On Wed, Mar 15, 2017, 5:12 AM likage <[email protected]> wrote:
> Try wrapping it in a lambda?
> self.btn_add = cmds.symbolButton( width=60, height=20, annotation='Add
> object(s)', image='add.xpm', command=lambda *x: self.add_btn_callback(
> "item_list") )
>
>
> Okay, so it works. And my question is why?
>
Python has a concept called "first class functions". It means a function is
an object just like anything else, like strings and lists. They can be
passed around as args and saved as references in variables. Callbacks are
implemented by have a function passed as an object so that the function can
be saved and called later.
def hello():
print "hello"
# call function immediately
hello()
# assign function to variable
fn = hello
fn()
Note that if you don't return a value from a function, the return value is
implicitly None. This will explain strange errors about the type when you
call the function instead of passing it as a first class function.
val = hello()
print type(val)
For more information here is a tutorial and a general wiki:
https://newcircle.com/bookshelf/python_fundamentals_tutorial/functional_programming
https://en.m.wikipedia.org/wiki/First-class_function
Justin
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