The big difference I have seen is that with npm I have never run into issues because the code is being executed with the incorrect version of the interpreter, or something weird like python being installed at an unexpected path.

Also npm is just one tool which behaves consistently and takes full responsibility of making a project portable. With Python it seems as if it's at the whim of the developer to choose from a variety of tools to complete this task.

In other words, if I see `pacakage.json` in my project directory, I know it will tell me everything I need to know to run the project. With Python, if the previous developer hasn't documented what tools they were using, I might have to do some archeology to understand how they have encapsulated the project's dependencies.

Or worse, if they never encapsulated their project's dependencies, I might just have to guess how the environment was set up on their workstation and try to recreate it through trial and error.