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正则表达式
正则表达式（有时缩写为regexp, regex, 或 re）是一种用于匹配文本模式的工具。在Python中，我们有re模块。正则表达式的应用范围很广，但它们相当复杂，因此在考虑使用正则表达式处理某个任务时，先考虑其他替代方案，最后再选择使用正则表达式。
一个正则表达式的示例是 r"^(From|To|Cc).*[email protected]" 现在解释一下：
插入符号 ^ 匹配行首的文本。接下来的组，即包含(From|To|Cc)的部分表示行必须以用管道符号|分开的词之一开头。这称为OR运算符，并且如果行以组中的任何单词开头，则正则表达式将匹配。.*?表示非贪婪地匹配除换行符\n之外的任意数量的字符。非贪婪部分意味着尽可能少地匹配重复。.字符表示任何非换行字符，*表示重复0次或多次，而?字符使其成为非贪婪。
因此，以下几行将与该正则表达式匹配：
From: [email protected]
To: !asp]<,. [email protected]
关于re语法的完整参考可在python docs找到。
关于“正确”电子邮件匹配正则表达式的示例（如练习中的），请参见此处
# Example:
import re
pattern = re.compile(r"\[(on|off)\]") # Slight optimization
print(re.search(pattern, "Mono: Playback 65 [75%] [-16.50dB] [on]"))
# Returns a Match object!
print(re.search(pattern, "Nada...:-("))
# Doesn't return anything.
# End Example
# Exercise: make a regular expression that will match an email
def test_email(your_pattern):
pattern = re.compile(your_pattern)
emails = ["[email protected]", "[email protected]", "wha.t.`1an?ug{}[email protected]"]
for email in emails:
if not re.match(pattern, email):
print("You failed to match %s" % (email))
elif not your_pattern:
print("Forgot to enter a pattern!")
else:
print("Pass")
pattern = r"" # Your pattern here!
test_email(pattern)
# Exercise: make a regular expression that will match an email
import re
def test_email(your_pattern):
pattern = re.compile(your_pattern)
emails = ["[email protected]", "[email protected]", "wha.t.`1an?ug{}[email protected]"]
for email in emails:
if not re.match(pattern, email):
print("You failed to match %s" % (email))
elif not your_pattern:
print("Forgot to enter a pattern!")
else:
print("Pass")
# Your pattern here!
pattern = r"\"?([-a-zA-Z0-9.`?{}]+@\w+\.\w+)\"?"
test_email(pattern)
test_output_contains("Pass")
success_msg("Great work!")
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