← Errors
re.error is raised when a string passed to a function in the re module is not a valid regular expression. The error message includes the position of the syntax problem in the pattern, making it straightforward to locate and fix.
Why it happens
- •Unclosed parentheses or brackets in the pattern.
- •An invalid escape sequence like \p or \q that is not a recognized regex token.
- •A quantifier like * or + applied to nothing (at the start of the pattern).
- •Unmatched curly braces in a repetition quantifier like {3,.
Examples
Python
Code that triggers the error
import re
re.compile(r"(unclosed group")Error output
re.error: missing ), unterminated subpattern at position 0
How to fix it
Test regex patterns interactively with a tool like regex101.com before embedding them in code. Always wrap re.compile() in a try/except re.error block when the pattern comes from user input. Use raw strings (r'...') to avoid Python string escape conflicts.
Fixed code
import re
try:
pattern = re.compile(r"(closed group)")
match = pattern.search("closed group found")
print(match.group() if match else "no match")
except re.error as e:
print(f"Invalid regex: {e}")Related errors
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