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Uncompressing a .Z file with Python

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3

1

I'm trying to uncompress a *.Z file using Python. I downloaded it via FTP (binary mode). The file successfully uncompresses with 7zip (whose "info" on the file says it's of type "Z"). The original file can be found at ftp://cddis.gsfc.nasa.gov/gps/products/1860/igr18600.sp3.Z.

I've read up on the use of the zlib module in Python and have some test code I'm using:

import zlib

comp_data = open('C:Tempigr18600.sp3.Z', 'rb').read()

print(comp_data[0:10])

uncomp_data = zlib.decompress(comp_data)
with open('c:tempigr18600.sp3', 'wb') as f:
 f.write(uncomp_data)
 f.close()

When I execute this I get the following output:

b'x1fx9dx90#xc6@x91x01#F'
Traceback (most recent call last):
 File "test.py", line 7, in <module>
 uncomp_data = zlib.decompress(comp_data)
zlib.error: Error -3 while decompressing data: incorrect header check

zlib clearly doesn't like the header. The first couple of bytes appear to match the proper magic number sequence 0x1F9d for a compressed file (per https://en.wikipedia.org/wiki/List_of_file_signatures).

In a pinch I can work around this by shelling out to 7zip directly. But I was hoping to find a pure Python type of answer. Despite spending most of the day googling for an answer (or this error message) I haven't had much luck. Perhaps my search skills are atrophying?

python zlib compression

share|improve this question

edited Oct 3 '15 at 10:54

mpromonet

6,9701010 gold badges3939 silver badges6868 bronze badges

asked Oct 3 '15 at 10:02

Tom JohnsonTom Johnson

91711 gold badge77 silver badges2222 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  The link also mentions about 7-Zip File Format as 37 7A BC AF 27 1C.
  
  – Fredrick Gauss
  Oct 3 '15 at 10:57
  

  
  
  
  

add a comment | 

3

1

I'm trying to uncompress a *.Z file using Python. I downloaded it via FTP (binary mode). The file successfully uncompresses with 7zip (whose "info" on the file says it's of type "Z"). The original file can be found at ftp://cddis.gsfc.nasa.gov/gps/products/1860/igr18600.sp3.Z.

I've read up on the use of the zlib module in Python and have some test code I'm using:

import zlib

comp_data = open('C:Tempigr18600.sp3.Z', 'rb').read()

print(comp_data[0:10])

uncomp_data = zlib.decompress(comp_data)
with open('c:tempigr18600.sp3', 'wb') as f:
 f.write(uncomp_data)
 f.close()

When I execute this I get the following output:

b'x1fx9dx90#xc6@x91x01#F'
Traceback (most recent call last):
 File "test.py", line 7, in <module>
 uncomp_data = zlib.decompress(comp_data)
zlib.error: Error -3 while decompressing data: incorrect header check

zlib clearly doesn't like the header. The first couple of bytes appear to match the proper magic number sequence 0x1F9d for a compressed file (per https://en.wikipedia.org/wiki/List_of_file_signatures).

In a pinch I can work around this by shelling out to 7zip directly. But I was hoping to find a pure Python type of answer. Despite spending most of the day googling for an answer (or this error message) I haven't had much luck. Perhaps my search skills are atrophying?

python zlib compression

share|improve this question

edited Oct 3 '15 at 10:54

mpromonet

6,9701010 gold badges3939 silver badges6868 bronze badges

asked Oct 3 '15 at 10:02

Tom JohnsonTom Johnson

91711 gold badge77 silver badges2222 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  The link also mentions about 7-Zip File Format as 37 7A BC AF 27 1C.
  
  – Fredrick Gauss
  Oct 3 '15 at 10:57
  

  
  
  
  

add a comment | 

I'm trying to uncompress a *.Z file using Python. I downloaded it via FTP (binary mode). The file successfully uncompresses with 7zip (whose "info" on the file says it's of type "Z"). The original file can be found at ftp://cddis.gsfc.nasa.gov/gps/products/1860/igr18600.sp3.Z.

I've read up on the use of the zlib module in Python and have some test code I'm using:

import zlib

comp_data = open('C:Tempigr18600.sp3.Z', 'rb').read()

print(comp_data[0:10])

uncomp_data = zlib.decompress(comp_data)
with open('c:tempigr18600.sp3', 'wb') as f:
 f.write(uncomp_data)
 f.close()

When I execute this I get the following output:

b'x1fx9dx90#xc6@x91x01#F'
Traceback (most recent call last):
 File "test.py", line 7, in <module>
 uncomp_data = zlib.decompress(comp_data)
zlib.error: Error -3 while decompressing data: incorrect header check

zlib clearly doesn't like the header. The first couple of bytes appear to match the proper magic number sequence 0x1F9d for a compressed file (per https://en.wikipedia.org/wiki/List_of_file_signatures).

In a pinch I can work around this by shelling out to 7zip directly. But I was hoping to find a pure Python type of answer. Despite spending most of the day googling for an answer (or this error message) I haven't had much luck. Perhaps my search skills are atrophying?

python zlib compression

share|improve this question

edited Oct 3 '15 at 10:54

mpromonet

6,9701010 gold badges3939 silver badges6868 bronze badges

asked Oct 3 '15 at 10:02

Tom JohnsonTom Johnson

91711 gold badge77 silver badges2222 bronze badges

import zlib

comp_data = open('C:Tempigr18600.sp3.Z', 'rb').read()

print(comp_data[0:10])

uncomp_data = zlib.decompress(comp_data)
with open('c:tempigr18600.sp3', 'wb') as f:
 f.write(uncomp_data)
 f.close()

b'x1fx9dx90#xc6@x91x01#F'
Traceback (most recent call last):
 File "test.py", line 7, in <module>
 uncomp_data = zlib.decompress(comp_data)
zlib.error: Error -3 while decompressing data: incorrect header check

share|improve this question

edited Oct 3 '15 at 10:54

mpromonet

6,9701010 gold badges3939 silver badges6868 bronze badges

asked Oct 3 '15 at 10:02

Tom JohnsonTom Johnson

91711 gold badge77 silver badges2222 bronze badges

share|improve this question

edited Oct 3 '15 at 10:54

mpromonet

6,9701010 gold badges3939 silver badges6868 bronze badges

asked Oct 3 '15 at 10:02

Tom JohnsonTom Johnson

91711 gold badge77 silver badges2222 bronze badges

edited Oct 3 '15 at 10:54

mpromonet

6,9701010 gold badges3939 silver badges6868 bronze badges

edited Oct 3 '15 at 10:54

mpromonet

6,9701010 gold badges3939 silver badges6868 bronze badges

asked Oct 3 '15 at 10:02

Tom JohnsonTom Johnson

91711 gold badge77 silver badges2222 bronze badges

asked Oct 3 '15 at 10:02

Tom JohnsonTom Johnson

91711 gold badge77 silver badges2222 bronze badges

1 Answer
1

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4

Python does not have the equivalent of Unix uncompress available in a module, which is what you'd need to decompress a .Z file. You would either need to a) shell out to the Unix compress command, b) shell out to gzip, c) shell out to 7-zip (both gzip and 7-zip have the ability to decompress .Z files), d) modify the original uncompress code in C and link that to Python (the code is available online), or e) write your own LZW decompressor in native Python.

For d), you can find some C code I wrote to do this job in this answer on mathematica.stackexchange.com. See the unlzw() function.

share|improve this answer

edited Apr 13 '17 at 12:55

Community♦

111 silver badge

answered Oct 3 '15 at 15:39

Mark AdlerMark Adler

61.9k88 gold badges7272 silver badges115115 bronze badges

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Thanks Mark. Appreciate all your hard work on zlib. Good to hear I wasn't missing something obvious. I'll shell out to 7-zip for now and begin investigating d and e for my own edification.
  
  – Tom Johnson
  Oct 4 '15 at 11:00
  

  
  
  
  


• 
  
  
  

  
  4
  

  
  
  
  
  
  

  
  
  I went with option e. Thanks for your help, Mark. github.com/umeat/unlzw
  
  – unclemeat
  May 26 '16 at 0:18
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @unclemeat, thanks for tackling the pure python implementation. I'll give your's a try for my application as well.
  
  – Tom Johnson
  Jul 7 '16 at 14:12
  

  
  
  
  

add a comment | 

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4

Python does not have the equivalent of Unix uncompress available in a module, which is what you'd need to decompress a .Z file. You would either need to a) shell out to the Unix compress command, b) shell out to gzip, c) shell out to 7-zip (both gzip and 7-zip have the ability to decompress .Z files), d) modify the original uncompress code in C and link that to Python (the code is available online), or e) write your own LZW decompressor in native Python.

For d), you can find some C code I wrote to do this job in this answer on mathematica.stackexchange.com. See the unlzw() function.

share|improve this answer

edited Apr 13 '17 at 12:55

Community♦

111 silver badge

answered Oct 3 '15 at 15:39

Mark AdlerMark Adler

61.9k88 gold badges7272 silver badges115115 bronze badges

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Thanks Mark. Appreciate all your hard work on zlib. Good to hear I wasn't missing something obvious. I'll shell out to 7-zip for now and begin investigating d and e for my own edification.
  
  – Tom Johnson
  Oct 4 '15 at 11:00
  

  
  
  
  


• 
  
  
  

  
  4
  

  
  
  
  
  
  

  
  
  I went with option e. Thanks for your help, Mark. github.com/umeat/unlzw
  
  – unclemeat
  May 26 '16 at 0:18
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @unclemeat, thanks for tackling the pure python implementation. I'll give your's a try for my application as well.
  
  – Tom Johnson
  Jul 7 '16 at 14:12
  

  
  
  
  

add a comment | 

4

Python does not have the equivalent of Unix uncompress available in a module, which is what you'd need to decompress a .Z file. You would either need to a) shell out to the Unix compress command, b) shell out to gzip, c) shell out to 7-zip (both gzip and 7-zip have the ability to decompress .Z files), d) modify the original uncompress code in C and link that to Python (the code is available online), or e) write your own LZW decompressor in native Python.

For d), you can find some C code I wrote to do this job in this answer on mathematica.stackexchange.com. See the unlzw() function.

share|improve this answer

edited Apr 13 '17 at 12:55

Community♦

111 silver badge

answered Oct 3 '15 at 15:39

Mark AdlerMark Adler

61.9k88 gold badges7272 silver badges115115 bronze badges

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Thanks Mark. Appreciate all your hard work on zlib. Good to hear I wasn't missing something obvious. I'll shell out to 7-zip for now and begin investigating d and e for my own edification.
  
  – Tom Johnson
  Oct 4 '15 at 11:00
  

  
  
  
  


• 
  
  
  

  
  4
  

  
  
  
  
  
  

  
  
  I went with option e. Thanks for your help, Mark. github.com/umeat/unlzw
  
  – unclemeat
  May 26 '16 at 0:18
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @unclemeat, thanks for tackling the pure python implementation. I'll give your's a try for my application as well.
  
  – Tom Johnson
  Jul 7 '16 at 14:12
  

  
  
  
  

add a comment | 

Python does not have the equivalent of Unix uncompress available in a module, which is what you'd need to decompress a .Z file. You would either need to a) shell out to the Unix compress command, b) shell out to gzip, c) shell out to 7-zip (both gzip and 7-zip have the ability to decompress .Z files), d) modify the original uncompress code in C and link that to Python (the code is available online), or e) write your own LZW decompressor in native Python.

For d), you can find some C code I wrote to do this job in this answer on mathematica.stackexchange.com. See the unlzw() function.

share|improve this answer

edited Apr 13 '17 at 12:55

Community♦

111 silver badge

answered Oct 3 '15 at 15:39

Mark AdlerMark Adler

61.9k88 gold badges7272 silver badges115115 bronze badges

share|improve this answer

edited Apr 13 '17 at 12:55

Community♦

111 silver badge

answered Oct 3 '15 at 15:39

Mark AdlerMark Adler

61.9k88 gold badges7272 silver badges115115 bronze badges

edited Apr 13 '17 at 12:55

Community♦

111 silver badge

edited Apr 13 '17 at 12:55

Community♦

111 silver badge

answered Oct 3 '15 at 15:39

Mark AdlerMark Adler

61.9k88 gold badges7272 silver badges115115 bronze badges

answered Oct 3 '15 at 15:39

Mark AdlerMark Adler

61.9k88 gold badges7272 silver badges115115 bronze badges