2013-12-06 Extend the exception stack in Python
Most of the time, message given by exception are not enough precise to quickly understand the error. To add more information, I used to catch it and throw a new one:
try :
# something
except Exception as e :
message = "my message with more information \n" + str(e)
raise Exception(message)
However, it is possible to do this:
try :
# something
except Exception as e :
message = "my message with more information"
raise Exception(message) from e
It does not break the exception stack as before. The new exception is just added to it.
In the following example, I added a message which shows the content of variable x and y.
x,y = 5,3
try :
z = 1 / (y**2 -2*y + 1 - (y-1)**2)
except Exception as e :
message = "computation error with number x={0}, y={1}".format(x,y)
raise Exception(message) from e
The exception stack is:
Traceback (most recent call last):
File "y.py", line 3, in <module>
z = 1 / (y**2 -2*y + 1 - (y-1)**2)
ZeroDivisionError: division by zero
The above exception was the direct cause of the following exception:
Traceback (most recent call last):
File "y.py", line 6, in <module>
raise Exception(message) from e
Exception: computation error with number x=5, y=3
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Xavier Dupré
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