Python regex '\s' vs '\\s'

Question

I have simple expression \\s and \\\\s . Both expression matches This is Sparta!! .

>>> re.findall('\\s',"This is Sparta")
[' ', ' ']
>>> re.findall('\s',"This is Sparta")
[' ', ' ']

I am confused here. \\ is used to escape special character and \\s represents white space but, how both are acting here?

Answer 1

Don't confuse python-level string-escaping and regex-level string-escaping. Since s is not an escapable character at python-level, the interpreter understand a string like "\\s" as the two characters "\\" and "s". Replace "s" with "n" (for example), and it understands it as the newline character.

'\s' == '\\s'
True
'\n' == '\\n'
False

Answer 2

\\ only escapes the following character if the escaped character is valid

>>> len('\s')
2
>>> len('\n')
1

compare with

>>> len('\\s')
2
>>> len('\\n')
2