CODEWITHSUNDEEP
python
Mohamad Zein
Mohamad Zein

Reputation: 777

How to call a function inside a dictionary in python

I am creating a python shell script that will allow the user to enter commands that output a string. But also some commands will call a function, like help, or exit I know python does not have a switch case so I am using a dictionary instead, as I do not want to use if and else statements

The problem:

The problem is I cannot use a function call inside the dictionary with the way I have it implemented as it expects to output a string, so when I enter help I get an error

    #!/usr/bin/python

    x = 0
    while x == 0:



        def helpCommand():
            print "this will help you"

        switcher = {
           "url": " the url is: ... ",
           "email": " my email is: ...",
           "help": helpCommand,
           "exit": exit,
        }

        choice = raw_input("enter your command choice: ")

        def outputChoice(choice)
            return switcher.get(choice)

        print outputChoice(choice)

I tried to solve this problem by using function call instead, but now I get an error when trying to call a string

 def outputChoice(choice)
                    return switcher[choice]()

TypeError: 'str' object is not callable

How to fix this problem ?

Upvotes: 1

Views: 7120

Answers (2)

hecke
hecke

Reputation: 236

You can try to call the function, and if it fails, print the string. iirc this is the pythonic way - it is easier to ask for forgiveness then for permission (or in this case, the callable attribute).

def bar():
    print 'foo'

gru = { 'dead': 'beef',
        'foo' : bar}

for what in [ 'dead', 'foo']:
    try:
        gru[what]()
    except TypeError:
        print gru[what]

Upvotes: 1

PM 2Ring
PM 2Ring

Reputation: 55469

Djizeus's suggestion of callable() makes this simple.

Your code organization is a bit odd. You shouldn't normally put function definitions inside a loop, since that causes the function to be redefined on every loop, which is pointless and inefficient.

Here's a modified version of your code, using Djizeus's suggestion.

#!/usr/bin/python

def helpCommand():
    print "this will help you"

switcher = {
    "url": " the url is: ... ",
    "email": " my email is: ...",
    "help": helpCommand,
    "exit": exit,
}

def process_choice(choice):
    item = switcher[choice]
    if callable(item):
        item()
    else:
        print item

x = 0
while not x:
    choice = raw_input("Enter your command choice: ")
    process_choice(choice)
    #other stuff that modifies `x`

If nothing in the loop actually modifies x, you can just get rid of that and make the loop into:

while True:
    choice = raw_input("Enter your command choice: ")
    process_choice(choice)

Upvotes: 3

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