Python exception handling: Check return value of function

Question

Before using the value of a return of a function, I want to check if the value is useable. So what I have is more or less the following:

def get_module():
  import foo
  return foo

def do_something():
  try:
    module = get_module()
  except:
    print "error"

  module.bar()

Unfortunately, it seems to me that this never raises an exception. In particular, I want to check (a) that the module was transferred correctly and (b) that the module is one of three possible modules.

I know I can check through if-statements, but I feel that exception handing is ought to be the correct way.

it never raises an exception... if foo doesn't exist. Otherwise get_module will raise ImportError (which you should catch explicitly instead of a bare except) — roippi
– roippi, Commented Mar 17, 2014 at 17:52

alecxe · Accepted Answer · 2014-03-17 17:56:58Z

1

If foo cannot be imported, the code below will produce an ImportError exception:

def get_module():
    import foo
    return foo


def do_something():
    try:
        module = get_module()
    except ImportError:
        print "Import Error!"
        raise

    module.bar()


do_something()

Produces:

Import Error! 
Traceback (most recent call last):
    ...
import foo 
ImportError: No module named foo

Note, that you should either reraise the exception via raise in the except block, or make a return, so that you don't get an error on module.bar() line because of undefined module variable.

Hope that helps.

answered Mar 17, 2014 at 17:56

alecxe

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1 Comment

alex Over a year ago

Ah yes. I think I start to get Python's exception handling. Thank you!

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