[portland] Dictionary As Switch Statement

kirby urner kirby.urner at gmail.com
Fri Jan 18 02:41:31 CET 2008

> I use 'self' because I thought that the function calls needed the trailing
> parentheses to identify them as functions. When I did this, python told me
> it was expecting 1 argument for each function and I supplied 0 arguments. So
> I added 'self' and the incorrect argument number error went away.
> Thank you,
> Rich

Actually, they don't require the parentheses except to trigger them
as "callables" (a Pythonic jargon word, "iterables" being another
favorite -- dictionaries and lists are both iterables, as are generator

So for example, you can go:

def f(x):  return x * x  # arbitrary function, takes x

def g(x): return x + 2  # another function


myfuncs = {'square it' : f, 'add 2' : g}  # a dictionary, no parentheses

Then if the user chooses "square it" for some
reason you can go:

x = 10
myfuncs["square it"](x)

where x is getting its value from somewhere in scope.

Note that myfuncs["square it"] is merely returning the
function object f, whereas the parentheses and argument
are here being supplied at runtime.


> --
> Richard B. Shepard, Ph.D.               |  Integrity            Credibility
> Applied Ecosystem Services, Inc.        |            Innovation
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