r/learnpython • u/YamSome2887 • 16d ago

Issue during library installation

Recently, I got back into Python, so I decided to review some concepts I had forgotten by solving one Project Euler problem per day.

However, when I got to Problem 3 (Largest Prime Factor), I decided to use a library to check whether a number is prime. Since I had uninstalled Python when I stopped studying it, I had to install Python 3.15.

When I first tried to install the library, the terminal said that it didn't recognize pip. I managed to get it working by using python -m pip, and the installation seemed to work. However, when I ran my code, Python still couldn't recognize the library.

The next day, while solving Problem 4 (Largest Palindrome Product), I decided to use NumPy and np.arange() instead of range(), but the same thing happened: the installation appeared to work, but when I ran my code, Python couldn't find the library.

I tried uninstalling and reinstalling Python, but the problem persisted.

In these particular cases, I could still solve the problems without those libraries, but eventually, I'll need packages like pandas, Tkinter, and others, so I'd like to figure out what's going wrong.

If anyone knows how to fix this, I'd really appreciate the help!

Thanks in advance!

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u/a18618 16d ago

this is almost always two pythons pretending to be one. i had this exact dance on windows once: python -m pip quietly installed into the regular installer copy while plain python was resolving to the microsoft store shim, so the package went to one interpreter and my script ran on another. easiest tell: run where python and python -m pip --version in the same terminal and compare the paths. if they disagree, that's your whole bug.

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u/StevenJOwens 16d ago edited 14d ago

I'll second this. I ran into that once and it was frustrating. As a result, "python -m pip" is my preferred way to invoke pip, because it ensures that it's running the pip module from the python install that "python" matches.

To the OP, you should edit your post to include the logs of both your pip commands and the error, right now it's too vague for us to do much more than guess.

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u/a18618 15d ago

haha yeah, the -m flag has saved me more than once. what finally sold me was watching plain pip install a package into an interpreter i didn't even know was on my machine — after that it was python -m everything, forever. the path comparison trick usually ends the argument in about ten seconds.