CODEWITHSUNDEEP
python
Randomblue
Randomblue

Reputation: 116293

Force default reevaluation on function call

AFAIK, Python evaluates the defaults of a function only once, at declaration time. So calling the following function printRandom

import random
def printRandom(randomNumber = random.randint(0, 10)):
    print randomNumber

will print the same number each time called without arguments. Is there a way to force reevaluation of the default randomNumber at each function call without doing it manually? Below is what I mean by "manually":

import random
def printRandom(randomNumber):
    if not randomNumber:
         randomNumber = random.randint(0, 10)
    print randomNumber

Upvotes: 1

Views: 327

Answers (3)

Gandaro
Gandaro

Reputation: 3443

I think the best bet would be to define None as default value for randomNumber.

def printRandom(randomNumber=None):
    if randomNumber is None:
        print random.randint(0, 10)
    else:
        print randomNumber

Upvotes: 2

detly
detly

Reputation: 30342

Use None:

def printRandom(randomNumber=None):
    if randomNumber is None:
        randomNumber = random.randint(0, 10)
    print randomNumber

Upvotes: 3

Katriel
Katriel

Reputation: 123662

No. The default arguments are set when they are executed, which is when the function is defined. If you wanted them to be re-executed, you would need to re-define the function.

The standard idiom, and the one you should use, is

import random
def print_random(random_number=None):
    if random_number is None:
        random_number = 4 # chosen by fair dice roll.
                          # guaranteed to be random.
    print random_number

Note the use of None (a singleton) and the is test for object identity. You shouldn't use if not random_number since there are many values which evaluate to boolean false -- in particular, 0.

There are plenty of other ways you could do this, but there's no reason not to follow the convention.

Upvotes: 6

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