I don't believe you can use the test for a __iter__ attribute in this case, for the following reason: >>> c1 = 'abc' >>> c2 = ['de', 'fgh', 'ijkl'] >>> hasattr(c1, '__iter__') False >>> hasattr(c2, '__iter__') True >>> for i in c1: print "i=%s is an element of c1" % repr(i) ... i='a' is an element of c1 i='b' is an element of c1 i='c' is an element of c1
In other words, even though the c1 single string variable does not have an __iter__ attribute, it can still be used in a for loop. I think the right answer would depend on what exactly the OP intends to do with the argument when it is a list (or is list-like in some way) -- i.e. he didn't say specifically that he wanted use it in a for loop. -Martin ==================== Terry Hancock wrote: > On Wednesday 16 February 2005 09:08 am, alex wrote: > > how can I check if a variable is a structure (i.e. a list)? For my > > special problem the variable is either a character string OR a list of > > character strings line ['word1', 'word2',...] > > > > So how can I test if a variable 'a' is either a single character string > > or a list? > > The literally correct but actually wrong answer is: > > if type(a) == type([]): > print "'a' is a duck" > > But you probably shouldn't do that. You should probably just test to > see if the object is iterable --- does it have an __iter__ method? > > Which might look like this: > > if hasattr(a, '__iter__'): > print "'a' quacks like a duck" > > That way your function will also work if a happens to be a tuple, > a dictionary, or a user-defined class instance which is happens to > be iterable. > > Being "iterable" means that code like: > > for i in a: > print "i=%s is an element of a" % repr(i) > > works. Which is probably why you wanted to know, right? > > Cheers, > Terry > > -- > -- > Terry Hancock ( hancock at anansispaceworks.com ) > Anansi Spaceworks http://www.anansispaceworks.com -- http://mail.python.org/mailman/listinfo/python-list
