How to use raise keyword in Python

Question

I have read the official definition of "raise", but I still don't quite understand what it does.

In simplest terms, what is "raise"?

Example usage would help.

Answer 1

You can use it to raise errors as part of error-checking:

if (a < b):

raise ValueError()

Or handle some errors, and then pass them on as part of error-handling:

Try:

f = open('file.txt', 'r')

except IOError:

# do some processing here

# and then pass the error on

raise