Python: How to get exception as an object from a string with the same name?

Question

Imagine I have strings containing names of exceptions:

s1 = 'KeyError'
s2 = 'ArithmeticError'
s3 = 'OSError'
s4 = 'ZeroDivisionError'
.....
sn = 'SomeOtherError'

What I need to do is:

if issubclass(s4, (s1, s2, s3, sn)) == True:
print('You dont have to catch this exception because the parent is already caught')

Using globals() doesn't help in this case for some reason. Since I am not an experienced programmer, I can only guess that it's because those are built-in exceptions...

Nevertheless, what can be done to accomplish what I try to accomplish?

Any suggestions would be appreciated!

Answer 1

The most reliable way is probably to search the class hierarchy. All built-in exceptions are ultimately descendants of BaseException, so just search its children recursively:

def find_child_class(base, name):
  if base.__name__ == name:
    return base

  for c in base.__subclasses__():
    result = find_child_class(c, name)
    if result:
      return result

>>> find_child_class(BaseException, 'KeyError')
<class 'KeyError'>

This will also work for user-defined exceptions, as long as the module that defines them has been loaded and the exceptions are derived from Exception (which they should be).