mirror of
https://github.com/python/cpython.git
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4acc25bd39
1. Comments at the beginning of the module, before
functions, and before classes have been turned
into docstrings.
2. Tabs are normalized to four spaces.
Also, removed the "remove" function from dircmp.py, which reimplements
list.remove() (it must have been very old).
64 lines
2 KiB
Python
64 lines
2 KiB
Python
"""Efficiently compare files, boolean outcome only (equal / not equal).
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Tricks (used in this order):
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- Use the statcache module to avoid statting files more than once
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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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"""
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import os
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from stat import *
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import statcache
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# The cache.
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#
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cache = {}
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def cmp(f1, f2, shallow=1):
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"""Compare two files, use the cache if possible.
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May raise os.error if a stat or open of either fails.
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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(statcache.stat(f1)), sig(statcache.stat(f2))
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if not S_ISREG(s1[0]) or not S_ISREG(s2[0]):
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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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if cache.has_key(key):
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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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# 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):
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"""Return signature (i.e., type, size, mtime) from raw stat data."""
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return S_IFMT(st[ST_MODE]), st[ST_SIZE], st[ST_MTIME]
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def do_cmp(f1, f2):
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"""Compare two files, really."""
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#print ' cmp', f1, f2 # XXX remove when debugged
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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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