My Python script runs fine on my laptop but crashes with 'ModuleNotFoundError' on the server. What am I missing?
My Python script runs fine on my laptop but crashes with 'ModuleNotFoundError' on the server.
Ask by Ashutosh Verma
Updated 09 Sep 2026
This is the classic 'it works on my machine' problem, and the honest answer is that your laptop and your server are not running the same Python. It sounds obvious, but it catches everyone at least once. On your laptop you probably installed the package into one environment, and on the server the script is being executed by a different interpreter that has no idea that package exists.
Start by asking both machines the same question. Run python -c "import sys; print(sys.executable)" on each. If the paths differ, or if one is Python 3.9 and the other 3.12, there is your answer. On Windows servers this gets worse because the Task Scheduler or IIS may be calling a system-wide Python while you installed packages into a user-level one.
The clean fix is a virtual environment that lives with the project. Create it with python -m venv venv, activate it, and install from a requirements.txt you generated on your laptop with pip freeze. Then make sure whatever launches the script (a scheduled task, a service, a web server) points at venv\Scripts\python.exe rather than plain 'python'.
A second thing to check: case sensitivity. If the server is Linux and your import says 'import Reportlab' but the package is 'reportlab', it will fail there and work on Windows. Small thing, huge headache.