On 01 Aug 2007 16:55:53 GMT, Stargaming <[EMAIL PROTECTED]> wrote: > On Wed, 01 Aug 2007 11:28:48 -0500, Chris Mellon wrote: > > > On 8/1/07, beginner <[EMAIL PROTECTED]> 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. > > Could you come up with an example? I can only think of accidentally > injecting a comma, what would create a (true, in a boolean context) tuple. > > And, well, if you're only using () for readabilty, this might sometimes > look messy when calling assert with the extended syntax:: > > assert(False), "error text" >
It's very easy to write this as assert(False, "error text") if you're in the habit of thinking that assert is a function. > Where one could expect the construction of a tuple. > > > 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. > > Well, the `assert` isn't there for no reason, but if you're serious about > it, `raise` could be better. > > > Thirdly: This sort of testing is precisely what unit tests and/or > > doctests are for. > > Huh? What beginner is doing there seems more like input validation than > testing. Unit or doctests are meant for testing (and in case of doctests, > showing) whether a function works as expected. Not in a big __debug__ block it isn't. > -- > http://mail.python.org/mailman/listinfo/python-list > -- http://mail.python.org/mailman/listinfo/python-list
