python difflib文本比较利器，入手不亏

Posted 2022-08-22 Coderusher

@[toc]

一、引言

difflib模块：是提供的类和方法用来进行序列的差异化比较，它能够比对文件并生成差异结果文本或者html格式的差异化比较页面。其作为 python 的内置库，有着强大的文本比对功能，此篇介绍五个常用的 difflib 功能

二、正文

1. 字符串比较

1.1 计算原理

1.2 参数介绍

1.3 举个栗子

• 实例1

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

  如果想要去除掉多余的字符再进行比较

• 实例2

  >>> s = SequenceMatcher(lambda x: x in "|\\", "abcd|", "dc\\fa") # 去除两个字符中的 ( | ) 以及 ( \\ ) 符号后比较
  >>> s.ratio()
  0.75
  >>> s.quick_ratio()
  0.75

1.4 相关函数性能比较

函数	计算速度	内存开销
ratio()	快	大
quick_ratio()	慢	小

• 论证过程
  将相似度比对过程遍历100000遍得到计算速度与内存占用上的差异

# 导入第三方库
import os
import psutil
import time

def show_info():
    pid = os.getpid()
    #模块名比较容易理解：获得当前进程的pid
    p = psutil.Process(pid)
    #根据pid找到进程，进而找到占用的内存值
    info = p.memory_full_info()
    memory = info.uss/1024/1024
    return memory

def func(ratio_func):
    start_time = time.time() # 记录起始时间
    initial_memory = show_info()  # 记录起始内存
    if ratio_func == "ratio":
        ratio = [similarity.ratio() for i in range(1000000)]
    else:
        ratio = [similarity.quick_ratio() for i in range(1000000)]
    final_memory = show_info()  # 记录终止内存
    end_time = time.time()  # 记录终止时间
    print(f"耗时：end_time-start_times")
    print(f内存占用：final_memory-initial_memory:.2fMB)

if __name__ == __main__:
    similarity = difflib.SequenceMatcher(None, 需要比对的字符1, 需要比对的字符2)
    func("ratio")
    func("quick_ratio")

• 输出结果

  >>> func("ratio")
  耗时：0.9709699153900146s
  内存占用：36.58MB
  >>> func("quick_ratio")
  耗时：2.730135917663574s
  内存占用：32.68MB

2. 文本比较

2.1 相关符号与含义

符号	含义
-	仅在片段1中存在
+	仅在片段2中存在
(空格)	片段1和2中都存在
?	下标显示
^	存在差异字符

2.2 Differ

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)

text2 =

1. Beautifu 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)

#以文本方式展示两个文本的不同:
d = difflib.Differ()
result = list(d.compare(text1, text2))
result = " ".join(result)
print(result)

- 结果展示

• 1. Beautiful is better than ugly.
     ? ^
• 1. Beautifu is better than ugly.
     ? ^
     2. Explicit is better than implicit.
     3. Simple is better than complex.
     4. Complex is better than complicated.

2.3 HtmlDiff

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)

text2 =

1. Beautifu 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)
   #以html方式展示两个文本的不同， 浏览器打开:
   d = difflib.HtmlDiff()
   with open("passwd.html", w) as f:
   f.write(d.make_file(text1, text2))

   
   - 结果展示
   ![image.png](https://s2.51cto.com/images/20220819/1660911791958174.png?x-oss-process=image/watermark,size_14,text_QDUxQ1RP5Y2a5a6i,color_FFFFFF,t_30,g_se,x_10,y_10,shadow_20,type_ZmFuZ3poZW5naGVpdGk=)

2.4 context_diff

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)

对于字符串列表进行比较，可以看出只有第四个元素是相同的,每个元素会依次进行比较，而不是按照索引进行比较，假使s1 = [eggs\\n, ham\\n, guido\\n]为三个元素

- 结果展示
```python
*** before.py
--- after.py
***************
*** 1,4 ****
! bacon
! eggs
! ham
  guido
--- 1,4 ----
! python
! eggy
! hamster
  guido

2.5 get_close_matches

d=get_close_matches(appel, [ape, apple, peach, puppy])
print(d)

- 结果展示
```python
[apple, ape]

2.6 ndiff

diff = ndiff(one\\ntwo\\nthree\\n.splitlines(1),
ore\\ntree\\nemu\\n.splitlines(1))
print(.join(diff))

- 结果展示
```python
- one
?  ^
+ ore
?  ^
- two
- three
?  -
+ tree
+ emu

2.7 restore

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)))

- 结果展示
```python
one
two
three

3. 参考链接

python中difflib模块祥解