Python error no module named torch solution

When using PyTorch in Python, I often encounter the error of no module named torch. This article summarizes the main reasons for this error and the corresponding solutions.

Reason 1: PyTorch is not installed 

To call PyTorch in Python, you must first install it. Can be run in terminal:

pip install torch torchvision torchaudio

to install PyTorch and related libraries.

Reason 2: PyTorch version is wrong  

This error can also occur if an older version of PyTorch is installed, but a newer version of the API is required in the code. The solution is to upgrade PyTorch to the latest version.

Reason 3: The environment variable is not set properly 

Sometimes although PyTorch is installed successfully, the environment variables are not set correctly and Python doesn't know how to find PyTorch. You can reactivate the virtual environment, or manually add the PyTorch installation path to ENV PYTHONPATH.

Reason 4: The environment where PyTorch is not used 

If the system has multiple Python environments, and PyTorch is only installed in one environment, and you are not using that environment to run the code, this error will also be reported. The solutions are:
- Run the code after activating the environment where PyTorch is located
- Install PyTorch in the current environment 
- Install PyTorch as a global environment

Reason 5: Forget to import torch 

This reason is embarrassing. If you forget to add the import torch import statement directly at the beginning of the Python code, a no module named 'torch' error will be reported.