Python - 检查缺失库依赖项的用户友好方式的最佳实践？

Question

Let's say my Python 3.6 script requires bar in the library foo , which it import s at the beginning:

from foo import bar

What I'd like to do is for the script to attempt the import , and give feedback to a downstream user if foo is not available on their system and that they should install it.

So far, I've managed to hack together this solution which is probably not very good:

try:
    from foo import bar
except:
    print("Need `foo` library installed")
    exit(1)

I used print() because I hope this can be a direct message to the user, but not sure if that's a good idea in the context of exception handling?

Also, there are at least two more problems here:

1. The except clause would apply to any error that happens during import including cases where the error is something other than the absence of foo . So this probably isn't a good use of exception handling?
2. My script import s multiple libraries, and I have to create a chunk like the above for each one!

I briefly considered creating a for loop that goes through a list of library dependencies and import each one. Eg:

list_of_libraries: list = ["foo", "lorem", "ipsum"]
for library in list_of_libraries:
    try:
        import library
    except:
        print("Need " + library + " library installed")
        exit(1)

However, this also looks bad to me because:

• Each loop iteration import s the whole library
• It would fail because I don't think import takes a string ?
• It doesn't really solve problem 1 above.

Am I stupidly missing something here? What's a good way to implement this? Thank you.

EDIT: There are existing answers such as this one which discusses how to list dependencies in requirements.txt and installing them with pip . However, my question is focused on solutions I can implement inside my Python script to catch missing libraries and prompting the user to install them .

Answer 1

Exception Clause

You can catch ModuleNotFoundError (exists as of Python 3.6) or ImportError (for all Python versions) to restrict your except clause to cases of import troubles. ModuleNotFoundError is a subclass of ImportError , so catching ImportError will work in all versions of Python.

Error Output

Errors in standard linux applications would be written to stderr instead of stdout. So instead of using plain print , you would do as follows:

import sys

try:
    from foo import bar
except ImportError:
    print("Need `foo` library installed", file=sys.stderr)
    exit(1)

You can test it by redirecting stdout to /dev/null . You will still see the error message:

$ python foobar.py >> /dev/null
Need `foo` library installed

Better Handling Possible?

As for a better method than writing each import individually or looping over the required libraries, I unfortunately do not know. I have seen the try except ImportError pattern been used for compatibility between modules that were renamed from Python 2 to Python 3. So for individual libraries it seems to be normal, but I have not seen anybody mass check imports.