 <p>Fromt the <a href="http://docs.python.org/2/reference/lexical_analysis.html#string-literals" rel="nofollow">docs</a>:</p> <blockquote> <p>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). Specifically, a raw string cannot end in a single backslash (since the backslash would escape the following quote character). Note also that a single backslash followed by a newline is interpreted as those two characters as part of the string, not as a line continuation.</p> </blockquote> <p><strong>Specifically, a raw string cannot end in a single backslash (since the backslash would escape the following quote character)</strong></p>