如何理解`pat = r'/([^/]+)_\d+.jpg'`?

Notes from @PoonamV on forum

Regular expressions

we can use a regular expression by importing regular expression ‘re’ package in python, to do this. Regular expressions are a way to search a string in text using pattern matching methods.

pat = r'/([^/]+)_\d+.jpg

Let’s deconstruct this regex pattern, /([^/]+)_\d+.jpg$ by reading it backward:

Expression	Explanation
`$`	end of search
`.jpg`	last chars to be found in the search string, also right file format checking
`\d`	numerical digits, ‘+’ sign denotes can be one or more of them
`_`	should come before the start of digits
`()`	denotes a group of characters
`[]`	denotes another subgroup if characters in the previous group
`^/`	‘^’ denotes negation, so ‘+’ says all other chars except ‘/’
`( [ ^/ ] + )`	searches all characters except ‘/’
`/`	first ‘/’ in regex says, end of search
`r`	The string should be a raw string. Otherwise, `\d` would have to be written as `\\d` so that Python doesn’t interpret it to be a special character.

So, this regex pattern will give us a string

Abyssinian_1.jpg

considering search string was

PosixPath('images/Abyssinian_1.jpg')

Further, by using the fact that the actual name of the breed is in the first parenthesized group of the regular expression, the actual breed name

Abyssinian

can be obtained by using ‘.group(1)’ wherever the search on the regular expression is performed.See this for details.

credits @dreambeats

See this blog post to understand this regular expression in detail. The python documentation has a tutorial on regular expressions. RegexOne provides a simple interactive intro to regular expressions.

EmbraceLife / shendusuipian

如何理解`pat = r'/([^/]+)_\d+.jpg'`? #62

Regular expressions

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