zlib.decompress fails, zlib.decompressobj succeeds - bug or feature?

[Matthew Brett]

Hi,

I sorry if this is a bad place to ask, but I wanted to find out if the
behavior I'm seeing is a bug.

I maintain scipy's matlab file readers, and I came across a zlib
compressed string that causes a zlib error on decompression, but only
with zlib.decompress, not zlib.decompressobj.

I saved the original compressed string as a binary file at
http://dl.dropbox.com/u/794947/mat.bin

Now if I do:

import zlib
data = open('mat.bin', 'rb').read()
out = zlib.decompress(data)

I get an error : Error -5 while decompressing data)

If instead I do this:

out = zlib.decompressobj().decompress(data)

I get a usable uncompressed string. I was expecting these two calls
to do the same thing. Is that expectation right? If not, is there
somewhere I could find out why?

Thanks a lot,

Matthew

 

[Antoine Pitrou]

If instead I do this:

out = zlib.decompressobj().decompress(data)

How about:

d = zlib.decompressobj()
out = d.decompress(data) + d.flush()

?

Notice the documentation for decompressobj.decompress (emphasis mine):

“Decompress string, returning a string containing the uncompressed data
corresponding to *at least part* of the data in stringâ€.

 

[Matthew Brett]

Hi,

Thanks for the reply.

How about:

d = zlib.decompressobj()
out = d.decompress(data) + d.flush()

Do you mean, that you would then expect the decompressobj method to
fail as well?

But, no, d.flush() returns the empty string after decompressing
``data``.

Thanks again,

Matthew

 

[Antoine Pitrou]

Do you mean, that you would then expect the decompressobj method to
fail as well?
Yes.

But, no, d.flush() returns the empty string after decompressing
``data``.

Hmm, then it's a bug. Can you report it to http://bugs.python.org ?

Thank you

Antoine.

 

[Matthew Brett]

Hi,

Hmm, then it's a bug. Can you report it tohttp://bugs.python.org?

I will - thanks for your advice,

Matthew