Swift: Python interoperability does not work: cannot call value of non-function type 'PyValue'

[roman-kh]

Running this code:

let np = Python.import("numpy")
let a = np.arange(15).reshape(3, 5)

throws

py.swift:5:18: error: cannot call value of non-function type 'PyValue'
var a = np.arange(15).reshape(3, 5)
        ~~~~~~~~~^

While np is <module 'numpy' from '/usr/local/lib/python2.7/dist-packages/numpy/__init__.pyc'>

Bu the way, how to link Swift to Python 3?

[dan-zheng]

Currently, you have to call np.arange.call(with: 15).reshape.call(with: 3, 5).
The need to call .call(with) explicitly will go away with the Dynamic Callable proposal, but it is yet to be implemented.

[roman-kh]

Thanks very much! That helped.

How to pass named arguments then?

And what about Python 3?

[dan-zheng]

You can pass keyword arguments using the kwargs argument of PyValue.call(with:kwargs:):

import Python
let np = Python.import("numpy")
let matrix = np.ones.call(with: [2, 3], kwargs: [("dtype", np.double)])

You can find look at the python_runtime.swift test file for more Python usage examples. Notably, PyValue conforms to many ExpressibleByXXLiteral protocols, allowing you to write code like:

let dict: PyValue = [1: "hello", 2: 3.14]

Python 3 is not supported, the compiler is currently hard-coded to use Python 2.7. I filed issue #13 to address Python 3 and describe some possible solutions.

[roman-kh]

Thanks a lot!