# Python Regex Tester (re module)

Test Python re patterns online: (?P…) named groups, (?P=name) backreferences, VERBOSE patterns, findall behavior, and \\g replace templates — plus ready-to-paste Python code.

> Canonical page: https://elysiatools.com/en/tools/python-regex-tester

- **Category:** Development

- **Keywords:** python regex tester, python regular expression online, re module, re.findall, re.sub, (?P), python regex online

## Overview

A regex tester for Python\\u0027s built-in re module. Write the pattern exactly as in Python — named groups (?P…), the named backreference (?P=tag), VERBOSE free-spacing with # comments, re.IGNORECASE / MULTILINE / DOTALL flags — and it is translated to the platform\\u0027s ECMAScript engine and executed against your test string. You get every match (findall/finditer style with the g toggle), a capture-group table with names, and a re.sub-style replace preview where \\1, \\g<1> and \\g templates are translated for the preview. Ready-to-paste Python code with the right re.\* flags and match.group(\\u0027name\\u0027) access is generated. Python-specific semantics are honored: \\d \\w \\s are Unicode by default for str patterns (uncheck to emulate re.ASCII), possessive quantifiers and atomic groups (Python 3.11+) are emulated with lookahead-capture, and .NET-style (?…) syntax is rejected with a hint to use (?P…) — exactly as Python would.

## Inputs

- **Pattern** (text): (?P\\d{4})-(?P\\d{2})
- **Test string** (textarea): Paste the text to match against…
- **i — IGNORECASE** (checkbox)
- **m — MULTILINE** (checkbox)
- **s — DOTALL** (checkbox)
- **x — VERBOSE** (checkbox)
- **a — ASCII** (checkbox)
- **g — find all (findall)** (checkbox)
- **Replacement template (optional)** (text): \\g / \\1
- **Unicode character classes (\d \w \s match Unicode)** (checkbox)

## When to use

- Debugging complex patterns that use Python-specific named groups (?P...) or backreferences (?P=name).
- Previewing string transformations with re.sub using \\g or numbered replacement templates.
- Formulating readable multiline regular expressions using the re.VERBOSE flag with inline comments.

## How it works

- Enter your regular expression pattern using Python re syntax alongside your test subject string.
- Toggle standard Python flags such as IGNORECASE (i), MULTILINE (m), DOTALL (s), VERBOSE (x), or ASCII (a).
- Optionally provide a replacement template (\\g or \\1) to evaluate re.sub replacement results.
- Inspect the match list, named capture group tables, replacement output, and generated Python code snippets.

## Use cases

- Validating structured log parser expressions that extract variables into named dictionary fields.
- Testing string formatting templates that reorder extracted substrings using re.sub.
- Writing robust HTML or XML tag matching patterns using named backreferences.

## Frequently asked questions

### How does named group syntax differ from standard PCRE or JavaScript in Python?

Python uses (?P...) for defining named capture groups and (?P=name) for backreferences, whereas other engines often use (?...).

### Can I use comments and multi-line formatting in my regex?

Yes, enabling the VERBOSE (x) flag allows you to add whitespace and # comments within your regular expression pattern.

### How do I reference named capture groups in the replacement field?

Use Python's \\g syntax or standard numbered references like \\1 or \\g<1> in the replacement template input.

### Are character classes like \d and \w matching Unicode characters by default?

Yes, standard string patterns in Python match Unicode by default; you can enable the ASCII (a) flag to restrict them to ASCII ranges.

### Does this tool generate executable Python code?

Yes, it automatically generates ready-to-paste Python code snippets including the specified re flags and named group access calls.

## Related tools

- [Regex Debugger](https://elysiatools.com/en/tools/regex-debugger): Step through how a regular expression matches a string position by position: visualize match attempts, partial successes, backtracks, and captures — a learning tool for understanding regex behavior, not just the final result
- [C# Regex Tester (.NET)](https://elysiatools.com/en/tools/csharp-regex-tester): Test .NET/C# regular expressions online with named groups ((?…)), IgnoreCase/Multiline/Singleline options, match highlighting, capture-group tables, a ready-to-paste C# snippet and an IgnorePatternWhitespace preview.
- [Java Regex Tester](https://elysiatools.com/en/tools/java-regex-tester): Test java.util.regex patterns online: (?…) named groups, possessive quantifiers and atomic groups, Pattern flags, ASCII vs UNICODE\_CHARACTER\_CLASS \\d semantics, and ready-to-paste Java code.
- [AI Regex Explainer](https://elysiatools.com/en/tools/ai-regex-explainer): Use AI to break down regular expressions into readable explanations
- [PCRE2 Regex Tester](https://elysiatools.com/en/tools/pcre-regex-tester): Test PCRE2 patterns online: every named-group syntax ((?P), (?), (\\u0027n\\u0027)), possessive quantifiers, atomic groups, \\A \\z \\h shorthands, plus pcre2grep and C API snippets.
- [Multi-Pattern Matcher](https://elysiatools.com/en/tools/multi-pattern-matcher): Match multiple regex patterns against text in one operation
- [Named Group Tester](https://elysiatools.com/en/tools/named-group-tester): Parse and display named capture groups from regex patterns
- [Regex Tester](https://elysiatools.com/en/tools/regex-tester): Test regular expressions against text

## Samples

- [Web Image Processing Python Samples](https://elysiatools.com/en/samples/web-image-processing-python): Web Python image processing examples using PIL/Pillow including reading, saving, resizing, and format conversion
- [Regex Replace Samples](https://elysiatools.com/en/samples/regex-replace): Collection of common and useful regex replacement patterns for text transformation and data cleaning
- [Common Regex Patterns](https://elysiatools.com/en/samples/regex-samples): Commonly used regular expression patterns for validation and matching
- [Web String Processing Python Samples](https://elysiatools.com/en/samples/web-string-processing-python): Web Python string processing examples including string split/join, regular expressions, and string replacement