📅 ICS Event Merger

Leveraging Copilot with prompt enginnering to make a quick .ics merger.

A simple Python tool to merge multiple .ics calendar files into one or more combined files — perfect for importing into Google Calendar without duplicates.

I made this because I use a booking system for certain appointments that gave me single .ics file downloads rather than connecting to a calendar service directly. In order to bulk import events into Google Calendar (because there is no way to mass drop .ics files into GCal at this time...) I had to merge all the files into one, then GCal would do the bulk import.

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✅ Features

• 🖱️ Drag-and-drop GUI — drop a pile of .ics files in and click merge
• 📂 Merge all .ics files from a directory (CLI)
• 🧠 Smart deduplication (prevents duplicate events)
• 🔁 Safe to re-run (remembers already processed events)
• 📦 Automatically splits large outputs into smaller files
• 📍 Saves output to the directory you choose

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📦 Installation

🟢 New to Python? Just follow Option A below — copy each command into the Terminal app and press Enter, one line at a time. You don't need to know any Python to use this tool.

Before you start

You need Python 3.9 or newer. Check what you have:

python3 --version

• If it prints something like Python 3.12.4, you're good to go.
• If it says command not found, install Python from python.org/downloads (Mac users with Homebrew can run brew install python instead).

💻 Opening the Terminal: on macOS, press Cmd + Space, type Terminal, and press Enter.

Option A — step by step (recommended)

These commands make a self-contained copy of the tool, so nothing else on your computer is affected. Run them one at a time, in order:

# 1. Download the project and move into its folder
git clone https://github.com/dcwell/Python-ics-Merger.git
cd Python-ics-Merger

# 2. Create a "virtual environment" — a private sandbox for this tool's parts
python3 -m venv .venv

# 3. Turn the sandbox on  (you'll see "(.venv)" appear in your prompt)
source .venv/bin/activate        # macOS / Linux
# .venv\Scripts\Activate.ps1     # Windows (PowerShell)

# 4. Install the tool into the sandbox
pip install ".[gui]"

Done — the ics-merger command is now ready (jump to Usage below).

📦 No git? On the GitHub page, click the green Code button → Download ZIP, unzip it, then start from step 2 inside the unzipped folder.

🔁 Coming back later? In a new Terminal you don't reinstall — just cd back into the project folder and run source .venv/bin/activate again to switch the sandbox on. Run deactivate to switch it off; delete the .venv folder to remove everything.

⚠️ Two things that trip people up:

• Keep the quotes: pip install ".[gui]" (some shells misread a bare [ ]).
• Run it inside the folder that contains pyproject.toml — check with ls pyproject.toml.

Option B — pipx (optional, more convenient long-term)

Skip this if you already did Option A. Once you're comfortable, pipx installs the ics-merger command so it works from any folder — no sandbox to switch on each time:

cd Python-ics-Merger
pipx install ".[gui]"

About the GUI extra

The [gui] extra pulls in tkinterdnd2 for true drag-and-drop; without it the GUI falls back to a native file picker.

🍎 Tkinter ships with most Python installs. On Homebrew Python you may need to add it — install the package matching your Python version, e.g. brew install python-tk@3.14.

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🚀 Usage

Step 1 — know your run command

What you type depends on how you installed it (from Installation above):

If you installed with…	…run the tool with	Reminder
Option A — venv + pip	ics-merger	Activate the venv first: source .venv/bin/activate
Option B — pipx	ics-merger	Works from any folder
No install — from a clone	python ICS_Merger.py	Run from the project folder (dependencies must be installed)

python -m ics_merger is an equivalent alternative anywhere the package is installed.

Step 2 — choose GUI or command line

The argument decides what happens — and it's the same for whichever command you picked above.

🖥️ GUI (drag-and-drop) — run it with no argument:

ics-merger

A window opens; drag .ics files (or whole folders) in, click Merge ▶, and pick an output folder. (The GUI needs Tkinter — see Installation. Without tkinterdnd2 it falls back to a native file picker.)

⌨️ Command line — give it a folder path:

ics-merger /path/to/folder

Every .ics file in that folder is merged, with the output written to the same folder.

Using the no-install launcher instead? Swap ics-merger for python ICS_Merger.py in the two examples above (e.g. python ICS_Merger.py /path/to/folder).

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📁 Output

Merged files and the dedup cache are written into the same input directory:

my_calendars/
├── calendar1.ics          # your original files (left untouched)
├── calendar2.ics
├── merged_events_1.ics    # combined output (up to 500 events each)
├── merged_events_2.ics
└── seen_events.json       # cache of processed events (enables safe re-runs)

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🗂️ Project Structure

Python-ics-Merger/
├── ICS_Merger.py              # no-install launcher (delegates to the package)
├── pyproject.toml             # packaging, dependencies, console script, tooling
├── src/
│   └── ics_merger/
│       ├── __init__.py        # package metadata (__version__)
│       ├── __main__.py        # enables `python -m ics_merger`
│       ├── cli.py             # entry-point logic (main)
│       ├── merger.py          # core engine — scanning, dedup cache, chunking
│       └── gui.py             # drag-and-drop window (+ file-picker fallback)
├── tests/
│   └── test_merger.py         # pytest unit tests
├── .github/workflows/ci.yml   # CI: ruff lint + pytest matrix
├── LICENSE
└── README.md

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🧠 How It Works

1. Every .ics file in the directory is scanned for events (VEVENT).
2. Each event gets a signature built from its UID, start, end, and summary.
3. Signatures are checked against seen_events.json; duplicates are skipped.
4. New events are written to merged_events_*.ics files, split into chunks of up to 500 events (configurable via CHUNK_SIZE in src/ics_merger/merger.py).
5. The cache is updated so re-running never re-adds the same events.

💡 To force a clean re-merge, delete seen_events.json and the generated merged_events_*.ics files, then run the tool again.

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📥 Importing into Google Calendar

1. Open Google Calendar on the web.
2. Go to Settings ⚙️ → Import & Export.
3. Under Import, select a merged_events_*.ics file.
4. Choose the destination calendar and click Import.
5. Repeat for each merged_events_*.ics file if more than one was created.

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📝 Notes

• Your original .ics files are never modified or deleted.
• In CLI mode, output and the cache go to the input directory; in GUI mode you pick the output folder.
• Adjust CHUNK_SIZE in src/ics_merger/merger.py to change events-per-file.

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🛠️ Troubleshooting

ModuleNotFoundError: No module named 'icalendar' Your virtual environment isn't active (or your editor is running a different Python). Activate it with source .venv/bin/activate, then confirm with which python — the path should be inside .venv. In VS Code, run Python: Select Interpreter from the Command Palette and choose the .venv.

Directory '.[gui]' is not installable. Neither 'setup.py' nor 'pyproject.toml' found. You're running pip from the wrong folder. cd into the directory that contains pyproject.toml (check with ls pyproject.toml), then re-run the install.

The GUI won't open / No module named '_tkinter' Tkinter isn't bundled with your Python build. On macOS Homebrew Python, install the package matching your Python version (e.g. brew install python-tk@3.14), then try again. Command-line mode works without Tkinter.

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🧪 Development

Set up an editable install with the dev tools (pytest + ruff):

pip install -e ".[dev]"

Run the test suite and linter:

pytest
ruff check .

Continuous integration (GitHub Actions) runs the same checks across Python 3.9, 3.11, and 3.12 on every push and pull request — see .github/workflows/ci.yml.

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🏷️ Versioning

This project follows Semantic Versioning (MAJOR.MINOR.PATCH):

• MAJOR — incompatible or breaking changes
• MINOR — new features, backward compatible
• PATCH — bug fixes, backward compatible

The version is single-sourced from __version__ in src/ics_merger/__init__.py (read automatically by pyproject.toml). When releasing a new version, bump that value, add a row to the changelog below, update the badge, and tag the release:

git tag -a v1.1.0 -m "v1.1.0"
git push origin v1.1.0

💡 Pushing a tag lets you publish a matching GitHub Release, which then appears automatically under the repository's Releases section.

📜 Changelog

Version	Date	Changes
1.1.0	2026-06-21	Add drag-and-drop GUI; adopt a src/ package layout with pyproject.toml packaging, an ics-merger console script, pytest tests, and GitHub Actions CI.
1.0.0	2026-06-21	Initial release: directory merge, dedup cache, and chunked output.

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📄 License

Released under the MIT License.