syntax questions

[Michael Chermside]

> I know about the dir() function,  but I'm surprised that my list object
> hides a function object (even if they have the same name). 
> Is that how python treats names all the time? Does it mean you can't
> have a class, def and variable of the same name?

Yes, that's how it works all the time.

Actually, the ADVANTAGE of this is that you aren't required to memorize 
the entire list of all built-in functions and things. For instance, if 
you NEVER, EVER use the "input" function (as well you shouldn't), then 
it's not going to hurt you if you use a line like:

     for input in sys.stdin:
         process(input)

Of course, it's still not a good idea, but you aren't forced to memorize 
the list of built-in stuff, nor does old code break when a new built-in 
function is added (which happens rarely, but does happen).

As for having a class, a "def" (ie, function), and a variable all with 
the same name, no... not in the same namespace. And this is good. 
Because in Python (unlike some languages), a function, a class, and a 
"variable", are all objects, and can be used interchangably.

Consider the map() function. It is normally passed a function as its 
first argument and applies it to the items in a list:

     >>> def add5(x):
	    return x + 5
     >>> map( add5, range(4) )
     [5, 6, 7, 8]

But classes are instantiated by calling them, as if they were functions. 
So we can pass a class in, where it expects a function, and it all works 
just fine:

     >>> from UserString import UserString
     >>> map( UserString, range(4) )
     ['0', '1', '2', '3']

We could even use a variable to store the item to pass... resulting in 
code like this:

     >>> f1 = add5
     >>> f2 = UserString
     >>> [ map(f, range(4)) for f in f1, f2]
     [[5, 6, 7, 8], ['0', '1', '2', '3']]

So the fact that all things are just "objects" and don't have separate 
namespaces is highly useful, since it comes closer to making 
"everything" first class objects, giving the language more power.

-- Michael Chermside