Use of Regular Expressions in python, python Regular Expressions

Use of Regular Expressions in python, python Regular Expressions

This article describes the symbols and methods of python regular expressions.

Findall: searches for all matches and returns the list of all combinations.
Search: searches for the first match and returns
Sub: Replace the regular content and return the replaced content.
.: Match any character except line breaks

a = 'xy123'b = re.findall('x...',a)print(b)# ['xy12']

*: Match the first character 0 times or unlimited times

a = 'xyxy123'b = re.findall('x*',a)print(b)# ['x', '', 'x', '', '', '', '', '']

? : Match the first character 0 times or 1 time

a = 'xy123'b = re.findall('x?',a)print(b)# ['x', '', '', '', '', '']

. *: Greedy algorithm

b = re.findall('xx.*xx',secret_code)print(b)# ['xxIxxfasdjifja134xxlovexx23345sdfxxyouxx']

.*? : Non-Greedy Algorithm

c = re.findall('xx.*?xx',secret_code)print(c)# ['xxIxx', 'xxlovexx', 'xxyouxx']

(): Returns results in parentheses.

d = re.findall('xx(.*?)xx',secret_code)print(d)for each in d:  print(each)# ['I', 'love', 'you']# I# love# you

Re. S makes the. Scope include the line break "\ n"

s = '''sdfxxhelloxxfsdfxxworldxxasdf'''d = re.findall('xx(.*?)xx',s,re.S)print(d)# ['hello\n', 'world']

Comparison between findall and search

s2 = 'asdfxxIxx123xxlovexxdfd'f = re.search('xx(.*?)xx123xx(.*?)xx',s2).group(2)print(f)f2 = re.findall('xx(.*?)xx123xx(.*?)xx',s2)print(f2[0][1])# love# love

Although the results are the same, search matches the group to obtain the second match, and findall Returns [('I', 'love')], containing the list of tuples, therefore, f2 [0] [1] is required.

Use of sub

s = '123rrrrr123'output = re.sub('123(.*?)123','123%d123'%789,s)print(output)# 123789123

For example, we need to change the path of all png images in the document, that is, we need to find the end of all. png images and add them to the path,

import redef multiply(m):  # Convert group 0 to an integer.  v = m.group(0)  print(v)  # Multiply integer by 2.  # ... Convert back into string and return it.  print('basic/'+v)  return 'basic/'+v

The result is as follows:

>>>autoencoder.png  basic/autoencoder.png  RNN.png  basic/RNN.png  rnn_step_forward.png  basic/rnn_step_forward.png  rnns.png  basic/rnns.png  rnn_cell_backprop.png  basic/rnn_cell_backprop.png  LSTM.png  basic/LSTM.png  LSTM_rnn.png  basic/LSTM_rnn.png  attn_mechanism.png  basic/attn_mechanism.png  attn_model.png  basic/attn_model.png

Following the examples above, we can easily customize our tasks.

Compared with sub, subn returns a tuples. The second element indicates the number of times that a replacement occurs:

import redef add(m):  # Convert.  v = int(m.group(0))  # Add 2.  return str(v + 1)# Call re.subn.result = re.subn("\d+", add, "1 2 3 4 5")print("Result string:", result[0])print("Number of substitutions:", result[1])>>>Result string: 11 21 31 41 51Number of substitutions: 5