How do I store and then call strings and functions from the same dictionary?

Question

I've been trying to store and then call a string and/or a function inside a dictionary.

First example

def mainfunction():
    dict = {
        'x' : secondfunc,
        'y' : 'hello world'
    }
    while True :
        inpt = input('@')
        dict[inpt]()
    
def secondfunc():
    print('hi world')

mainfunction()

This works only if I input the key 'x'. If I try to input key 'y', I get this error.

TypeError: 'str' object is not callable

Also, the problem with this method is that it can't make a default answer.

Second example

def mainfunction():
    dict = {
        'x' : secondfunc,
        'y' : 'hello world'
    }
    while True:
        inpt = input('@')
        z = dict.get(inpt, 'Default text')
        print(z)
        
def secondfunc():
    print('hi world')
    
mainfunction()

This method works for key 'y', but for key 'x' it prints something to the effect of:

<function secondfunc at 0x7ab4496dc0>

I'm trying to make it so that whichever value I input, it will either print a default value, print a string, or execute a function. All depending on the key input.

Last example

The only solution I've found is that which uses if statements.

def mainfunction():
    dict = {
        'x' : secondfunc,
    }
    dict2 = {
        'y' : 'hello world'
    }
    
    while True:
        inpt = input('@')
        z = dict2.get(inpt, 'Default text')
        if inpt == 'x':
            dict[inpt]()
        else:
            print(z)
        
def secondfunc():
    print('hi world')
    
mainfunction()

This solution takes more code than I would like it to, and it also requires an if statement specific to the dictionary given, which takes more time. Is there no better way to do this?

It's exactly as the error says: strings are not a kind of thing that you call. Can you think of something that you *can* call (hint: maybe the other kind of thing currently being stored?) that could give you the desired string when it is called (hint: maybe by `return`ing it)? — Karl Knechtel, Aug 17 '22 at 04:46

mkrieger1 · Accepted Answer · 2021-07-21T19:31:08.930

Instead of a string itself, you need to store a function returning a string in the dictionary.

Most simply this can be done as an anonymous function using the lambda syntax:

answers = {
    'x': secondfunc,
    'y': lambda: 'hello world'
}

(It's bad practice to name this dictionary dict, because it shadows the built-in dict, so I'll use a better name here.)

Of course, secondfunc should not print a string, but return a string, as well, since printing is already the job of mainfunc (see also: Difference between returns and printing in python?):

def secondfunc():
    return 'hi world'

Now, print(answers['x']()) and print(answers['y']()) are working equally.

To create a default answer with the dictionary .get() method, it also needs to be a function returning a string:

def mainfunction():
    answers = {
        'x' : secondfunc,
        'y' : lambda: 'hello world'
    }
    while True:
        inpt = input('@')
        z = answers.get(inpt, lambda: 'Default text')()
        print(z)

Thank you, eliminates the need for IF statements. – Tristan Davis Jul 21 '21 at 19:28 — Tristan Davis, Jul 21 '21 at 19:28

score 0 · Answer 2 · answered Jul 21 '21 at 18:59

You can use the callable() function to test if the dictionary value is a function. If it is, call it, otherwise just print the value itself.

def mainfunction():
    dict = {
        'x' : secondfunc,
        'y' : 'hello world'
    }
    while True:
        inpt = input('@')
        z = dict.get(inpt, 'Default text')
        if callable(z):
            z()
        else:
            print(z)

score 0 · Answer 3 · answered Jul 21 '21 at 18:59

0

You can use the callable() built-in function to test if the given object is callable.

z = dict2.get(inpt, 'Default text')
if callable(z):
    z()
else:
    print(z)

answered Jul 21 '21 at 18:59

John Gordon

29,573
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score 0 · Answer 4 · answered Jul 21 '21 at 19:03

You can use isinstance() to check whether it's a FunctionType or not:

from types import FunctionType

def mainfunction():
    d = {
        'x': secondfunc,
        'y': 'hello world'
    }
    while True:
        inpt = input('@')
        res = d.get(inpt, 'default')
        if isinstance(res, FunctionType):
            res()
        else:
            print(res)

def secondfunc():
    print('hi world')

mainfunction()

How do I store and then call strings and functions from the same dictionary?

First example

Second example

Last example

4 Answers4