Issue with number slider or GhPython

When number slider has its minimum set to 0.0 and its value to 0.0 it is considered as None(NULL) inside GhPython instead of 0.0 (8.7 KB)

That is how python works. It is not considered None, that you do yourself on line 14 and 17.

In python 0 and 0.0 evaluate to False in a comparison or boolean check. So if not 0: will be True and go into the statement block. Hence your x gets set to None, and then your a gets set to x.

Many languages have 0 evaluate to False. You’ll find for instance C and C++ code littered with checks for values that are not 0, nullptr etc.

ok, how can I check if variable has a value?

Explicitly check against None:

if a==None:

From py2.7 interpreter:

>>> if 0 == None: print("hi")
1 Like

I always wondered how different is not and != are

Nitpick, but you didn’t use is not, but not.

You could do:

if a is None:
  x = None

or the invers

if a is not None:
  x = 42
  x = None
if not x:
# is different from
if x is not None:
# this is even more confusing

Riddle me this then.

If I use if not x: and the minimum of the slider is not 0, then at value 0 x is not considered as None.

My bad, it is considered as None.

You must understand that None is a type. 0 is a value of type integer (0.0 a float (or double).

Using is you compare types, so if something is put into your a it will have a type other than None.

Using just the if not a: you get a boolean check where a can be of many types, but still evaluate to True or False.

To False evaluate at least the values 0, 0.0, "", [], {} - you may see a pattern here. Typically a zero value of a type will evaluate to False, any non-zero value evaluates to True.

Perhaps now you can see why your initial code failed for the 0.0case by giving unexpected execution.

1 Like

That’s a very good explanation.
Thanks Nathan.

By the way, this explanation fixed a lot of scripts I could not figure out why they are not working properly. :slight_smile: