Decompressing a file retrieved by URL seems too complex

[John Nagle]

(Repost with better indentation)
I'm reading a URL which is a .gz file, and decompressing
it. This works, but it seems far too complex. Yet
none of the "wrapping" you might expect to work
actually does. You can't wrap a GzipFile around
an HTTP connection, because GzipFile, reasonably enough,
needs random access, and tries to do "seek" and "tell".
Nor is the output descriptor from gzip general; it fails
on "readline", but accepts "read". (No good reason
for that.) So I had to make a second copy.

John Nagle

def readurl(url) :
if url.endswith(".gz") :
nd = urllib2.urlopen(url,timeout=TIMEOUTSECS)
td1 = tempfile.TemporaryFile() # compressed file
td1.write(nd.read()) # fetch and copy file
nd.close() # done with network
td2 = tempfile.TemporaryFile() # decompressed file
td1.seek(0) # rewind
gd = gzip.GzipFile(fileobj=td1, mode="rb") # wrap unzip
td2.write(gd.read()) # decompress file
td1.close() # done with compressed copy
td2.seek(0) # rewind
return(td2) # return file object for compressed object
else :
return(urllib2.urlopen(url,timeout=TIMEOUTSECS))

 

[Thomas Jollans]

(Repost with better indentation)

Good, good.

def readurl(url) :
if url.endswith(".gz") :

The file name could be anything. You should be checking the reponse Content-
Type header -- that's what it's for.

nd = urllib2.urlopen(url,timeout=TIMEOUTSECS)
td1 = tempfile.TemporaryFile() # compressed file

You can keep the whole thing in memory by using StringIO.

td1.write(nd.read()) # fetch and copy file

You're reading the entire fire into memory anyway ;-)

nd.close() # done with network
td2 = tempfile.TemporaryFile() # decompressed file

Okay, maybe there is somthing missing from GzipFile -- but still you could use
StringIO again, I expect.

Nor is the output descriptor from gzip general; it fails
on "readline", but accepts "read".

What exactly is it that's failing, and how?

 

[Aahz]

I'm reading a URL which is a .gz file, and decompressing it. This
works, but it seems far too complex. Yet none of the "wrapping"
you might expect to work actually does. You can't wrap a GzipFile
around an HTTP connection, because GzipFile, reasonably enough, needs
random access, and tries to do "seek" and "tell". Nor is the output
descriptor from gzip general; it fails on "readline", but accepts
"read". (No good reason for that.) So I had to make a second copy.

Also consider using zlib directly.