user3820991 user3820991 - 6 months ago 377
Python Question

python extract uncompressed data from 7z-file

I have several csv-files, some of which are compressed but others are not, all in a 7z archive. I want to read the csv files and save the content in a database. However, whenever py7zlib attemts to read the data from a csv file that is actually not compressed, I get the error

data error during decompression
.

import os
import py7zlib

scr = r'Y:\PathtoArchive'
z7file = 'ArchiveName.7z'

with open(os.path.join(scr,z7file),'rb') as f:
archive = py7zlib.Archive7z(f)

names = archive.filenames

for mem in names:

obj = archive.getmember(mem)
print obj.compressed # prints None for uncompressed data
try:
data = obj.read()
except Exception as er:
print er # prints data error during decompression
# whenever obj.compressed is None


The error happens in

File "C:\Anaconda\lib\site-packages\py7zlib.py", line 608, in read
data = getattr(self, decoder)(coder, data, level)
File "C:\Anaconda\lib\site-packages\py7zlib.py", line 671, in _read_lzma
return self._read_from_decompressor(coder, dec, input, level, checkremaining=True, with_cache=True)
File "C:\Anaconda\lib\site-packages\py7zlib.py", line 646, in _read_from_decompressor
tmp = decompressor.decompress(data)
ValueError: data error during decompression


So, how can I extract uncompressed data from a 7z-Archive?

Answer

Though I couldn't really figure out what the problem seemed to be, I found a workaround that solved the ultimate goal to obtain the data from csv-files from a 7z-archive. 7-zip comes with a command line tool. Communicating with that tool via the subprocess module, I could automatically extract the files that I wihsed to extract without any problems

import subprocess
import py7zlib 

archiveman = r'c:\Program Files\7-zip\7z' # 7z.exe comes with 7-zip
archivepath = r'C:\Path\to\archive.7z'

with open(archivepath,'rb') as f:
    archive = py7zlib.Archive7z(f)
    names = archive.filenames
    for name in names:
        _ = subprocess.check_output([archiveman, 'e', archivepath, '-o{}'.format(r'C:\Destination\of\copy'), name])

The different commands that can be used with 7z can be found here.