Python handling multiple exceptions

Question

I want to handle a specific exception in a certain way, and generically log all the others. This is what I have:

class MyCustomException(Exception): pass


try:
    something()
except MyCustomException:
    something_custom()
except Exception as e:
    #all others
    logging.error("{}".format(e))

The problem is that even MyCustomException will be logged because it inherits from Exception. What can I do to avoid that?

Solution 1

What else is going on in your code?

MyCustomException should be checked and handled before flow ever gets to the second except clause

In [1]: def test():
   ...:     try:
   ...:         raise ValueError()
   ...:     except ValueError:
   ...:         print('valueerror')
   ...:     except Exception:
   ...:         print('exception')
   ...:         

In [2]: test()
valueerror

In [3]: issubclass(ValueError,Exception)
Out[3]: True

Solution 2

Only the first matching except block will be executed:

class X(Exception): pass

try:
    raise X
except X:
    print 1
except Exception:
    print 2

only prints 1.

Even if you raise an exception in an except block, it won't be caught by the other except blocks:

class X(Exception): pass

try:
    raise X
except X:
    print 1
    0/0
except Exception:
    print 2

prints 1 and raises ZeroDivisionError: integer division or modulo by zero