Array of Functions

Ian Kelly ian.g.kelly at gmail.com
Fri Nov 14 23:50:42 CET 2014


On Fri, Nov 14, 2014 at 3:17 PM, Richard Riehle <rriehle at itu.edu> wrote:
> In C, C++, Ada, and functional languages, I can create an array of functions, albeit with the nastiness of pointers in the C family.   For example, an array of functions where each function is an active button, or an array of functions that behave like formulae in a spreadsheet.  I am finding this a bit challenging in Python.
>
> Example:
>
>             r1c1   r1c2  r1c3
>             r2c1   r2c2  r2c3
>             r3c1   r3c2  r3c3
>
> where r1 is row 1 and c1 is column 1.  Suppose I want an array where the colum three is a set of functions that operates on the other two columns, depending on the values I set for those rows and columns?    As noted, I can do this pretty easily in most languages (well, except for Java which does not support any kind of functional programming capability), even if I have to use pointers.
>
> I think my difficulty is related to the REPL nature of Python.  However, I am sure some clever Pythonista has found a way to do this.

>>> list_of_functions = [lambda x=x: x + 4 for x in range(3)]
>>> list_of_functions[0]()
4
>>> list_of_functions[1]()
5
>>> list_of_functions[2]()
6

If you want more help, you'll have to be more specific about the
problem you're encountering. Since you didn't go into any detail, I'm
just going to assume that it's the common pitfall of variable scoping
in functions defined in a loop and point you to this FAQ answer:

https://docs.python.org/3/faq/programming.html#why-do-lambdas-defined-in-a-loop-with-different-values-all-return-the-same-result



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