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https://github.com/python/cpython
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3aa9ca147b
1. Fix incorrect file open mode on Win32 platforms (use "rb" instead of "r"). 2. Add shallow parameter to cmp.cmp(). If false, deep file comparisons are made. The module should be 100 percent backwards compatible.
62 lines
1.7 KiB
Python
62 lines
1.7 KiB
Python
# Module 'cmp'
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# Efficiently compare files, boolean outcome only (equal / not equal).
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# Tricks (used in this order):
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# - Files with identical type, size & mtime are assumed to be clones
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# - Files with different type or size cannot be identical
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# - We keep a cache of outcomes of earlier comparisons
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# - We don't fork a process to run 'cmp' but read the files ourselves
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import os
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cache = {}
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def cmp(f1, f2, shallow=1): # Compare two files, use the cache if possible.
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# Return 1 for identical files, 0 for different.
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# Raise exceptions if either file could not be statted, read, etc.
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s1, s2 = sig(os.stat(f1)), sig(os.stat(f2))
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if s1[0] <> 8 or s2[0] <> 8:
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# Either is a not a plain file -- always report as different
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return 0
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if shallow and s1 == s2:
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# type, size & mtime match -- report same
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return 1
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if s1[:2] <> s2[:2]: # Types or sizes differ, don't bother
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# types or sizes differ -- report different
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return 0
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# same type and size -- look in the cache
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key = (f1, f2)
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try:
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cs1, cs2, outcome = cache[key]
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# cache hit
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if s1 == cs1 and s2 == cs2:
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# cached signatures match
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return outcome
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# stale cached signature(s)
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except KeyError:
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# cache miss
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pass
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# really compare
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outcome = do_cmp(f1, f2)
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cache[key] = s1, s2, outcome
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return outcome
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def sig(st): # Return signature (i.e., type, size, mtime) from raw stat data
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# 0-5: st_mode, st_ino, st_dev, st_nlink, st_uid, st_gid
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# 6-9: st_size, st_atime, st_mtime, st_ctime
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type = st[0] / 4096
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size = st[6]
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mtime = st[8]
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return type, size, mtime
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def do_cmp(f1, f2): # Compare two files, really
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bufsize = 8*1024 # Could be tuned
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fp1 = open(f1, 'rb')
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fp2 = open(f2, 'rb')
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while 1:
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b1 = fp1.read(bufsize)
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b2 = fp2.read(bufsize)
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if b1 <> b2: return 0
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if not b1: return 1
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