Python Regex Tester

• Live matches + capture groups, with copyable re.search / re.findall Python code
• Always use raw strings in Python: r"\d+" — otherwise Python eats your backslashes first
• Python named groups are (?P<name>…); this tester also accepts JS's (?<name>…)
• Python lookbehind must be fixed-width — (?<=abc) works, (?<=a+) does not
• re.match anchors at string start; re.search scans — findall is this tester's g flag

Frequently Asked Questions

Why does everyone use r"" raw strings for Python regex?

Because Python's normal string literals process backslashes before the regex engine sees them: "\d" survives only by luck, and "\b" silently becomes a backspace character instead of a word boundary. Raw strings (r"\d", r"\b") pass every backslash straight through to re. Always write regex patterns as raw strings.

Why does my lookbehind fail in Python but work here?

Python's re module only supports fixed-width lookbehind: (?<=abc) is fine, but (?<=a+) or (?<=ab|abc) raise an error. Rewrite with a capture group ((a+)(target) and take group 2), or install the third-party 'regex' module, which supports variable-width lookbehind.

What's the Python equivalent of the g flag?

re.findall(pattern, s) returns all matches as strings (or tuples when you have groups); re.finditer returns an iterator of match objects. For replace-all, re.sub replaces every occurrence by default — the opposite of JavaScript, where replace without g does only the first.

Do (?P<name>) and (?<name>) both work?

In Python, only (?P<name>…) — the P is required, and backreferences are (?P=name). This tester (JS engine) uses (?<name>…). The generated Python snippet uses the correct (?P<name>) spelling automatically when you copy code.

Is this tester free and private?

Yes — free, no signup, no limits, and 100% client-side: patterns and test strings are processed in your browser and never sent to a server.