How to use the gzip module with the pickle module
I have a python program which creates a list of prime numbers [2L,3L,5L,7L,13L]. This program save the list to a file on the hard disk.
example of my code
fp=open('primes.data','r') # ListOfPrimes=[2L,3L,5L,7L] ListOfPrimes=cPickle.load(fp) fp.close() generate_more_primes() fp=open('primes.data','w') cPickle.dump(ListOfPrimes,fp) fp.close()
What I want
My problem is that the primes.data file is now 9 megabytes in size and I wanted to reduce the size taken by the file by first compressing the data with the gzip module before saving it. Hence I would also need to decompress the data after I read it from the file.
Any idea how I can do this?
lwickjr: I'd have to research for details, but you`d have to pickle the data to a string, then save the string to a file through gzip, and read the file from gzip into a string which is then unpickled.
MarcChr: There is no need for an temporary string. Just import gzip and use gzip.open instead of open:
import gzip, cPickle fp=gzip.open('primes.data','rb') # This assumes that primes.data is already packed with gzip ListOfPrimes=cPickle.load(fp) fp.close() generate_more_primes() fp=gzip.open('primes.data','wb') cPickle.dump(ListOfPrimes,fp) fp.close()
You could also use the binary pickle format which is more compact: cPickle.dump(ListOfPrimes,fp,1).
use this module gzippickle.py
"""Generic object pickler and compressor This module saves and reloads compressed representations of generic Python objects to and from the disk. Added Protocol field. """ __author__ = "Bill McNeill <firstname.lastname@example.org>" __version__ = "1.1" import pickle import gzip def save(object, filename, protocol = 0): """Saves a compressed object to disk """ file = gzip.GzipFile(filename, 'wb') file.write(pickle.dumps(object, protocol)) file.close() def load(filename): """Loads a compressed object from disk """ file = gzip.GzipFile(filename, 'rb') buffer = "" while True: data = file.read() if data == "": break buffer += data object = pickle.loads(buffer) file.close() return object if __name__ == "__main__": import sys import os.path class Object: x = 7 y = "This is an object." filename = sys.argv if os.path.isfile(filename): data = load(filename) z,l = data,data print "Loaded %s" % data print "z.x = %d z.y = %s" % (z.x,z.y) print "list = %s" % l else: z = Object() z.x = 666 l = [2,4,9] data = (z,l) save(data, filename) print "Saved %s" % data