test for None

[BartlebyScrivener]

How do you test for a function that returns nothing, and why doesn't
this work? Shouldn't X have to be either None or not?

x = None
for x in []:

.... if x is None:
.... print "X is None"
.... else:
.... print "X is not None"
....

Thanks,

rick

 

[Erik Max Francis]

How do you test for a function that returns nothing, and why doesn't
this work? Shouldn't X have to be either None or not?

x = None
for x in []:

... if x is None:
... print "X is None"
... else:
... print "X is not None"
...

No, because you're iterating over an empty list, which does nothing:

>>> for x in []: print 'hi' ....
>>>

 

[BartlebyScrivener]

I think I was trying for something like this, where the intervening for
iterates over a function that may or may not produce nothing:

x = None
for x in []:

print x
print "x is still none because nothing happened"

Thanks,

rick

 

[Ben Finney]

How do you test for a function that returns nothing,

A function returns a single value (which may be a container for other
values). By default, with no 'return' statement, it returns the None
object.

What is it you're trying to do?

and why doesn't
this work? Shouldn't X have to be either None or not?
Yes.

Assigns the name 'x' to the None object.

for x in []:

Iterates over an empty list, which results in zero iterations;
i.e. does nothing.

Have you followed the tutorial through, running and understanding each
example, to get the basics of Python covered?

<URL:http://docs.python.org/tut/>

 

[BartlebyScrivener]

Have you followed the tutorial through, running and understanding each
Could be high time to try that again. At first it was way too much, so
I've been doing Dive Into Python and some others. But I will try the
Tutorial again, at least up to classes. Then I'm sure I'll have to
return to the books.

Thanks for your patience.

rick