What does this regex mean in python? [duplicate]

问题:

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I am new to Python and I am trying to understand this regex:

pattern = r"^[A-Z0-9._%+-]+@[A-Z0-9.-]{2,200}$" 

What does %+- and .- mean?

回答1:

[%+-] means match either %, +, or -. Why we don't use escape character \ ? because they are in side []

[.-] means match either . or - Why we don't use escape character \ ? because they are in side [],

Furthermore - can also mean a range if between a range characters like [A-Z] or [0-9] in other case it is treated literally as in [AZ-].

回答2:

They're inside [], so they're part of a character class. It matches those literal characters.

A - is a special character inside a character class only if it appears somewhere in the middle of the class (as in A-Z, where it means the whole range of characters from A to Z). If it appears at the beginning or end of the class, it means a literal -.

(That regular expression looks like it matches an email address, for a certain definition of "email address.")

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