Issue using Python.import_module to import python numpy package in Mojo

Question

I've just started learning Mojo, following the documentation to get started. I've run into a problem with importing the Python module numpy. Below is the code I am using which is taken from the documentation.

from python import Python

fn use_array() raises:
   # This is equivalent to Python's `import numpy as np`
   let np = Python.import_module("numpy")

   # Now use numpy as if writing in Python
   let array = np.array([1, 2, 3])
   print(array)

use_array()

After running this I then receive the following error:

mojo: error: failed to parse the provided Mojo

If I put a try/except statement around the let np = Python.import_module("numpy") it runs, gives the same error with the additional error of:

error: use of unknown declaration 'np',
'fn' declarations require explicit variable declarations
     let array = np.array([1, 2, 3])

I also get this same error when trying to create functions using def() rather than fn(). Finally, I attempted to put use_array() in the fn main() function but to no avail either.

Rather new to this language, but very familiar with Python so if anyone can help it would be greatly appreciated!

M

Answer 1

to run mojo code locally make sure, for current language stage at least, that you have latest version:

# in case if you on Mac
brew update
brew update modular
modular upgrade mojo

to use python packages:

# make sure this packages installed in your py venv
# or in any other way you manages your virtual environment and packages
python3 -m venv .venv
source .venv/bin/activate

for the code it self, as you noticed you must have main function:

code:

from python import Python

def use_array():
   let np = Python.import_module("numpy")
   let array = np.array([1, 2, 3])
   print(array)

def main():
    use_array()

output:

(.venv)pip install numpy
(.venv)mojo run w.mojo
(.venv)mojo run w.mojo
[1 2 3]