Confusion escaping single quotes in a single-quoted raw string literal
python, regex, string
Solution
No, they should not. A raw string literal does let you escape quotes, but the backslashes will be included:
>>> r"\'"
"\\'"
where Python echoes the resulting string as a string literal with the backslash escaped.
This is explicitly documented behaviour of the raw string literal syntax:
When an `'r'` or `'R'` prefix is present, a character following a backslash is included in the string without change, and all backslashes are left in the string. For example, the string literal `r"\n"` consists of two characters: a backslash and a lowercase `'n'`. String quotes can be escaped with a backslash, but the backslash remains in the string; for example, `r"\""` is a valid string literal consisting of two characters: a backslash and a double quote; `r"\"` is not a valid string literal (even a raw string cannot end in an odd number of backslashes).
If you didn't use a raw string literal for the second parameter, Python would interpret the `\digit` combination as octal byte values:
>>> '\0'
'\x00'
You can construct the same string without raw string literals with doubling the backslash:
>>> '\\1\'\'\\2'
"\\1''\\2"
Problem
The following works as expected: ``` >>> print re.sub('(\w)"(\W)', r"\1''\2", 'The "raw string literal" is a special case of a "string literal".') The "raw string literal'' is a special case of a "string literal''. ``` Since I wanted to use single quotes in the replacement expression (is that the correct terminology?), I quoted it using double quotes. But then for my edification I tried using single quotes in the replacement expression and can't understand the results: ``` >>> print re.sub('(\w)"(\W)', r'\1\'\'\2', 'The "raw string literal" is a special case of a "string literal".') The "raw string literal\'\' is a special case of a "string literal\'\'. ``` Shouldn't the two forms produce exactly the same output? So, my questions are: - How do I escape a single quote in a single-quoted raw string? - How do I escape a double quote in a double-quoted raw string? - Why is it that in the first parameter to `re.sub()` I didn't have to use raw string, but in the second parameter I have to. Both seem like string representations of regexes to this Python noob. If it makes a difference, am using Python 2.7.5 on Mac OS X (10.9, Mavericks).