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‎dest/README.md‎

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# Regex Inverter
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This directory contains a web-based Regex Inverter tool powered by [PyScript](https://pyscript.net/) and `pyparsing`.
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## Overview
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The Regex Inverter allows you to enter a regular expression and generate all possible strings that match it. It is particularly useful for visualizing the expansion of character classes, repetitions, and alternatives.
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### Key Features:
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- **Expansion of Regex Patterns:** Generates matching strings for patterns like `[A-Z]{3}\d{3}`.
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- **Client-Side Processing:** All computations happen in your browser using PyScript, so no data is sent to a server.
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- **Progress Tracking:** Shows the total count of possible matches, even if they exceed the display limit.
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### Supported Syntax:
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- Character sets: `[a-z]`, `[0-9A-F]`, `[^0-9]`
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- Repetitions: `{n}`, `{min,max}`, `{,max}`
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- Alternatives: `apple|orange`
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- Groups: `(abc|def)`
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- Macros: `\d`, `\w`, `\s`, `\D`, `\W`, `\S`
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- Dot: `.` (matches printable characters)
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### Constraints:
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- **Unbounded operators `+` and `*` are not supported.** You must use explicit range repetitions like `{1,10}` instead of `+` to prevent infinite or excessively large result sets that would crash the browser.
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## Files
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- `index.html`: The web interface and PyScript configuration.
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- `inv_regex.py`: The core inversion logic using `pyparsing`.
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## How to Run Locally
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To run the Regex Inverter on your own machine:
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1. Open a terminal or command prompt.
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2. Navigate to this directory:
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```bash
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cd examples/regex_inverter
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```
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3. Start a local Python web server:
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```bash
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python -m http.server
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```
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4. Open your web browser and go to:
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[http://localhost:8000](http://localhost:8000)
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## Deployment
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To deploy this to a web server:
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1. Upload both `index.html` and `inv_regex.py` to the same directory on your web server.
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2. Ensure your server is configured to serve `.html` files (most are by default).
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3. Access the `index.html` file through its URL.
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Since this is a static site (using PyScript to run Python in the browser), you can even host it on GitHub Pages or any other static site hosting service.

‎dest/index.html‎

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<!DOCTYPE html>
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<html lang="en">
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<head>
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<meta charset="UTF-8">
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<meta name="viewport" content="width=device-width, initial-scale=1.0">
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<title>PyParsing Regex Inverter</title>
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<link rel="stylesheet" href="https://pyscript.net/releases/2025.11.1/core.css">
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<script type="module" src="https://pyscript.net/releases/2025.11.1/core.js"></script>
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<style>
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body { font-family: sans-serif; margin: 2em; }
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#regex-input { width: 300px; }
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#output { width: 100%; height: 400px; margin-top: 1em; font-family: monospace; white-space: pre; border: 1px solid #ccc; padding: 0.5em; overflow: auto; }
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.controls { margin-bottom: 1em; }
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table { border-collapse: collapse; width: 100%; }
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table th, table td { border: 1px solid #ddd; padding: 8px; text-align: left; }
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table th { background-color: #f2f2f2; }
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</style>
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</head>
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<body>
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<h1>Regex Inverter</h1>
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<h4>by Paul McGuire, January 2026</h4>
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<details>
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<summary>Description</summary>
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<div>
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<p>This page allows you to invert a regular expression, generating all strings that match it.</p>
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<p><strong>Instructions:</strong> Enter a regular expression in the "Regex" field and specify the maximum number of results you want to see (up to 100,000,000). Click "Invert" or press Enter to generate the matching strings.</p>
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<p><strong>Constraints:</strong></p>
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<ul>
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<li>Unbounded repetition operators <code>+</code> and <code>*</code> are <strong>not supported</strong>.</li>
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<li>Replace <code>+</code> or <code>*</code> with explicit <code>{n}</code> or <code>{min,max}</code> repetition operators (e.g., use an explicit repetition like <code>[A-Z]{1,4}</code> instead of <code>[A-Z]+</code>, or <code>[A-Z]{,4}</code> instead of <code>[A-Z]*</code>).</li>
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</ul>
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<p><strong>Note:</strong> Complex regular expressions or those with large repetition counts may take some time to process.</p>
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</div>
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</details>
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<p>
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<details>
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<summary>Examples</summary>
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<div>
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<p>Here are some example regular expressions to try:</p>
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<table>
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<thead>
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<tr><th>Description</th><th>Regex</th></tr>
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</thead>
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<tr>
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<td>Match one uppercase letter followed by three digits</td>
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<td><pre>[A-Z]-\d{3}</pre></td>
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</tr>
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<tr>
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<td>Time of day (HH:MM:SS)</td>
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<td><pre>(2[0-3]|[01]\d):([0-5]\d):([0-5]\d)</pre></td>
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</tr>
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<tr>
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<td>8-bit binary numbers</td>
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<td><pre>[01]{8}</pre></td>
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</tr>
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<tr>
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<td>Integer from 0 to 99</td>
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<td><pre>[1-9]?\d</pre></td>
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</tr>
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<tr>
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<td>Integer from 0 to 255</td>
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<td><pre>25[0-5]|2[0-4]\d|1\d{2}|[1-9]\d|\d</pre></td>
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</tr>
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<tr>
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<td>Roman Numerals to 50</td>
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<td><pre>(X{,3}|XL)(I{,3}|IV|VI{,3}|IX)|L</pre></td>
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</tr>
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<tr>
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<td>IPv4 addresses in 192.168.0.0/16</td>
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<td><pre>192\.168(\.((25[0-5]|2[0-4]\d|1\d{2}|[1-9]\d|\d))){2}</pre></td>
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</tr>
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<tr>
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<td>MAC address</td>
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<td><pre>[0-9A-Fa-f]{2}([:-][0-9A-Fa-f]{2}){5}</pre></td>
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</tr>
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<tr>
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<td>UUID</td>
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<td><pre>[0-9A-F]{8}(-[0-9A-F]{4}){3}-[0-9A-F]{12}</pre></td>
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</tr>
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<tr>
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<td>Original US Area codes</td>
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<td><pre>[2-9][10][2-9]</pre></td>
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</tr>
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</table>
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</div>
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</details>
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<p>Enter a regular expression to see its matching strings.</p>
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<div class="controls">
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<label for="regex-input">Regex:</label>
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<input type="text" id="regex-input" placeholder="e.g. [A-Z]-\d{3}" value="">
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<label for="max-results">Max results:</label>
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<input type="number" id="max-results" value="200" min="1" style="width: 60px;">
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<button id="invert-btn" py-click="do_invert">Invert</button>
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<button id="cancel-btn" py-click="cancel_invert" style="display: none;">Cancel</button>
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</div>
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<div id="status"></div>
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<textarea id="output" readonly></textarea>
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<p>GitHub repo for this page <a href="https://github.com/ptmcg/regex_inverter.git" target="_blank">regex-inverter</a></p>
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<p>Powered by <a href="https://pyscript.net" target="_blank">PyScript</a> and <a href="https://pypi.org/project/pyparsing/" target="_blank">pyparsing</a></p>
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<py-config>
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packages = ["pyparsing"]
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[[fetch]]
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files = ["inv_regex.py"]
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</py-config>
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<script type="py">
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from pyscript import document
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from inv_regex import invert, count
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import pyparsing
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import itertools
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import asyncio
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is_cancelled = False
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def cancel_invert(event):
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global is_cancelled
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is_cancelled = True
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async def do_invert(event):
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global is_cancelled
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is_cancelled = False
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regex = document.querySelector("#regex-input").value.strip()
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if not regex:
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return
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try:
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max_results = int(document.querySelector("#max-results").value)
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except ValueError:
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max_results = 200
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if max_results > 100_000_000:
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max_results = 100_000_000
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document.querySelector("#max-results").value = 100_000_000
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output_area = document.querySelector("#output")
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status_div = document.querySelector("#status")
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cancel_btn = document.querySelector("#cancel-btn")
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output_area.value = ""
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status_div.innerText = "Processing..."
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# Use a small delay to allow status to update in the UI
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await asyncio.sleep(0.1)
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try:
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# Get up to max_results items using an iterator
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invert_iter = invert(regex)
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results = list(itertools.islice(invert_iter, max_results))
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num_shown = len(results)
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output_area.value = "\n".join(results)
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if num_shown == max_results:
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cancel_btn.style.display = "inline"
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await asyncio.sleep(0.1)
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# Count the remaining items in the iterator
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remaining_count = 0
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for i, _ in enumerate(invert_iter, 1):
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remaining_count = i
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if i % 100_000 == 0:
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status_div.innerText = f"Counting matches... {num_shown + i:,} found so far"
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await asyncio.sleep(0)
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if is_cancelled:
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status_div.innerText += " (cancelled)"
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break
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total_count = num_shown + remaining_count
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if not is_cancelled:
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status_div.innerText = f"Total matching strings: {total_count:,}"
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if total_count > max_results:
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status_div.innerText += f" (showing first {max_results:,})"
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except pyparsing.ParseBaseException as pe:
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status_div.innerText = "Error"
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output_area.value = f"Parse Error: {pe.msg}\n{pe.explain(depth=0)}"
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except Exception as e:
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status_div.innerText = "Error"
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output_area.value = f"Error: {str(e)}"
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finally:
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cancel_btn.style.display = "none"
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# Add event listener for Enter key in input box
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def on_keypress(event):
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if event.key == "Enter":
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asyncio.create_task(do_invert(None))
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document.querySelector("#regex-input").onkeypress = on_keypress
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document.querySelector("#max-results").onkeypress = on_keypress
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</script>
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</body>
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</html>

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