At 01:34 PM 7/12/2008, Kent Johnson wrote:
On Sat, Jul 12, 2008 at 4:01 PM, Dick Moores <[EMAIL PROTECTED]> wrote:
> _Python in a NutShell_, p. 138 has a bit on the assert statement which I
> don't completely understand.
>
> It says the syntax is
>
> assert condition[, expression]
>
> I was hoping to put some sort of explanation of failure in an assert
> statement. But how to do it?
>
> In my code I have
>
> assert(len(list(set(colors_used_this_cycle))) ==
> len(colors_used_this_cycle), "A color has been used twice!")
Leave out the outermost parentheses, assert is a statement, not a
function call.
Ah. OK.
In [2]: assert(False, "Asserted false")
This is "assert condition" where the condition is a tuple with two
elements, hence true so there is no output.
In [13]: assert(3 < 2 , "qwerty")
In [14]:
I don't understand that logic. Could you unpack it for me?
In [3]: assert False, "Asserted false"
---------------------------------------------------------------------------
<type 'exceptions.AssertionError'> Traceback (most recent call last)
/Users/kent/<ipython console> in <module>()
<type 'exceptions.AssertionError'>: Asserted false
This is the form with an optional expression and works the way you want.
In [14]: assert 3 < 2, "Bad math"
---------------------------------------------------------------------------
AssertionError Traceback (most recent call last)
E:\Python25\Scripts\<ipython console> in <module>()
AssertionError: Bad math
In [15]:
Yes.
Thanks, Kent.
Dick
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