What's the difference between an r string (r'foobar') and a normal string ('foobar') in Python? Is r'string' a regex string?
I've tried the following and there aren't any effects on my regex matches:
>>> import re >>> n = 3 >>> rgx = '(?=('+'\S'*n+'))' >>> x = 'foobar' >>> re.findall(rgx,x) ['foo', 'oob', 'oba', 'bar'] >>> >>> rgx2 = r'(?=('+'\S'*n+'))' >>> re.findall(rgx2,x) ['foo', 'oob', 'oba', 'bar'] >>> >>> rgx3 = r'(?=(\S\S\S))' >>> re.findall(rgx3,x) ['foo', 'oob', 'oba', 'bar'] r doesn't signify a "regex string"; it means "raw string". As per the docs:
String literals may optionally be prefixed with a letter
'r'or'R'; such strings are called raw strings and use different rules for interpreting backslash escape sequences.
They are commonly used (and recommended) for regular expressions because regex and non-raw strings both use backslashes as an escape character. For example, to match a literal backslash with a regex in a normal string would be '\\\\'; using a raw string, it's just '\\'.
The difference would become apparent in cases when you have backslash escapes:
>>> s="foobar" >>> import re >>> re.sub('(o)\1', '', s) # Using the backreference has no effect here as it's interpreted as a literal escaped 1 'foobar' >>> re.sub(r'(o)\1', '', s) # Using the backreference works! 'fbar' >>> re.sub('(o)\\1', '', s) # You need to escape the backslash here 'fbar' Quoting from String literal:
A few languages provide a method of specifying that a literal is to be processed without any language-specific interpretation. This avoids the need for escaping, and yields more legible strings.
You might also want to refer to Lexical Analysis.
