Improve Python (.exe) startup time

Question

I created an exe with the PyInstaller. As soon as I enable the --onefile flag. The exe needs several minutes to start. When I build the application with the --onedir flag, the exe launches immediately after launch. In order to distribute the application better, it is important for me that the exe is created with the --onefile flag.

My problem can be reproduced with the following two scripts.

In main.py I only import the torch module, because the problems only occur with this module.

#main.py
print("Test1")
import torch
print("Test2")
print(torch.cuda.is_available())
print("Test3")

I generate the exe with the setup.py file.

#setup.py
import PyInstaller.__main__
import pyinstaller_versionfile

PyInstaller.__main__.run([
    'main.py',
    '--onefile',
    '--name=Object Detection',
    '--console',
])

Alternatively, the exe can also be generated using the Powershell command.

pyinstaller --noconfirm --onefile --console --name "Object Detection"

So my question is what can be done to make the application start faster? What is the specific cause of the problem?

By excluding the module --exclude-module=torch the application also starts immediately, but that's not my goal.

Answer 1

Pyinstaller --onefile mode has to unpack all libraries before starting in a temporary directory, when you use --onedir they are already there. The problem is noticeable with big libraries like PyTorch ...