raising an exception in python

**RingZzer0** · 12-03-2011, 04:55 AM

Hi Guys,

I am back with a doubt again:

I read that we can "raise" and exception in python if our program detects and error condition, e.g.

Code:

def get_num():number = int(raw_input('Enter number: '))
if number < 0:raise ValueError, ' %s is not a positive number' % number
return number

Now my question is - are we bound to use built-in exceptions only for the "exception type"?
The answer seems 'yes' to me. Could someone throw light on this topic please?

**mayjune** · 01-16-2012, 02:22 AM

Old post, but the answer is no. You can throw any exception, Program has no way of knowing it.
An example,

Code:

if 123 == 12:
    pass
else:
    raise ValueError

It outputs:-

Code:

Traceback (most recent call last):
  File "<pyshell#73>", line 4, in <module>
    raise ValueError
ValueError

Correct me, if I am wrong

**RingZzer0** · 01-18-2012, 05:06 AM

Thanks for responding mayjune though it seems you did not get my question -

Code

Code:

if 123 == 12:
    pass
else:
    raise mayjune

Output

Code:

root@bt:~/Desktop/Python# ./taste.py
Traceback (most recent call last):
  File "./taste.py", line 6, in <module>
    raise mayjune
NameError: name 'mayjune' is not defined

**neo** · 02-21-2012, 02:18 PM

Sorry for so much late reply... I had not seen this thread.

You need to create your own error class to raise custom errors
e.g.

Code:

class mayjune(Exception):
       def __init__(self, value):
           self.parameter = value
       def __str__(self):
           return repr(self.parameter)

if 123 == 12:
    pass
else:
    raise mayjune("My Error")

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