python分割文件的常用方法(2)

#!/usr/bin/python
##########################################################################
# split a file into a set of parts; join.py puts them back together;
# this is a customizable version of the standard unix split command-line
# utility; because it is written in Python, it also works on Windows and
# can be easily modified; because it exports a function, its logic can
# also be imported and reused in other applications;
##########################################################################
     
import sys, os
kilobytes = 1024
megabytes = kilobytes * 1000
chunksize = int(1.4 * megabytes)   # default: roughly a floppy
     
def split(fromfile, todir, chunksize=chunksize):
    if not os.path.exists(todir):  # caller handles errors
os.mkdir(todir)    # make dir, read/write parts
    else:
for fname in os.listdir(todir):    # delete any existing files
    os.remove(os.path.join(todir, fname))
    partnum = 0
    input = open(fromfile, 'rb')   # use binary mode on Windows
    while 1:       # eof=empty string from read
chunk = input.read(chunksize)      # get next part <= chunksize
if not chunk: break
partnum  = partnum+1
filename = os.path.join(todir, ('part%04d' % partnum))
fileobj  = open(filename, 'wb')
fileobj.write(chunk)
fileobj.close()    # or simply open().write()
    input.close()
    assert partnum <= 9999 # join sort fails if 5 digits
    return partnum
    
if __name__ == '__main__':
    if len(sys.argv) == 2 and sys.argv[1] == '-help':
print 'Use: split.py [file-to-split target-dir [chunksize]]'
    else:
if len(sys.argv) < 3:
    interactive = 1
    fromfile = raw_input('File to be split? ')       # input if clicked
    todir    = raw_input('Directory to store part files? ')
else:
    interactive = 0
    fromfile, todir = sys.argv[1:3]  # args in cmdline
    if len(sys.argv) == 4: chunksize = int(sys.argv[3])
absfrom, absto = map(os.path.abspath, [fromfile, todir])
print 'Splitting', absfrom, 'to', absto, 'by', chunksize
     
try:
    parts = split(fromfile, todir, chunksize)
except:
    print 'Error during split:'
    print sys.exc_info()[0], sys.exc_info()[1]
else:
    print 'Split finished:', parts, 'parts are in', absto
if interactive: raw_input('Press Enter key') # pause if clicked