Detailed explanation of python difflib module

This article mainly introduces examples of the python difflib module in detail, which has certain reference value. Interested friends can refer to the classes and methods provided by the

difflib module for sequencing. Differential comparison, it can compare files and generate differential result text or differential comparison page in html format. If you need to compare directories, you can use the filecmp module.

class difflib.SequenceMatcher

This class provides methods for comparing sequence pairs of arbitrary hashable types. This method will find the largest consecutive matching sequence that does not contain 'garbage' elements.

By comparing the complexity of the algorithm, it has n square operations in the worst case due to the original Gestalt matching algorithm, and has linear efficiency in the best case.

It has automatic garbage heuristics that can treat characters that are repeated more than 1% of the fragment or repeated 200 times as garbage. This feature can be turned off by setting autojunk to false.

class difflib.Differ

This class compares the differences between text lines and produces difference results or incremental results suitable for human reading. Each of the results The representation of the parts is as follows:

##class difflib.HtmlDiff

This class can be used to create HTML tables (or contain tables html file), corresponding display on both sides or row-by-row display to compare the difference results.

make_file(fromlines, tolines [, fromdesc][, todesc][, context][, numlines])

make_table(fromlines, tolines [, fromdesc][, todesc][, context ][, numlines])

Both of the above two methods can be used to generate an html file containing a table containing the comparison results, and part of the content will be highlighted.

difflib.context_diff(a, b[, fromfile][, tofile][, fromfiledate][, tofiledate][, n][, lineterm])

Generator that compares a and b (a list of strings) and returns a line of difference text

Example:

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

difflib.get_close_matches(word, possibilities [, n][, cutoff])

Return the list of maximum matching results

Example:

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

difflib.ndiff(a, b[, linejunk][, charjunk])

Compare a and b (string list) and return a Differ-style difference result

Example:

>>> diff = ndiff('one\ntwo\nthree\n'.splitlines(1),
...       'ore\ntree\nemu\n'.splitlines(1))
>>> print ''.join(diff),
- one
? ^
+ ore
? ^
- two
- three
? -
+ tree
+ emu

difflib.restore(sequence, which)

Returns a result produced by two aligned sequences

Example

>>> diff = ndiff('one\ntwo\nthree\n'.splitlines(1),
...       'ore\ntree\nemu\n'.splitlines(1))
>>> diff = list(diff) # materialize the generated delta into a list
>>> print ''.join(restore(diff, 1)),
one
two
three
>>> print ''.join(restore(diff, 2)),
ore
tree
emu

difflib.unified_diff(a, b[, fromfile][, tofile][, fromfiledate][, tofiledate ][, n][, lineterm])

Compare a and b (string list) and return a difference result in unified diff format.

Example:

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

Practical application example

Compare two files and then generate an HTML file showing the difference results

#coding:utf-8
'''
file:difflibeg.py
date:2017/9/9 10:33
author:lockey
email:lockey@123.com
desc:diffle module learning and practising 
'''
import difflib
hd = difflib.HtmlDiff()
loads = ''
with open('G:/python/note/day09/0907code/hostinfo/cpu.py','r') as load:
 loads = load.readlines()
 load.close()

mems = ''
with open('G:/python/note/day09/0907code/hostinfo/mem.py', 'r') as mem:
 mems = mem.readlines()
 mem.close()

with open('htmlout.html','a+') as fo:
 fo.write(hd.make_file(loads,mems))
 fo.close()

Running results:

## Generated html file comparison results:

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