Python: Catching specific exception
in except ValueError,e
, e
is an instance of the exception, not a string. So when you test if e
is not equal to a particular string, that test is always False. Try:
if str(e) != "..."
instead.
Example:
def catch(msg):
try:
raise ValueError(msg)
except ValueError as e: # as e syntax added in ~python2.5
if str(e) != "foo":
raise
else:
print("caught!")
catch("foo")
catch("bar")
Typically, you don't really want to rely on the error message if you can help it -- It's a little too fragile. If you have control over the callable macdat
, instead of raising a ValueError
in macdat
, you could raise a custom exception which inherits from ValueError
:
class MyValueError(ValueError): pass
Then you can only catch MyValueError
and let other ValueError
s continue on their way to be caught by something else (or not). Simple except ValueError
will still catch this type of exception as well so it should behave the same in other code which might also be catching ValueErrors from this function.
The method for the last one is correct (but print repr(e) to see why it doesn't work).
However, if you want the exception information to be correct, you should not raise a new exception (as you do now), but raise the same one. Otherwise more code catching it, or the error message if it isn't caught, will show your code as the source, while it should be the original source.
To do this, use raise without an argument (within the except block, of course, otherwise there is no "current" exception).
You can use: type(e)
and e.args
for this. It returns a tuple, match the tuple with your own.