Grant said:
Doh! I misread your post and thought were weren't getting a
warm fuzzying feeling _because_ it was doing a byte-byte
compare. Now I'm a bit confused. Are you under the impression
it's _not_ doing a byte-byte compare? Here's the code:
def _do_cmp(f1, f2):
bufsize = BUFSIZE
fp1 = open(f1, 'rb')
fp2 = open(f2, 'rb')
while True:
b1 = fp1.read(bufsize)
b2 = fp2.read(bufsize)
if b1 != b2:
return False
if not b1:
return True
It looks like a byte-by-byte comparison to me. Note that when
this function is called the file lengths have already been
compared and found to be equal.
But there's a cache. A change of file contents may go undetected as long as
the file stats don't change:
$ cat fool_filecmp.py
import filecmp, shutil, sys
for fn in "adb":
with open(fn, "w") as f:
f.write("yadda")
shutil.copystat("d", "a")
filecmp.cmp("a", "b", False)
with open("a", "w") as f:
f.write("*****")
shutil.copystat("d", "a")
if "--clear" in sys.argv:
print "clearing cache"
filecmp._cache.clear()
if filecmp.cmp("a", "b", False):
print "file a and b are equal"
else:
print "file a and b differ"
print "a's contents:", open("a").read()
print "b's contents:", open("b").read()
$ python2.6 fool_filecmp.py
file a and b are equal
a's contents: *****
b's contents: yadda
Oops. If you are paranoid you have to clear the cache before doing the
comparison:
$ python2.6 fool_filecmp.py --clear
clearing cache
file a and b differ
a's contents: *****
b's contents: yadda
Peter
