How to use regular expressions in crawlers

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1. Regular expressions: common symbols for learning regular expressions

2. Re module: learn how to use re module in python

3. Combined application of Requests and re modules: case description

Regular expression:

General characters:

Predefined characters:

Quantifier:

Boundary matching:

(?) The parentheses return the result,.? Match any character

Import re

A = 'xxIxxmexxlovexxsffaxxpythonxx'

Infos = re.findall ('xx (. *?) xx',a)

Print (infos)

Output result: Ipaw love, python

Re module and method thereof

Search () function: matches and extracts the first content that conforms to the rule, and returns a regular expression object

Re.match (pattern,string,flags=0)

Where:

(1) pattern is a matching regular expression

(2) string is the string to be matched

(3) flags is the flag bit, which is used to control the matching mode of regular expressions, such as case sensitivity, multi-line matching, etc.

Import re

Axiomane1two2three3'

Infos=re.search ('\ dflowers, a)

Print (infos)

Output:

Import re

Axiomane1two2three3'

Infos=re.search ('\ dflowers, a)

Print (infos.group ())

Output: 1

Sub () function: used to replace matches in a string

Re.sub (pattern,repl,string,count=0,flags=0)

Where:

(1) pattern is a matching regular expression

(2) repl is a replacement string

(3) string is the original string to be found and replaced

(4) counts is the maximum number of substitutions after pattern matching. Default 0 means replacing all matches.

(5) flags is the flag bit, which is used to control the matching mode of regular expressions, such as case sensitivity, multi-line matching, etc.

Import re

Phone='123-456789'

New_phone=re.sub ('\ Dawns, girls, phones, phones)

Print (new_phone)

Output: 123456789

The findall () function: matches everything that conforms to the rule and returns the result as a list.

Import re

Axiomane1two2three3'

Infos2=re.findall ('\ dflowers, a)

Print (infos2)

Output: ['1','2','3']

Import re

A =''index

''

Word = re.findall ('(. *?)', a, re.S)

Print (word [0] .strip ())

Output: index

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