Assertion in list comprehension

[beginner]

On Aug 1, 11:28 am, "Chris Mellon" <arka... at gmail.com> wrote:
> On 8/1/07, beginner <zyzhu2... at gmail.com> wrote:
>
>
>
>
>
> > Hi,
>
> > Does anyone know how to put an assertion in list comprehension? I have
> > the following list comprehension, but I want to use an assertion to
> > check the contents of rec_stdl. I ended up using another loop which
> > essentially duplicates the functions of list comprehension. It just
> > look like a waste of coding and computer time to me.
>
> > I just wish I could put the assertions into list comprehensions.
>
> >         x=[(rec_stdl[0].st/10000.0,
> >             rec_stdl[0].cl,
> >             rec_stdl[0].bb,
> >             rec_stdl[0].bo,
> >             rec_stdl[1].bb,
> >             rec_stdl[1].bo,
> >             rec_stdl[0].ex
> >            )
> >            for rec_stdl in rec_by_ex if len(rec_stdl)==2
> >         ]
>
> >         #duplicated loop
> >         if __debug__:
> >             for rec_stdl in rec_by_ex:
> >                 l=len(rec_stdl)
> >                 assert(l<=2 and l>0)
> >                 if l==2:
> >                     assert(rec_stdl[0].c=="C" and rec_stdl[1].c=="P")
> >                     assert(rec_stdl[0].ex==rec_stdl[1].ex)
> >                     assert(rec_stdl[0].st==rec_stdl[1].st)
> >                     assert(rec_stdl[0].cp==rec_stdl[1].cp)
>
> First: All your asserts are wrong. Assert is a statement, not a
> function. These specific ones will behave as expected, but it's easy
> to accidentally write ones that always pass this way.


Do you mean I should not use the parentheses?


> Secondly: This is a waste of code, because if __debug__ is not defined
> asserts will be skipped by the compiler. You could use the same loop
> block for both branches.

I know. My original question was how. Dan suggested to write a checker
function.


> Thirdly: This sort of testing is precisely what unit tests and/or
> doctests are for.

Agreed.