Nim - Python bridge


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Native language integration with Python has never been easier!

Implementing python module in nim

# mymodule.nim - file name should match the module name you're going to import from python
import nimpy

proc greet(name: string): string {.exportpy.} =
    return "Hello, " & name & "!"
# Compile on Windows:
nim c --app:lib --out:mymodule.pyd mymodule
# Compile on everything else:
nim c --app:lib mymodule
import mymodule
assert(mymodule.greet("world") == "Hello, world!")

Calling python from nim

import nimpy
let os = pyImport("os")
echo "Current dir is: ", os.getcwd().to(string)

# sum(range(1, 5))
let py = pyBuiltinsModule()
let s = py.sum(py.range(0, 5)).to(int)
assert(s == 10)


The library is designed with ABI compatibility in mind. That is the compiled module doesn't depend on particular Python version, it should properly work with any. The C API symbols are loaded in runtime from whichever process has launched your module.

Troubleshooting, Q&A


Importing the compiled module from Python fails with ImportError: dynamic module does not define module export function ...

Make sure that the module you're importing from Python has exactly the same name as the nim file which the module is implemented in.


Nim strings are converted to Python bytes instead of string

nimpy converts Nim strings to Python strings usually, but since Nim strings are encoding agnostic and may contain invalid utf8 sequences, nimpy will fallback to Python bytes in such cases.


Is there any numpy compatibility?

nimpy allows manipulating numpy objects just how you would do it in Python, however it not much more efficient. To get the maximum performance nimpy exposes Buffer protocol, see raw_buffers.nim. tpyfromnim.nim contains a very basic test for this (grep numpy). Higher level API might be considered in the future, PRs are welcome.

Future directions

  • exporting Nim types/functions as Python classes/methods
  • High level buffer API
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License: MIT

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