1. Limitations of OnlineGDB
OnlineGDB is convenient for quickly testing code online, but it doesn't allow the installation of external libraries like `treelib`. This makes it limited for projects that require additional packages. You can run basic Python code, but as soon as you try to import a library not included by default, you're blocked.
2. More Flexible Alternatives
For a simple online environment capable of installing libraries, the most reliable options are **Google Colab** (where you can use `!pip install treelib`), **PythonAnywhere** (which accepts `pip install` in your local environment), or some online compilers with built-in libraries (often limited to the most popular ones like NumPy or Pandas). Programiz, for example, doesn't allow adding external packages, so it's unsuitable for `treelib`.
3. Practical Recommendation
If your criterion is a "clean" and minimalist environment, but with the freedom to install any library, **Google Colab** remains the best option: free, simple to use, and you control your space without being overrun by other projects. If you prefer offline, **Thonny** is a lightweight IDE that requires no registration and lets you install packages easily. This way, you combine simplicity and flexibility according to your needs.