difflib --- 計算差異的輔助工具¶

原始碼：Lib/difflib.py

This module provides classes and functions for comparing sequences. Itcan be used for example, for comparing files, and can produce informationabout file differences in various formats, including HTML and context and unifieddiffs. For comparing directories and files, see also, thefilecmp module.

classdifflib.SequenceMatcher

This is a flexible class for comparing pairs of sequences of any type, so longas the sequence elements arehashable. The basic algorithm predates, and is alittle fancier than, an algorithm published in the late 1980's by Ratcliff andObershelp under the hyperbolic name "gestalt pattern matching." The idea is tofind the longest contiguous matching subsequence that contains no "junk"elements; these "junk" elements are ones that are uninteresting in somesense, such as blank lines or whitespace. (Handling junk is anextension to the Ratcliff and Obershelp algorithm.) The sameidea is then applied recursively to the pieces of the sequences to the left andto the right of the matching subsequence. This does not yield minimal editsequences, but does tend to yield matches that "look right" to people.

Timing: The basic Ratcliff-Obershelp algorithm is cubic time in the worstcase and quadratic time in the expected case.SequenceMatcher isquadratic time for the worst case and has expected-case behavior dependent in acomplicated way on how many elements the sequences have in common; best casetime is linear.

Automatic junk heuristic:SequenceMatcher supports a heuristic thatautomatically treats certain sequence items as junk. The heuristic counts how manytimes each individual item appears in the sequence. If an item's duplicates (afterthe first one) account for more than 1% of the sequence and the sequence is at least200 items long, this item is marked as "popular" and is treated as junk forthe purpose of sequence matching. This heuristic can be turned off by settingtheautojunk argument toFalse when creating theSequenceMatcher.

在 3.2 版的變更:新增autojunk 參數。

classdifflib.Differ¶

This is a class for comparing sequences of lines of text, and producinghuman-readable differences or deltas. Differ usesSequenceMatcherboth to compare sequences of lines, and to compare sequences of characterswithin similar (near-matching) lines.

Each line of aDiffer delta begins with a two-letter code:

Code	含義
'-'	line unique to sequence 1
'+'	line unique to sequence 2
' '	line common to both sequences
'?'	line not present in either input sequence

Lines beginning with '?' attempt to guide the eye to intraline differences,and were not present in either input sequence. These lines can be confusing ifthe sequences contain whitespace characters, such as spaces, tabs or line breaks.

classdifflib.HtmlDiff¶

This class can be used to create an HTML table (or a complete HTML filecontaining the table) showing a side by side, line by line comparison of textwith inter-line and intra-line change highlights. The table can be generated ineither full or contextual difference mode.

The constructor for this class is:

__init__(tabsize=8,wrapcolumn=None,linejunk=None,charjunk=IS_CHARACTER_JUNK)¶

Initializes instance ofHtmlDiff.

tabsize is an optional keyword argument to specify tab stop spacing anddefaults to8.

wrapcolumn is an optional keyword to specify column number where lines arebroken and wrapped, defaults toNone where lines are not wrapped.

linejunk andcharjunk are optional keyword arguments passed intondiff()(used byHtmlDiff to generate the side by side HTML differences). Seendiff() documentation for argument default values and descriptions.

The following methods are public:

make_file(fromlines,tolines,fromdesc='',todesc='',context=False,numlines=5,*,charset='utf-8')¶

Comparesfromlines andtolines (lists of strings) and returns a string whichis a complete HTML file containing a table showing line by line differences withinter-line and intra-line changes highlighted.

fromdesc andtodesc are optional keyword arguments to specify from/to filecolumn header strings (both default to an empty string).

context andnumlines are both optional keyword arguments. Setcontext toTrue when contextual differences are to be shown, else the default isFalse to show the full files.numlines defaults to5. WhencontextisTruenumlines controls the number of context lines which surround thedifference highlights. Whencontext isFalsenumlines controls thenumber of lines which are shown before a difference highlight when using the"next" hyperlinks (setting to zero would cause the "next" hyperlinks to placethe next difference highlight at the top of the browser without any leadingcontext).

備註

fromdesc andtodesc are interpreted as unescaped HTML and should beproperly escaped while receiving input from untrusted sources.

在 3.5 版的變更:charset keyword-only argument was added. The default charset ofHTML document changed from'ISO-8859-1' to'utf-8'.

make_table(fromlines,tolines,fromdesc='',todesc='',context=False,numlines=5)¶

Comparesfromlines andtolines (lists of strings) and returns a string whichis a complete HTML table showing line by line differences with inter-line andintra-line changes highlighted.

The arguments for this method are the same as those for themake_file()method.

difflib.context_diff(a,b,fromfile='',tofile='',fromfiledate='',tofiledate='',n=3,lineterm='\n')¶

Comparea andb (lists of strings); return a delta (ageneratorgenerating the delta lines) in context diff format.

Context diffs are a compact way of showing just the lines that have changed plusa few lines of context. The changes are shown in a before/after style. Thenumber of context lines is set byn which defaults to three.

By default, the diff control lines (those with*** or---) are createdwith a trailing newline. This is helpful so that inputs created fromio.IOBase.readlines() result in diffs that are suitable for use withio.IOBase.writelines() since both the inputs and outputs have trailingnewlines.

For inputs that do not have trailing newlines, set thelineterm argument to"" so that the output will be uniformly newline free.

The context diff format normally has a header for filenames and modificationtimes. Any or all of these may be specified using strings forfromfile,tofile,fromfiledate, andtofiledate. The modification times are normallyexpressed in the ISO 8601 format. If not specified, thestrings default to blanks.

>>>importsys>>>fromdifflibimport*>>>s1=['bacon\n','eggs\n','ham\n','guido\n']>>>s2=['python\n','eggy\n','hamster\n','guido\n']>>>sys.stdout.writelines(context_diff(s1,s2,fromfile='before.py',...tofile='after.py'))*** before.py--- after.py****************** 1,4 ****! bacon! eggs! ham  guido--- 1,4 ----! python! eggy! hamster  guido

一個更詳盡的範例請見A command-line interface to difflib。

difflib.get_close_matches(word,possibilities,n=3,cutoff=0.6)¶

Return a list of the best "good enough" matches.word is a sequence for whichclose matches are desired (typically a string), andpossibilities is a list ofsequences against which to matchword (typically a list of strings).

Optional argumentn (default3) is the maximum number of close matches toreturn;n must be greater than0.

Optional argumentcutoff (default0.6) is a float in the range [0, 1].Possibilities that don't score at least that similar toword are ignored.

The best (no more thann) matches among the possibilities are returned in alist, sorted by similarity score, most similar first.

>>>get_close_matches('appel',['ape','apple','peach','puppy'])['apple', 'ape']>>>importkeyword>>>get_close_matches('wheel',keyword.kwlist)['while']>>>get_close_matches('pineapple',keyword.kwlist)[]>>>get_close_matches('accept',keyword.kwlist)['except']

difflib.ndiff(a,b,linejunk=None,charjunk=IS_CHARACTER_JUNK)¶

Comparea andb (lists of strings); return aDiffer-styledelta (agenerator generating the delta lines).

Optional keyword parameterslinejunk andcharjunk are filtering functions(orNone):

linejunk: A function that accepts a single string argument, and returnstrue if the string is junk, or false if not. The default isNone. Thereis also a module-level functionIS_LINE_JUNK(), which filters out lineswithout visible characters, except for at most one pound character ('#')-- however the underlyingSequenceMatcher class does a dynamicanalysis of which lines are so frequent as to constitute noise, and thisusually works better than using this function.

charjunk: A function that accepts a character (a string of length 1), andreturns if the character is junk, or false if not. The default is module-levelfunctionIS_CHARACTER_JUNK(), which filters out whitespace characters (ablank or tab; it's a bad idea to include newline in this!).

>>>diff=ndiff('one\ntwo\nthree\n'.splitlines(keepends=True),...'ore\ntree\nemu\n'.splitlines(keepends=True))>>>print(''.join(diff),end="")- one?  ^+ ore?  ^- two- three?  -+ tree+ emu

difflib.restore(sequence,which)¶

Return one of the two sequences that generated a delta.

Given asequence produced byDiffer.compare() orndiff(), extractlines originating from file 1 or 2 (parameterwhich), stripping off lineprefixes.

範例：

>>>diff=ndiff('one\ntwo\nthree\n'.splitlines(keepends=True),...'ore\ntree\nemu\n'.splitlines(keepends=True))>>>diff=list(diff)# materialize the generated delta into a list>>>print(''.join(restore(diff,1)),end="")onetwothree>>>print(''.join(restore(diff,2)),end="")oretreeemu

difflib.unified_diff(a,b,fromfile='',tofile='',fromfiledate='',tofiledate='',n=3,lineterm='\n')¶

Comparea andb (lists of strings); return a delta (ageneratorgenerating the delta lines) in unified diff format.

Unified diffs are a compact way of showing just the lines that have changed plusa few lines of context. The changes are shown in an inline style (instead ofseparate before/after blocks). The number of context lines is set byn whichdefaults to three.

By default, the diff control lines (those with---,+++, or@@) arecreated with a trailing newline. This is helpful so that inputs created fromio.IOBase.readlines() result in diffs that are suitable for use withio.IOBase.writelines() since both the inputs and outputs have trailingnewlines.

For inputs that do not have trailing newlines, set thelineterm argument to"" so that the output will be uniformly newline free.

The unified diff format normally has a header for filenames and modificationtimes. Any or all of these may be specified using strings forfromfile,tofile,fromfiledate, andtofiledate. The modification times are normallyexpressed in the ISO 8601 format. If not specified, thestrings default to blanks.

>>>s1=['bacon\n','eggs\n','ham\n','guido\n']>>>s2=['python\n','eggy\n','hamster\n','guido\n']>>>sys.stdout.writelines(unified_diff(s1,s2,fromfile='before.py',tofile='after.py'))--- before.py+++ after.py@@ -1,4 +1,4 @@-bacon-eggs-ham+python+eggy+hamster guido

一個更詳盡的範例請見A command-line interface to difflib。

difflib.diff_bytes(dfunc,a,b,fromfile=b'',tofile=b'',fromfiledate=b'',tofiledate=b'',n=3,lineterm=b'\n')¶

Comparea andb (lists of bytes objects) usingdfunc; yield asequence of delta lines (also bytes) in the format returned bydfunc.dfunc must be a callable, typically eitherunified_diff() orcontext_diff().

Allows you to compare data with unknown or inconsistent encoding. Allinputs exceptn must be bytes objects, not str. Works by losslesslyconverting all inputs (exceptn) to str, and callingdfunc(a,b,fromfile,tofile,fromfiledate,tofiledate,n,lineterm). The output ofdfunc is then converted back to bytes, so the delta lines that youreceive have the same unknown/inconsistent encodings asa andb.

在 3.5 版被加入.

difflib.IS_LINE_JUNK(line)¶

ReturnTrue for ignorable lines. The lineline is ignorable ifline isblank or contains a single'#', otherwise it is not ignorable. Used as adefault for parameterlinejunk inndiff() in older versions.

difflib.IS_CHARACTER_JUNK(ch)¶

ReturnTrue for ignorable characters. The characterch is ignorable ifchis a space or tab, otherwise it is not ignorable. Used as a default forparametercharjunk inndiff().

>>>s=SequenceMatcher(None,"abcd","bcde")>>>s.ratio()0.75>>>s.quick_ratio()0.75>>>s.real_quick_ratio()1.0

>>>s=SequenceMatcher(lambdax:x==" ",..."private Thread currentThread;",..."private volatile Thread currentThread;")

>>>print(round(s.ratio(),3))0.866

>>>forblockins.get_matching_blocks():...print("a[%d] and b[%d] match for%d elements"%block)a[0] and b[0] match for 8 elementsa[8] and b[17] match for 21 elementsa[29] and b[38] match for 0 elements

>>>foropcodeins.get_opcodes():...print("%6s a[%d:%d] b[%d:%d]"%opcode) equal a[0:8] b[0:8]insert a[8:8] b[8:17] equal a[8:29] b[17:38]

>>>text1='''  1. Beautiful is better than ugly....  2. Explicit is better than implicit....  3. Simple is better than complex....  4. Complex is better than complicated....'''.splitlines(keepends=True)>>>len(text1)4>>>text1[0][-1]'\n'>>>text2='''  1. Beautiful is better than ugly....  3.   Simple is better than complex....  4. Complicated is better than complex....  5. Flat is better than nested....'''.splitlines(keepends=True)

>>>d=Differ()

>>>result=list(d.compare(text1,text2))

>>>frompprintimportpprint>>>pprint(result)['    1. Beautiful is better than ugly.\n', '-   2. Explicit is better than implicit.\n', '-   3. Simple is better than complex.\n', '+   3.   Simple is better than complex.\n', '?     ++\n', '-   4. Complex is better than complicated.\n', '?            ^                     ---- ^\n', '+   4. Complicated is better than complex.\n', '?           ++++ ^                      ^\n', '+   5. Flat is better than nested.\n']

>>>importsys>>>sys.stdout.writelines(result)    1. Beautiful is better than ugly.-   2. Explicit is better than implicit.-   3. Simple is better than complex.+   3.   Simple is better than complex.?     ++-   4. Complex is better than complicated.?            ^                     ---- ^+   4. Complicated is better than complex.?           ++++ ^                      ^+   5. Flat is better than nested.

""" Command line interface to difflib.py providing diffs in four formats:* ndiff:    lists every line and highlights interline changes.* context:  highlights clusters of changes in a before/after format.* unified:  highlights clusters of changes in an inline format.* html:     generates side by side comparison with change highlights."""importsys,os,difflib,argparsefromdatetimeimportdatetime,timezonedeffile_mtime(path):t=datetime.fromtimestamp(os.stat(path).st_mtime,timezone.utc)returnt.astimezone().isoformat()defmain():parser=argparse.ArgumentParser()parser.add_argument('-c',action='store_true',default=False,help='Produce a context format diff (default)')parser.add_argument('-u',action='store_true',default=False,help='Produce a unified format diff')parser.add_argument('-m',action='store_true',default=False,help='Produce HTML side by side diff ''(can use -c and -l in conjunction)')parser.add_argument('-n',action='store_true',default=False,help='Produce a ndiff format diff')parser.add_argument('-l','--lines',type=int,default=3,help='Set number of context lines (default 3)')parser.add_argument('fromfile')parser.add_argument('tofile')options=parser.parse_args()n=options.linesfromfile=options.fromfiletofile=options.tofilefromdate=file_mtime(fromfile)todate=file_mtime(tofile)withopen(fromfile)asff:fromlines=ff.readlines()withopen(tofile)astf:tolines=tf.readlines()ifoptions.u:diff=difflib.unified_diff(fromlines,tolines,fromfile,tofile,fromdate,todate,n=n)elifoptions.n:diff=difflib.ndiff(fromlines,tolines)elifoptions.m:diff=difflib.HtmlDiff().make_file(fromlines,tolines,fromfile,tofile,context=options.c,numlines=n)else:diff=difflib.context_diff(fromlines,tolines,fromfile,tofile,fromdate,todate,n=n)sys.stdout.writelines(diff)if__name__=='__main__':main()

"""ndiff [-q] file1 file2    orndiff (-r1 | -r2) < ndiff_output > file1_or_file2Print a human-friendly file difference report to stdout.  Both inter-and intra-line differences are noted.  In the second form, recreate file1(-r1) or file2 (-r2) on stdout, from an ndiff report on stdin.In the first form, if -q ("quiet") is not specified, the first two linesof output are-: file1+: file2Each remaining line begins with a two-letter code:    "- "    line unique to file1    "+ "    line unique to file2    "  "    line common to both files    "? "    line not present in either input fileLines beginning with "? " attempt to guide the eye to intralinedifferences, and were not present in either input file.  These lines can beconfusing if the source files contain tab characters.The first file can be recovered by retaining only lines that begin with"  " or "- ", and deleting those 2-character prefixes; use ndiff with -r1.The second file can be recovered similarly, but by retaining only "  " and"+ " lines; use ndiff with -r2; or, on Unix, the second file can berecovered by piping the output through    sed -n '/^[+ ] /s/^..//p'"""__version__=1,7,0importdifflib,sysdeffail(msg):out=sys.stderr.writeout(msg+"\n\n")out(__doc__)return0# open a file & return the file object; gripe and return 0 if it# couldn't be openeddeffopen(fname):try:returnopen(fname)exceptIOErrorasdetail:returnfail("couldn't open "+fname+": "+str(detail))# open two files & spray the diff to stdout; return false iff a problemdeffcompare(f1name,f2name):f1=fopen(f1name)f2=fopen(f2name)ifnotf1ornotf2:return0a=f1.readlines();f1.close()b=f2.readlines();f2.close()forlineindifflib.ndiff(a,b):print(line,end=' ')return1# crack args (sys.argv[1:] is normal) & compare;# return false iff a problemdefmain(args):importgetopttry:opts,args=getopt.getopt(args,"qr:")exceptgetopt.errorasdetail:returnfail(str(detail))noisy=1qseen=rseen=0foropt,valinopts:ifopt=="-q":qseen=1noisy=0elifopt=="-r":rseen=1whichfile=valifqseenandrseen:returnfail("can't specify both -q and -r")ifrseen:ifargs:returnfail("no args allowed with -r option")ifwhichfilein("1","2"):restore(whichfile)return1returnfail("-r value must be 1 or 2")iflen(args)!=2:returnfail("need 2 filename args")f1name,f2name=argsifnoisy:print('-:',f1name)print('+:',f2name)returnfcompare(f1name,f2name)# read ndiff output from stdin, and print file1 (which=='1') or# file2 (which=='2') to stdoutdefrestore(which):restored=difflib.restore(sys.stdin.readlines(),which)sys.stdout.writelines(restored)if__name__=='__main__':main(sys.argv[1:])