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 difflib 两种常用的功能：字符串比较和文本比较。
二、正文
1. 字符串比较
1.1 计算原理
相似度 = 2.0*M / T （M表示两个字符串能够匹配到的字符数量， T表示字符总数）
1.2 参数介绍
SequenceMatcher(lambda x: x in "要去除的字符", "字符串1", "字符串2")
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_time}s")
print(f'内存占用：{final_memory-initial_memory:.2f}MB')
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
以文本格式显示结果
- 示例代码
import difflib
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
以html方式显示结果
- 示例代码
import difflib
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
2.4 context_diff
返回一个差异文本行的生成器， 用颜色高亮显示文本的增加，删除或者更改
- 实例代码
from difflib import context_diff
import sys
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
*** before.py
--- after.py
***************
*** 1,4 ****
! bacon
! eggs
! ham
guido
--- 1,4 ----
! python
! eggy
! hamster
guido
2.5 get_close_matches
返回最大匹配结果的列表
- 示例代码
from difflib import get_close_matches
d=get_close_matches('appel', ['ape', 'apple', 'peach', 'puppy'])
print(d)
- 结果展示
['apple', 'ape']
2.6 ndiff
返回一个文本格式的差异结果
- 示例代码
from difflib import ndiff
diff = ndiff('one\ntwo\nthree\n'.splitlines(1),
'ore\ntree\nemu\n'.splitlines(1))
print(''.join(diff))
- 结果展示
- one
? ^
+ ore
? ^
- two
- three
? -
+ tree
+ emu
2.7 restore
返回一个由两个比对序列产生的结果
- 示例代码
from difflib import ndiff, 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
one
two
three
