slow code in Python

[Edgar458g]

Hi everyone.
I’m new to Python and ran into a small problem.
I wrote a script that works fine with small files, but when the file gets bigger, everything becomes very slow. No errors, just takes a long time to finish.
Is this usually about loops or reading the file line by line?
What is the first thing I should check to make it faster?

Thanks in advance.

[sophiasmith]

Hi! Slow Python scripts with big files are usually caused by inefficient loops or reading/processing line by line. First, check how you handle the file and avoid repeated heavy operations. Using efficient data structures and profiling your code with cProfile can help find the bottleneck.

Infinite Craft

[evelynwang]

Yeah, that’s a pretty typical thing when you move from small to bigger files. sports games
In most cases it is about what you’re doing inside loops, not just the file reading itself. Reading line by line is usually fine in Python, but if you’re doing something expensive for every line (or worse, looping over the data multiple times), it adds up fast.
When I ran into this early on, the biggest slowdown was me accidentally reprocessing the same data again and again inside loops. Also stuff like checking membership in a list instead of using a set made a huge difference once the data got bigger.
What helped me was just timing different parts of the code to see where it slows down. You’ll usually find one specific spot that’s the bottleneck.
If you paste a bit of your code, it’s a lot easier to point out what’s causing it.

[scaredsteal]

First, use a profiler (cProfile) to pinpoint which code is slow instead of guessing.
Then, check how the file is read—read line by line instead of loading the entire file into memory.
Next, see if there are any heavy operations within the loop (such as string manipulation, searching, or regex).
Finally, check the algorithm (avoid nested loops or searching through large lists; use sets/dicts instead). retro bowl