Creating custom exception types

Create a class inheriting from Exception:

class FooException(Exception):
    pass
try:
    raise FooException("insert description here")
except FooException:
    print("A FooException was raised.")

or another exception type:

class NegativeError(ValueError):
      pass

def foo(x):
    # function that only accepts positive values of x
    if x < 0:
        raise NegativeError("Cannot process negative numbers")
    ...  # rest of function body
try:
    result = foo(int(input("Enter a positive integer: ")))  # raw_input in Python 2.x
except NegativeError:
    print("You entered a negative number!")
else:
    print("The result was " + str(result))

Found a mistake? Have a question or improvement idea? Let me know.

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