How to change the message in a Python AssertionError?

assert expression, info

For instance,

>>> assert False, "Oopsie"
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AssertionError: Oopsie

From the docs:

Assert statements are a convenient way
to insert debugging assertions into a
program:

assert_stmt ::=  "assert" expression
["," expression] 

The simple form,
assert expression, is equivalent to

if __debug__:
    if not expression:
        raise AssertionError 

The extended form

assert expression1, expression2

is equivalent to

if __debug__:
    if not expression1:
        raise AssertionError(expression2)

These equivalences assume that
__debug__ and AssertionError refer to the built-in variables with those
names. In the current implementation,
the built-in variable __debug__ is
True under normal circumstances, False
when optimization is requested
(command line option -O). The current
code generator emits no code for an
assert statement when optimization is
requested at compile time. Note that
it is unnecessary to include the
source code for the expression that
failed in the error message; it will
be displayed as part of the stack
trace.