Szathmáry László honlapja @ DEIK | Nim2 / From Nim, call Python

It's possible to call Python code from your Nim program. It can be done with a 3rd-party library called nimpy:

$ nimble install nimpy

nimpy uses the system-wide Python that was available at compile time. Let's check what is used:

Which python is used?
import sys print(sys.version) print(sys.executable) # '/usr/bin/python3'	import nimpy proc main() = let sys = pyImport("sys") echo sys.version.to(string) echo sys.executable.to(string) # '/usr/bin/python3' main()

Same output in both cases:

3.14.3 (main, Feb 13 2026, 15:31:44) [GCC 15.2.1 20260209]
/usr/bin/python3

Create a custom Python module

Let's create a custom Python module with a function and call this function from Nim.

$ tree
.
├── main.nim
└── utils.py

utils.py :

def twice(n):
return 2 * n

main.nim :

import pkg/nimpy

proc main() =
let utils = pyImport("utils")

main()

However, this drops an error:

Error: unhandled exception: <class 'ModuleNotFoundError'>: 
No module named 'utils' [Exception]

We cannot import utils.py :( The reason is the following: Python modules are looked up in a list of directories and the current folder is not present in this list!

Proof:

import pkg/nimpy

proc main() =
let
sys = pyImport("sys")
path = sys.path.to(seq[string])

for p in path:
echo p

main()

Output:

/usr/lib/python314.zip
/usr/lib/python3.14
/usr/lib/python3.14/lib-dynload
/usr/lib/python3.14/site-packages

Solution:

Add the current folder to sys.path and then utils.py will be found.

import std/os

import pkg/nimpy

proc main() =
let sys = pyImport("sys")
discard sys.path.insert(0, getAppDir()) # directory of the running binary

let
utils = pyImport("utils")
result = utils.twice(5).to(int)

echo result # 10
echo result.typeOf # int

main()