bruno at modulix wrote: > Yves Glodt wrote: >> Hello, >> >> if I do this: >> >> for row in sqlsth: >> ________pkcolumns.append(row[0].strip()) >> ________etc >> >> >> without a prior: >> >> pkcolumns = []; >> >> >> I get this error on first iteration: >> UnboundLocalError: local variable 'pkcolums' referenced before assignment >> >> >> I guess that's normal as it's the way python works...?!? > > yes sir. > >> My question is: Is there no way to append to a non existing list? > > No. Definitively. And that's a Good Thing(tm). > > How would you use something that doesn't exist ??? > >> I am lazy for declaring it first, > > s/declaring/instantiating/ > > If you were to use your own class Toto, would you ever hope that the > following code would work : > > for v in some_seq: > toto.dothis(v) > > without instantiating Toto and binding it to the name 'toto' before ? > Well, in Python, a list is an instance of class list. There are > syntactic sugar to instanciate a list (or a tuple or a string or a dict > etc), but this: > > my_list = [] > > is strictly equivalent to this: > > my_list = list() > > Now let's try something else: > > class Machin(object): > def append(self, value): pass > > class Bidule(object): > def append(self, value): pass > > for i in range(10): > m.append(i) > > > How should Python interpret this ? Should it create a list, or a Machin, > or a Bidule, or an instance of whatever imported class having a > append() method ?
ok I see your point, and python's... (just FYI, and not to start a flamewar ;-): In php, the [] means "append to an array object". If the array does not exist yet, it's created. [] *is* explicit for arrays, thus for php it's clear what you want.) >> IMHO it bloats the code, > > run your python interpreter and type: > import this > > Then read carefully. > > Now if being explicit still hurts your personal convictions, there's > this other language with a name starting with p... !-) no thanks, this is the 21st century ;-) >> and (don't >> know if it's good to say that here) where I come from (php) I was used >> to not-needing it... > > Not creating an Array before using it is Bad Style in PHP (and generate > a Warning BTW). an "undefined" notice, yes, not a warning... ;-) > There are warts in Python (as in any other languages), and there are > things that sometimes bore me but are not really warts. But having to > explicitely instanciate objects can't be seen as a wart in any language > IMHO !-) Ok... I thank you for all the explanations. It helps me to see more far. I (and will continue to) use php for web, and wanna standardize on python for all non-web stuff we are doing, so I might be a frequent guest on this list... have a nice day, Yves -- http://mail.python.org/mailman/listinfo/python-list
