Call a function with arguments within a list / dictionary

Question

I have this code, which calls a function based on your input key. For example, if you chose pf, it would call the pf function, my_function(20).

My problem is, I know how to call a function without arguments, but I don't know how to do it with arguments. It runs all the functions right now because of the (), but how do I give it argmuents and still call it? Would I have to create a seperate list of arguments?

function_map = {
'pf':['finds the prime factors of a number',my_function(20)]
'cs':['solves a quadratic by completing the square',m.complete_square()]
'sr':['simplifies a radical',m.simplfy_radical(input('> '))]
}

for d in function_map.keys():
  print('{} - {}'.format(d,function_map[d][0])
selection = input('Input keycode >>> ')
if selection in function_map.keys():
  function_map[selection][1]()

so you want to get the arguments also from input? could you not, instead of putting the function call into your dict, just pass the function and call it once you know the arguments? — j-i-l
– j-i-l, Commented Feb 18, 2017 at 0:45
Possible duplicate of Passing functions with arguments to another function in Python? — TemporalWolf
– TemporalWolf, Commented Feb 18, 2017 at 0:47

Sebastian Wozny · Accepted Answer · 2017-02-18 01:03:59Z

4

You want functools.partial. partial is so awesome that I literally have the documentation in my bookmarks.

partial is a function that returns a function, but with some of the arguments already set:

Script

from functools import partial


def myfunc(x, y):
    print(x + y)

my_ready_func = partial(myfunc, 3)
my_ready_func(5)
my_ready_func(0)
my_ready_func(10)

Output

8
3
13

If you need to defer the execution of the input function until the actual execution of your function then this will not work as expected.

you might want to write a function that makes your function 'inputtable':

def inputtable(func,query="Whats the argument?"):
    arg = input(query)
    return func(arg)

Then you can store the inputtable function instead of your original one;

'aa':['does stuff', partial(inputtable, function, query=' > ')]

Alternatively you can write a so called decorator to make it inputtable:( I also have decorators in my bookmarks)

def inputtable(func):

    def wrapper():
        arg=input(' > ')
        func(arg)
    return wrapper

And then store it like this:

'aa':['does stuff', inputtable(function)]

Then you don't need to use partial.

edited Feb 18, 2017 at 1:03

answered Feb 18, 2017 at 0:45

Sebastian Wozny

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9 Comments

aghast Over a year ago

To elaborate on this answer: once you have a f = partial(my_function, 20) you can just call it as f() with no additional args. Which means you can store it in a list as lst = [ 'foo', f ] and then call it as lst[1]()

Dimitris Fasarakis Hilliard Over a year ago

and how would you make this work with input as the OP requires?

Dimitris Fasarakis Hilliard Over a year ago

Then add it to your answer, as it is it is implying that partial would also work with input which isn't the case.

lol Over a year ago

Would storing it like this work? 'aa':['does stuff',partial(function, input(' > '))]

lol Over a year ago

if I made a function like this: def ask(string): return input(string) would that work as an argument? 'aa':['does stuff', partial(myfunc, ask('your name > '))]

|

Dimitris Fasarakis Hilliard · Accepted Answer · 2017-02-18 00:57:18Z

2

An alternative is to use lambdas that won't evaluate (merely compile) their bodies until called:

function_map = {
    'pf':['finds the prime factors of a number',lambda: my_function(20)]
    'cs':['solves a quadratic by completing the square',lambda: m.complete_square()]
    'sr':['simplifies a radical',lambda: m.simplfy_radical(input('> '))]
}

edited Feb 18, 2017 at 0:57

answered Feb 18, 2017 at 0:56

Dimitris Fasarakis Hilliard

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2 Comments

lol Over a year ago

Why would you say this is better than partial.

Dimitris Fasarakis Hilliard Over a year ago

@lol I prefer partial, this is an alternative that does the trick if for some reason you're absolutely adamant that input('> ') must be provided as an argument.

TemporalWolf · Accepted Answer · 2017-02-18 00:54:24Z

0

function_map[selection][1]( *args ) is how, but you first have to remove the (20), ()... from the dict, as that calls the function and puts it's result in the dict, rather than storing the function itself: I then added an additional entry to the list which specifies the number of arguments.

function_map = {
'pf':['finds the prime factors of a number',my_function, 1]
'cs':['solves a quadratic by completing the square',m.complete_square, 0]
'sr':['simplifies a radical',m.simplfy_radical, 1]
}

for d in function_map.keys():
  print('{} - {}'.format(d,function_map[d][0])
selection = input('Input keycode >>> ')
if selection in function_map.keys():
  args = []
  for _ in function_map[selection][2]:
    args.append(input('Input arg>>> '))
  if args:
    function_map[selection][1]( *args )
  else:
    function_map[selection][1]()

edited Feb 18, 2017 at 0:54

answered Feb 18, 2017 at 0:50

TemporalWolf

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1 Comment

TemporalWolf Over a year ago

@lol so you need to determine how many args it takes. I've updated it... you may also have to change the type... but this shows you how.

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