, if anyone, maintains zlib. A reference to the desired algorithm might be necessary.