difference between class statement and def statement (WAS Re: End of file)

[Steven Bethard]

Andrew Durdin <adurdin <at> gmail.com> writes:

> Another [sort-of related] question: why does the following not produce
> a NameError for "foo"?
> 
> def foo(): print foo
> foo()

I'm thinking this was meant to be "left as an exercise to the reader" ;), but 
just in case it wasn't, you've exactly illustrated the difference between a 
class definition statement and a function definition statement.  Executing a 
class definition statement executes the class block, while executing a 
function definition statement only initializes the function object, without 
actually executing the code in the function's block.  Hence:

>>> class C(object):
...     print C
...
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
  File "<stdin>", line 2, in C
NameError: name 'C' is not defined

The name of a class is bound to the class object at the end of the execution 
of a class statment.  Since executing a class statement executes the code in 
the class's block, this example references C before it has been bound to the 
class object, hence the NameError.

>>> def f():
...     print f
...
>>> f()
<function f at 0x009D6670>

The name of a function is bound to the function object when the def statement 
is executed.  However, the function's code block is not executed until f is 
called, at which point the name f has already been bound to the function 
object and is thus available from the globals.

Steve