Python Difflib Deltas 和比较 Ndiff

Question

我想做一些我认为更改控制系统所做的事情，它们比较两个文件，并在每次文件更改时保存一个小的差异。我一直在阅读此页面:http://docs.python.org/library/difflib.html而且它显然没有沉入我的脑海。

我试图在下面显示的一个有点简单的程序中重新创建它，但我似乎缺少的是 Delta 包含的内容至少与原始文件一样多，甚至更多。

难道不可能只进行纯粹的更改吗？我问的原因很明显 - 节省磁盘空间。
我可以每次都保存整个代码块，但最好只保存一次当前代码，然后保存小的差异。

我还在试图弄清楚为什么许多 difflib 函数返回一个生成器而不是一个列表，这有什么好处？

difflib 对我有用吗？还是我需要找一个功能更多的更专业的软件包？

# Python Difflib demo 
# Author: Neal Walters 
# loosely based on http://ahlawat.net/wordpress/?p=371
# 01/17/2011 

# build the files here - later we will just read the files probably 
file1Contents="""
for j = 1 to 10: 
   print "ABC"
   print "DEF" 
   print "HIJ"
   print "JKL"
   print "Hello World"
   print "j=" + j 
   print "XYZ"
"""

file2Contents = """
for j = 1 to 10: 
   print "ABC"
   print "DEF" 
   print "HIJ"
   print "JKL"
   print "Hello World"
   print "XYZ"
print "The end"
"""

filename1 = "diff_file1.txt" 
filename2 = "diff_file2.txt" 

file1 = open(filename1,"w") 
file2 = open(filename2,"w") 

file1.write(file1Contents) 
file2.write(file2Contents) 

file1.close()
file2.close() 
#end of file build 

lines1 = open(filename1, "r").readlines()
lines2 = open(filename2, "r").readlines()

import difflib

print "\n FILE 1 \n" 
for line in lines1:
  print line 

print "\n FILE 2 \n" 
for line in lines2: 
  print line 

diffSequence = difflib.ndiff(lines1, lines2) 

print "\n ----- SHOW DIFF ----- \n" 
for i, line in enumerate(diffSequence):
    print line

diffObj = difflib.Differ() 
deltaSequence = diffObj.compare(lines1, lines2) 
deltaList = list(deltaSequence) 

print "\n ----- SHOW DELTALIST ----- \n" 
for i, line in enumerate(deltaList):
    print line



#let's suppose we store just the diffSequence in the database 
#then we want to take the current file (file2) and recreate the original (file1) from it
#by backward applying the diff 

restoredFile1Lines = difflib.restore(diffSequence,1)  # 1 indicates file1 of 2 used to create the diff 

restoreFileList = list(restoredFile1Lines)

print "\n ----- SHOW REBUILD OF FILE1 ----- \n" 
# this is not showing anything! 
for i, line in enumerate(restoreFileList): 
    print line

谢谢!

更新:

contextDiffSeq = difflib.context_diff(lines1, lines2) 
contextDiffList = list(contextDiffSeq) 

print "\n ----- SHOW CONTEXTDIFF ----- \n" 
for i, line in enumerate(contextDiffList):
    print line

----- SHOW CONTEXTDIFF -----

---

---

---

* 5,9 **

 print "HIJ"

 print "JKL"

 print "Hello World"

• print "j=" + j

  print "XYZ"

--- 5,9 ----

 print "HIJ"

 print "JKL"

 print "Hello World"

 print "XYZ"

• print "The end"

另一个更新:

在 Panvalet 和 Librarian 的过去，大型机的源代码管理工具，你可以像这样创建一个变更集:

++ADD 9
   print "j=" + j 

这只是意味着在第 9 行之后添加一行(或多行)。然后是像++REPLACE 或++UPDATE 这样的单词。 http://www4.hawaii.gov/dags/icsd/ppmo/Stds_Web_Pages/pdf/it110401.pdf

Answer 1

I'm also still trying to figure out why many difflib functions return a generator instead of a list, what's the advantage there?

好吧，想一想 - 如果你比较文件，这些文件在理论上(并且在实践中)会非常大 - 将增量作为列表返回，例如，意味着将完整的数据读入内存，这不是明智之举。

至于只返回差异，嗯，使用生成器还有另一个优势 - 只需迭代增量并保留您感兴趣的任何行。

如果您阅读 difflib documentation对于 Differ - style deltas，你会看到这样一段话:

Each line of a Differ delta begins with a two-letter code:
Code    Meaning
'- '    line unique to sequence 1
'+ '    line unique to sequence 2
'  '    line common to both sequences
'? '    line not present in either input sequence

因此，如果您只想要差异，可以使用 str.startswith 轻松过滤掉它们

您还可以使用 difflib.context_diff 获取仅显示更改的紧凑增量。