regex 或正则表达式是形成搜索模式的字符序列。
regex 可用于检查字符串是否包含指定的搜索模式。
regex 模块python 提供名为 re 的内置包，可用于处理正则表达式。
导入 re 模块：
import re
python 中的 regex导入 re 模块后，就可以开始使用正则表达式了：
实例
检索字符串以查看它是否以 “china” 开头并以 “country” 结尾：
import retxt = "china is a great country"x = re.search("^china.*country$", txt)
运行实例
import retxt = "china is a great country"x = re.search("^china.*country$", txt)if (x): print("yes! we have a match!")else: print("no match")
regex 函数re 模块提供了一组函数，允许我们检索字符串以进行匹配：
元字符元字符是具有特殊含义的字符
字符：[] 描述：一组字符 示例：“[a-m]”
import restr = "the rain in spain"#find all lower case characters alphabetically between "a" and "m":x = re.findall("[a-m]", str)print(x)
运行示例
字符： 描述：示意特殊序列（也可用于转义特殊字符） 示例：“\d”
import restr = "that will be 59 dollars"#find all digit characters:x = re.findall("\d", str)print(x)
运行示例
字符：. 描述：任何字符（换行符除外） 示例： “he…o”
import restr = "hello world"#search for a sequence that starts with "he", followed by two (any) characters, and an "o":x = re.findall("he..o", str)print(x)
运行示例
字符：^ 描述：起始于 示例： “^hello”
import restr = "hello world"#check if the string starts with 'hello':x = re.findall("^hello", str)if (x): print("yes, the string starts with 'hello'")else: print("no match")
运行示例
字符：$ 描述：结束于 示例：“world$”
import restr = "hello world"#check if the string ends with 'world':x = re.findall("world$", str)if (x): print("yes, the string ends with 'world'")else: print("no match")
运行示例
字符：* 描述：零次或多次出现 示例：“aix*”
import restr = "the rain in spain falls mainly in the plain!"#check if the string contains "ai" followed by 0 or more "x" characters:x = re.findall("aix*", str)print(x)if (x): print("yes, there is at least one match!")else: print("no match")
运行示例
字符：+ 描述：一次或多次出现 示例： “aix+”
import restr = "the rain in spain falls mainly in the plain!"#check if the string contains "ai" followed by 1 or more "x" characters:x = re.findall("aix+", str)print(x)if (x): print("yes, there is at least one match!")else: print("no match")
运行示例
字符：{} 描述： 确切地指定的出现次数 示例：“al{2}”
import restr = "the rain in spain falls mainly in the plain!"#check if the string contains "a" followed by exactly two "l" characters:x = re.findall("al{2}", str)print(x)if (x): print("yes, there is at least one match!")else: print("no match")
运行示例
字符：| 描述：两者任一 示例：“falls|stays”
import restr = "the rain in spain falls mainly in the plain!"#check if the string contains either "falls" or "stays":x = re.findall("falls|stays", str)print(x)if (x): print("yes, there is at least one match!")else: print("no match")
运行示例
字符：() 描述：捕获和分组
特殊序列特殊序列指的是 \ 后跟下表中的某个字符，拥有特殊含义。
字符：\a 描述：如果指定的字符位于字符串的开头，则返回匹配项 示例：“\athe”
import restr = "the rain in spain"#check if the string starts with "the":x = re.findall("\athe", str)print(x)if (x): print("yes, there is a match!")else: print("no match")
运行示例
字符：\b
描述：返回指定字符位于单词的开头或末尾的匹配项
示例：r"\bain"
import restr = "the rain in spain"#check if "ain" is present at the beginning of a word:x = re.findall(r"\bain", str)print(x)if (x): print("yes, there is at least one match!")else: print("no match")
运行示例
示例：r"ain\b"
import restr = "the rain in spain"#check if "ain" is present at the end of a word:x = re.findall(r"ain\b", str)print(x)if (x): print("yes, there is at least one match!")else: print("no match")
运行示例
字符：\b
描述：返回指定字符存在的匹配项，但不在单词的开头（或结尾处）
示例：r"\bain"
import restr = "the rain in spain"#check if "ain" is present, but not at the beginning of a word:x = re.findall(r"\bain", str)print(x)if (x): print("yes, there is at least one match!")else: print("no match")
运行示例
示例：r"ain\b"
import restr = "the rain in spain"#check if "ain" is present, but not at the end of a word:x = re.findall(r"ain\b", str)print(x)if (x): print("yes, there is at least one match!")else: print("no match")
运行示例
字符：\d
描述：返回字符串包含数字的匹配项（数字 0-9）
示例：“\d”
import restr = "the rain in spain"#check if the string contains any digits (numbers from 0-9):x = re.findall("\d", str)print(x)if (x): print("yes, there is at least one match!")else: print("no match")
运行示例
字符：\d
描述：返回字符串不包含数字的匹配项
示例：“\d”
import restr = "the rain in spain"#return a match at every no-digit character:x = re.findall("\d", str)print(x)if (x): print("yes, there is at least one match!")else: print("no match")
运行示例
字符：\s
描述：返回字符串包含空白字符的匹配项
示例：“\s”
import restr = "the rain in spain"#return a match at every white-space character:x = re.findall("\s", str)print(x)if (x): print("yes, there is at least one match!")else: print("no match")
运行示例
字符：\s
描述：返回字符串不包含空白字符的匹配项
示例：“\s”
import restr = "the rain in spain"#return a match at every non white-space character:x = re.findall("\s", str)print(x)if (x): print("yes, there is at least one match!")else: print("no match")
运行示例
字符：\w
描述： 返回一个匹配项，其中字符串包含任何单词字符 （从 a 到 z 的字符，从 0 到 9 的数字和下划线 _ 字符）
示例：“\w”
import restr = "the rain in spain"#return a match at every word character (characters from a to z, digits from 0-9, and the underscore _ character):x = re.findall("\w", str)print(x)if (x): print("yes, there is at least one match!")else: print("no match")
运行示例
字符：\w
描述：返回一个匹配项，其中字符串不包含任何单词字符
示例：“\w”
import restr = "the rain in spain"#return a match at every non word character (characters not between a and z. like "!", "?" white-space etc.):x = re.findall("\w", str)print(x)if (x): print("yes, there is at least one match!")else: print("no match")
运行示例
字符：\z
描述：如果指定的字符位于字符串的末尾，则返回匹配项 。
示例：“spain\z”
import restr = "the rain in spain"#check if the string ends with "spain":x = re.findall("spain\z", str)print(x)if (x): print("yes, there is a match!")else: print("no match")
运行示例
集合（set）集合（set）是一对方括号 [] 内的一组字符，具有特殊含义。
字符：[arn]
描述：返回一个匹配项，其中存在指定字符（a，r 或 n）之一
示例
import restr = "the rain in spain"#check if the string has any a, r, or n characters:x = re.findall("[arn]", str)print(x)if (x): print("yes, there is at least one match!")else: print("no match")
运行示例
字符：[a-n]
描述：返回字母顺序 a 和 n 之间的任意小写字符匹配项
示例
import restr = "the rain in spain"#check if the string has any characters between a and n:x = re.findall("[a-n]", str)print(x)if (x): print("yes, there is at least one match!")else: print("no match")
运行示例
字符：[^arn]
描述：返回除 a、r 和 n 之外的任意字符的匹配项
示例
import restr = "the rain in spain"#check if the string has other characters than a, r, or n:x = re.findall("[^arn]", str)print(x)if (x): print("yes, there is at least one match!")else: print("no match")
运行示例
字符：[0123]
描述：返回存在任何指定数字（0、1、2 或 3）的匹配项
示例
import restr = "the rain in spain"#check if the string has any 0, 1, 2, or 3 digits:x = re.findall("[0123]", str)print(x)if (x): print("yes, there is at least one match!")else: print("no match")
运行示例
字符：[0-9]
描述：返回 0 与 9 之间任意数字的匹配
示例
import restr = "8 times before 11:45 am"#check if the string has any digits:x = re.findall("[0-9]", str)print(x)if (x): print("yes, there is at least one match!")else: print("no match")
运行示例
字符：[0-5][0-9]
描述：返回介于 0 到 9 之间的任何数字的匹配项
示例
import restr = "8 times before 11:45 am"#check if the string has any two-digit numbers, from 00 to 59:x = re.findall("[0-5][0-9]", str)print(x)if (x): print("yes, there is at least one match!")else: print("no match")
运行示例
字符：[a-za-z]
描述：返回字母顺序 a 和 z 之间的任何字符的匹配，小写或大写
示例
import restr = "8 times before 11:45 am"#check if the string has any characters from a to z lower case, and a to z upper case:x = re.findall("[a-za-z]", str)print(x)if (x): print("yes, there is at least one match!")else: print("no match")
运行示例
字符：[+]
描述：在集合中，+、*、.、|、()、$、{} 没有特殊含义，因此 [+] 表示：返回字符串中任何 + 字符的匹配项。
示例
import restr = "8 times before 11:45 am"#check if the string has any + characters:x = re.findall("[+]", str)print(x)if (x): print("yes, there is at least one match!")else: print("no match")
运行示例
findall() 函数findall() 函数返回包含所有匹配项的列表。
实例
打印所有匹配的列表
import restr = "china is a great country"x = re.findall("a", str)print(x)
运行实例
这个列表以被找到的顺序包含匹配项。
如果未找到匹配项，则返回空列表。
实例
如果未找到匹配，则返回空列表：
import restr = "china is a great country"x = re.findall("usa", str)print(x)
运行实例
search() 函数search() 函数搜索字符串中的匹配项，如果存在匹配则返回 match 对象。
如果有多个匹配，则仅返回首个匹配项。
实例
在字符串中搜索第一个空白字符
import restr = "china is a great country"x = re.search("\s", str)print("the first white-space character is located in position:", x.start())
运行实例
如果未找到匹配，则返回值 none：
实例
进行不返回匹配的检索
import restr = "china is a great country"x = re.search("usa", str)print(x)
运行实例
split() 函数split() 函数返回一个列表，其中字符串在每次匹配时被拆分。
实例
在每个空白字符处进行拆分
import restr = "china is a great country"x = re.split("\s", str)print(x)
运行实例
可以通过指定 maxsplit 参数来控制出现次数：
实例
仅在首次出现时拆分字符串：
import restr = "china is a great country"x = re.split("\s", str, 1)print(x)
运行实例
sub() 函数sub() 函数把匹配替换为您选择的文本
实例
用数字 9 替换每个空白字符
import restr = "china is a great country"x = re.sub("\s", "9", str)print(x)
运行实例
可以通过指定 count 参数来控制替换次数：
实例
替换前两次出现
import restr = "china is a great country"x = re.sub("\s", "9", str, 2)print(x)
运行实例
match 对象match 对象是包含有关搜索和结果信息的对象。
注释：如果没有匹配，则返回值 none，而不是 match 对象。
实例
执行会返回 match 对象的搜索：
import restr = "china is a great country"x = re.search("a", str)print(x) # 将打印一个对象
运行实例
match 对象提供了用于取回有关搜索及结果信息的属性和方法：
span() 返回的元组包含了匹配的开始和结束位置
.string 返回传入函数的字符串
group() 返回匹配的字符串部分
实例
打印首个匹配出现的位置（开始和结束位置）。
正则表达式查找以大写 “c” 开头的任何单词：
import restr = "china is a great country"x = re.search(r"\bc\w+", str)print(x.span())
运行实例
实例
打印传入函数的字符串
import restr = "china is a great country"x = re.search(r"\bc\w+", str)print(x.string)
运行实例
实例
打印匹配的字符串部分
正则表达式查找以大写 “c” 开头的任何单词：
import restr = "china is a great country"x = re.search(r"\bc\w+", str)print(x.group())
运行实例
注释：如果没有匹配项，则返回值 none，而不是 match 对象。
以上就是python的regex正则表达式怎么使用的详细内容。