multiarray failed to import error

Problem

I installed PyTorch locally using pip3. And then I wrote my first PyTorch program that had this import at the top: import torch.nn as nn.

When I ran the script, that import failed with this error:

Traceback (most recent call last):
  File "./tmp.py", line 3, in <module>
    import torch.nn as nn
  File "/home/ashwin/.local/lib/python3.6/site-packages/torch/__init__.py", line 79, in <module>
    from torch._C import *
ImportError: numpy.core.multiarray failed to import

Solution

I have faced this problem many times in different environments. It has always been due to clashes between multiple NumPy libraries installed on the system.

Here are the solutions that worked for me:

• Uninstall the NumPy installed by pip3 and keep the Ubuntu package.
• Uninstall the Ubuntu NumPy package and keep the pip3 package.
• Another time, neither solution worked. I found that pip3 uninstall numpy had not removed NumPy. I went into ~/.local/lib/python3.6/ and manually deleted all NumPy related directories and reinstalled NumPy using pip3.