如何捕获python ImportError作为Shell错误

Question

I have a following script which checks whether a python module is installed or not.

{

ipython -c 'from package import module' && echo "Successful import"

} || echo "package not found!"

This is a typlical try..catch syntax of bash. If the command before && would work it will execute the command after that otherwise execute the command after ||.

But in this case, whether package is installed or not, or should I say whether the command

ipython -c 'from package import module'

returns None or ImportError , bash reads it as successful execution and prints "Successful import"

How can I check for a successful import of a python package using bash?

EDIT : And return with exit status 1?

Answer 1

You can use the exception SystemExit(msg=None) with any message that's not None or 0 . If it's uncaught, it'll cause the program to end, and if the msg is not None or 0 , with an exit code of 1 . (see: https://docs.python.org/3/library/exceptions.html#SystemExit ).

test.py

try:
    import Blue
except ImportError:
    raise SystemExit("Import Error!")

in bash:

[user]@[host] $ python test.py 
Import Error!

[user]@[host] $ python test.py || echo "blarg"
Import Error!
blarg

[user]@[host] $ python test.py && echo "blarg"
Import Error!

Answer 2

Use the python command for running code snippets programmatically, instead of ipython .

There's an outstanding bug about this: https://github.com/ipython/ipython/issues/6912

Answer 3

You have at least two possibilities:

• Using "pip" on your shell script to get the list of installed packages then grep for tour package:

  pip list | grep yourpackage && echo installed || echo "NOT Installed"

• Using Python-bash script, I don't know exactly how to call it but I know how to use it:

Something like:

output=$(
python - <<EOF
try:
    import your_package;
    print "Package Installed"
except Exception:
    print "Package not installed"
EOF
)

echo $output

here you have alot of alternatives to check for the existence of the package/module, so, intead of trying to import the package, you can check it's existence in a pythonic way. You can grab the different solutions for this answer or this and replace the import your_package; with one of them.