Python爬虫常用的正则表达式学习

╰+哭是因爲堅強的太久メ 2022-04-22 03:38 183阅读 0赞

## *Python通过re模块提供对正则表达式的支持。* ##

import re

# #

## *字符串匹配* ##

# matching string
    p1 = "cat"
    p2 = "dog"
    string = "dog runs to bird"
    print (p1 in string)  # True
    print (p2 in string)  # False

## *正则寻找配对* ##

# regular expression
    p1 = "cat"
    p2 = "bird"
    string = "dog runs to cat"
    print(re.search(p1, string))  # <_sre.SRE_Match object; span=(12, 15), match='cat'>
    print(re.search(p2, string))  # None

## *匹配多种可能  使用\[\]* ##

# multiple patterns ("run" or "ran")
    ptn = r"r[au]n"       # start with "r" means raw string
    print(re.search(ptn, "dog runs to cat"))    # <_sre.SRE_Match object; span=(4, 7), match='run'>

## *匹配更多种可能* ##

# continue
    print(re.search(r"r[A-Z]n", "dog runs to cat"))     # None
    print(re.search(r"r[a-z]n", "dog runs to cat"))     # <_sre.SRE_Match object; span=(4, 7), match='run'>
    print(re.search(r"r[0-9]n", "dog r2ns to cat"))     # <_sre.SRE_Match object; span=(4, 7), match='r2n'>
    print(re.search(r"r[0-9a-z]n", "dog runs to cat"))  # <_sre.SRE_Match object; span=(4, 7), match='run'>

## *特殊种类匹配* ##

### ***数字*** ###

# \d : decimal digit
    print(re.search(r"r\dn", "run r4n"))                # <_sre.SRE_Match object; span=(4, 7), match='r4n'>
    # \D : any non-decimal digit
    print(re.search(r"r\Dn", "run r4n"))                # <_sre.SRE_Match object; span=(0, 3), match='run'>

### *空格* ###

# \s : any white space [\t\n\r\f\v]
    print(re.search(r"r\sn", "r\nn r4n"))               # <_sre.SRE_Match object; span=(0, 3), match='r\nn'>
    # \S : opposite to \s, any non-white space
    print(re.search(r"r\Sn", "r\nn r4n"))               # <_sre.SRE_Match object; span=(4, 7), match='r4n'>

### *所有字母数字和"\_"* ###

# \w : [a-zA-Z0-9_]
    print(re.search(r"r\wn", "r\nn r4n"))               # <_sre.SRE_Match object; span=(4, 7), match='r4n'>
    # \W : opposite to \w
    print(re.search(r"r\Wn", "r\nn r4n"))               # <_sre.SRE_Match object; span=(0, 3), match='r\nn'>

### *空白字符* ###

# \b : empty string (only at the start or end of the word)
    print(re.search(r"\bruns\b", "dog runs to cat"))    # <_sre.SRE_Match object; span=(4, 8), match='runs'>
    # \B : empty string (but not at the start or end of a word)
    print(re.search(r"\B runs \B", "dog   runs  to cat"))  # <_sre.SRE_Match object; span=(8, 14), match=' runs '>

### *特殊字符（反斜杠）* ###

# \\ : match \
    print(re.search(r"runs\\", "runs\ to me"))          # <_sre.SRE_Match object; span=(0, 5), match='runs\\'>
    # . : match anything (except \n)
    print(re.search(r"r.n", "r[ns to me"))              # <_sre.SRE_Match object; span=(0, 3), match='r[n'>

### *句首句尾* ###

# ^ : match line beginning
    print(re.search(r"^dog", "dog runs to cat"))        # <_sre.SRE_Match object; span=(0, 3), match='dog'>
    # $ : match line ending
    print(re.search(r"cat$", "dog runs to cat"))        # <_sre.SRE_Match object; span=(12, 15), match='cat'>

### *是否* ###

# ? : may or may not occur
    print(re.search(r"Mon(day)?", "Monday"))            # <_sre.SRE_Match object; span=(0, 6), match='Monday'>
    print(re.search(r"Mon(day)?", "Mon"))               # <_sre.SRE_Match object; span=(0, 3), match='Mon'>

### *多行匹配* ###

# multi-line
    string = """
    dog runs to cat.
    I run to dog.
    """
    print(re.search(r"^I", string))                     # None
    print(re.search(r"^I", string, flags=re.M))         # <_sre.SRE_Match object; span=(18, 19), match='I'>
                                           #M表示multiline

### *0或多次* ###

# * : occur 0 or more times
    print(re.search(r"ab*", "a"))                       # <_sre.SRE_Match object; span=(0, 1), match='a'>
    print(re.search(r"ab*", "abbbbb"))                  # <_sre.SRE_Match object; span=(0, 6), match='abbbbb'>

### *1或多次* ###

# + : occur 1 or more times
    print(re.search(r"ab+", "a"))                       # None
    print(re.search(r"ab+", "abbbbb"))                  # <_sre.SRE_Match object; span=(0, 6), match='abbbbb'>

### *可选次数* ###

# {n, m} : occur n to m times
    print(re.search(r"ab{2,10}", "a"))                  # None
    print(re.search(r"ab{2,10}", "abbbbb"))             # <_sre.SRE_Match object; span=(0, 6), match='abbbbb'>

### *group组* ###

match = re.search(r"(\d+), Date: (.+)", "ID: 021523, Date: Feb/12/2017")
    print(match.group())                                # 021523, Date: Feb/12/2017
    print(match.group(1))                               # 021523
    print(match.group(2))                               # Date: Feb/12/2017
    
    match = re.search(r"(?P<id>\d+), Date: (?P<date>.+)", "ID: 021523, Date: Feb/12/2017")
    print(match.group('id'))                            # 021523
    print(match.group('date'))                          # Date: Feb/12/2017

## *找到全部匹配* ##

# findall
    print(re.findall(r"r[ua]n", "run ran ren"))         # ['run', 'ran']
    # | : or
    print(re.findall(r"(run|ran)", "run ran ren"))      # ['run', 'ran']

## *替换* ##

# re.sub() replace
    print(re.sub(r"r[au]ns", "catches", "dog runs to cat"))     # dog catches to cat

## *分裂* ##

# re.split()
    print(re.split(r"[,;\.]", "a;b,c.d;e"))             # ['a', 'b', 'c', 'd', 'e']

## *compile* ##

# compiled_re = re.compile(r"r[ua]n")
    print(compiled_re.search("dog ran to cat")) # <_sre.SRE_Match object; span=(4, 7), match='ran'>

以上来源于学习视频：[https://www.youtube.com/watch?v=l1MAW1z641E][https_www.youtube.com_watch_v_l1MAW1z641E]

[https_www.youtube.com_watch_v_l1MAW1z641E]: https://www.youtube.com/watch?v=l1MAW1z641E