re (정규표현식 작업 모듈)

00 개요

코드분석 시 나오길래 정리하고자 함
re는 regular expression(정규 표현식)의 약자인데 뭔지 알고자 할 경우 다음을 참조 (2024.03.26 - [Python/기본문법] - Regular Expression (정규표현식))

'Regular Expression'의 약자
이 모듈은 정규 표현식 매칭 작업을 제공
both patterns and strings to be searched can be Unicode strings (str) or 8-bit strings (bytes)
- Unicode strings and 8-bit strings cannot be mixed
- you cannot match/substitute a Unicode string w/ a bytes pattern or vice-versa → replacement string, pattern, and the search string must be of the same type
Regular Expressions use the backslash character ('\') to indicate special forms or to allow special characters to be used w/o invoking their special meaning
- this collides w/ Python's usage of the same character for the same purpose in string literals
- e.g., to match a literal backslash, one might have to write '\\\\' as the pattern string, b/c the regular expression must be \\, and each backslash must be expressed as \\ inside a regular Pyuthon string literal.
NOTE: any invalid escape sequences in Python's usage of the backslash in string literals now generate a SyntaxWarning and in the future this will become a SyntaxError
- this behaviour will happen even if it is a valid escape sequence for a regular expression

re.compile(pattern, flags=0)

- compile a regex pattern into a regex object, which can be used for matching using its match(), search() 등
- the expression's behaviour can be modified by specifying a flags value
  - values can be any of the flags variables, combined using bitwise OR (the | operator)
- sequence:

prog = re.compile(pattern)
result = prog.match(string)

# above is equivalent to
result = re.match(pattern, string)

using re.compile() and saving the resulting regex object for reuse is more efficient when the expression will be used several times in a single program

re.search(pattern, string, flags=0)

scan through string looking for the first location where the regex pattern produces a match, and return a corresponding Match
return None if no position in the string matches the pattern
NOTE: this is different from finding a zero-length match at some point in the string