codon/docs/interop/python.md

Calling Python from Codon is possible in two ways:

• from python import allows importing and calling Python functions from existing Python modules.
• @python allows writing Python code directly in Codon.

In order to use these features, the CODON_PYTHON environment variable must be set to the appropriate Python shared library:

export CODON_PYTHON=/path/to/libpython.X.Y.so

For example, with a brew-installed Python 3.9 on macOS, this might be

/usr/local/opt/python@3.9/Frameworks/Python.framework/Versions/3.9/lib/libpython3.9.dylib

Note that only Python versions 3.6 and later are supported.

from python import

Let's say we have a Python function defined in mymodule.py:

def multiply(a, b):
    return a * b

We can call this function in Codon using from python import and indicating the appropriate call and return types:

from python import mymodule.multiply(int, int) -> int
print(multiply(3, 4))  # 12

(Be sure the PYTHONPATH environment variable includes the path of mymodule.py!)

@python

Codon programs can contain functions that will be executed by Python via pydef:

@python
def multiply(a: int, b: int) -> int:
    return a * b

print(multiply(3, 4))  # 12

This makes calling Python modules like NumPy very easy:

@python
def myrange(n: int) -> List[int]:
    from numpy import arange
    return list(arange(n))

print(myrange(5))  # [0, 1, 2, 3, 4]