Python Raw Strings — Why r'\d+'

The double-escape problem

In Python strings, the backslash \ is the escape character. '\n' is a newline; '\t' is a tab; '\b' is the ASCII bell.

In regex patterns, the backslash is ALSO the escape character. \d is a digit; \b is a word boundary; \. is a literal dot.

Without raw strings, you'd have to write '\\d' for the regex digit class — one backslash for Python's string parser, another for regex. Annoying and error-prone.

Raw strings disable Python's interpretation

Prefix a string literal with r: r'\d+'. Now Python doesn't interpret backslashes — they pass through to regex unchanged. r'\b\w+\b' means exactly what it looks like.

The bug class without raw strings

'\b' in Python is the ASCII bell character (chr(8)). If you write re.search('\bword', text), Python sees '\x08word' as the pattern — definitely not what you wanted. Some patterns happen to work without raw strings ('\d' isn't a valid Python escape so it stays as two chars), but relying on this is fragile.

Always use raw strings for regex patterns in Python. No exceptions.

F-strings for dynamic patterns

To interpolate variables, combine raw and f-string: rf'\b{word}\b'. Or use re.escape when interpolating user input: rf'\b{re.escape(word)}\b'.

Code

Raw strings save you·python

import re

# Without raw — Python interprets \b as bell
bool(re.search('\bword', 'a word here'))   # False (probably wrong!)
bool(re.search(r'\bword', 'a word here'))  # True

# Raw + f-string for variable interpolation
name = 'pippa'
pattern = rf'\b{name}\b'  # r'\bpippa\b'
bool(re.search(pattern, 'hi pippa'))  # True

# When interpolating UNTRUSTED input, escape it
user_query = 'foo.bar'  # the user typed a literal string
safe = re.escape(user_query)  # 'foo\\.bar'
pattern = rf'\b{safe}\b'
bool(re.search(pattern, 'we found foo.bar in the data'))  # True

# Raw strings can't end in odd number of backslashes — Python quirk
# r'\\' is fine (2 backslashes)
# r'\' is a SyntaxError
# Workaround: '\\' (escaped) or r'\\' followed by literal

Python Raw Strings — Why r'\d+'

The double-escape problem

Raw strings disable Python's interpretation

The bug class without raw strings

F-strings for dynamic patterns

Code

External links

Exercise

Progress

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