Navigating Name and Import Errors

00:00 There’s a few different ways that accessing names in Python can trip you up. If you try to access a variable name that isn’t present in a given Python scope, you’ll encounter a NameError.

00:10 On the other hand, if you try to import something and it can’t be found, you’ll either get a ModuleNotFoundError or its more general parent class, the ImportError.

00:20 Let’s see some situations that can trigger these exceptions.

00:24 Open up the REPL, and a NameError is easy to generate. Try to access a variable name that doesn’t exist like bob. Indeed. NameError: name ‘bob’ is not defined`.

00:37 A more realistic example would be accessing a library that does exist that maybe you forgot to import, like trying to grab the path attribute of the sys module. sys.path, and a much more helpful error this time. NameError: name ‘sys’ is not defined`.

00:53 Did you forget to import 'sys'? The ModuleNotFoundError occurs when you ask Python to import a module and it can’t be found. This happens most commonly when you’ve forgotten to install the module prior to running the code.

01:06 Or perhaps you’ve misspelled the module’s name. Try to import a non-existing module named non_existing. ModuleNotFoundError: No module named ‘non_existing’.

01:18 Now this error only covers the cases where the module you’re importing or importing from can’t be found. All other cases of failed imports fall under the more general ImportError.

01:28 An important distinction for you to consider, especially when it comes to handling these exceptions using try except. To see an ImportError, you can try importing something that doesn’t exist from within a module that does.

01:41 from sys import non_existing

01:44 and there’s the different ImportError: cannot import name 'nonexisting' from 'sys' (unknown location). For a practical example, you can use ModuleNotFoundError to identify what a module is missing and dynamically load a different module at runtime.

02:00 If your program needs to parse a TOML file, for instance, you could use the built-in tomllib module in any version of Python since 3.11. But if you try to import tomllib and get a ModuleNotFoundError, you can use try and except to instead import the third-party library tomli, which would, of course, need to be installed as a dependency.

02:20 You could do something like this: try: import tomllib

02:28 except ModuleNotFoundError:

02:33 import tomli as tomllib.

02:37 Either way, you end up with a TOML parsing library assigned to the variable named tomllib. Of course, this only works if the two libraries have more or less the same API, but you get the general idea of what you can do with this.

02:51 And if these examples have made you a little more curious about how imports work generally, head on over to advanced Python import techniques for a deep dive.

03:00 It’s import-ant info for sure, and if you’re still with me after that pun, I’ll see you in the next lesson where you’ll look into lookup-related exceptions.