Raw Strings in Python

In Python, raw strings are denoted by a prefix of r or R, as in r'...' or r"...". These strings interpret backslashes \ as literal characters, which is particularly beneficial when dealing with strings containing many backslashes, such as Windows paths or regular expression patterns.

Escape sequences

Python uses escape sequences, preceded by a backslash \ (like \t or \n), to represent characters that cannot be directly included in a string, such as tabs or line feeds.

• 2. Lexical analysis - String and Bytes literals — Python 3.11.3 documentation

s = 'a\tb\nA\tB'
print(s)
# a b
# A B

Raw strings interpret backslashes as literal characters

Strings prefixed with r or R, such as r'...' and r"...", are called raw strings and treat backslashes \ as literal characters. Unlike in regular strings, escape sequences are not given special treatment in raw strings.

rs = r'a\tb\nA\tB'
print(rs)
# a\tb\nA\tB

Despite their unique behavior, raw strings are not a distinct type. They are simply regular strings in which each backslash is represented as \\.

print(type(rs))
# <class 'str'>

print(rs == 'a\\tb\\nA\\tB')
# True

In a regular string, an escape sequence is interpreted as a single character. However, in a raw string, each backslash is considered a separate character.

• Get the length of a string (number of characters) in Python

s = 'a\tb\nA\tB'

print(len(s))
# 7

print(list(s))
# ['a', '\t', 'b', '\n', 'A', '\t', 'B']

rs = r'a\tb\nA\tB'

print(len(rs))
# 10

print(list(rs))
# ['a', '\\', 't', 'b', '\\', 'n', 'A', '\\', 't', 'B']

Windows paths

Raw strings are particularly useful for representing Windows paths, which are delimited by backslashes \. Instead of having to escape each backslash as \\ in a regular string, you can use raw strings to write them as is.

path = 'C:\\Windows\\system32\\cmd.exe'
rpath = r'C:\Windows\system32\cmd.exe'
print(path == rpath)
# True

However, be aware that a string ending with an odd number of backslashes will cause an error. To avoid this issue, you can either represent the entire path as a regular string (replacing each backslash with \\) or represent the path as a raw string up to the last backslash, then represent the last backslash as a regular string and concatenate them.

path2 = 'C:\\Windows\\system32\\'
# rpath2 = r'C:\Windows\system32\'
# SyntaxError: EOL while scanning string literal
rpath2 = r'C:\Windows\system32' + '\\'
print(path2 == rpath2)
# True

Convert regular strings to raw strings with repr()

You can use the built-in function repr() to transform a regular string into its raw string equivalent.

• Built-in Functions - repr() — Python 3.11.3 documentation

s = 'a\tb\nA\tB'

s_r = repr(s)
print(s_r)
# 'a\tb\nA\tB'

The string returned by repr() is enclosed in single quotes (').

print(list(s_r))
# ["'", 'a', '\\', 't', 'b', '\\', 'n', 'A', '\\', 't', 'B', "'"]

By using slicing, you can extract the raw string equivalent from the result of repr().

• How to slice a list, string, tuple in Python

rs = r'a\tb\nA\tB'

s_r2 = repr(s)[1:-1]
print(s_r2)
# a\tb\nA\tB

print(s_r2 == rs)
# True

print(r'\t' == repr('\t')[1:-1])
# True

Raw strings cannot end with an odd number of backslashes

A raw string ending with an odd number of backslashes will lead to an error, as the backslashes escape the trailing quotation marks (' or ").

• Design and History FAQ - Why can't raw strings (r-strings) end with a backslash? — Python 3.11.3 documentation

# print(r'\')
# SyntaxError: EOL while scanning string literal

print(r'\\')
# \\

# print(r'\\\')
# SyntaxError: EOL while scanning string literal