CODEWITHSUNDEEP
pythonclassmethods
sebach1
sebach1

Reputation: 117

Pass method as a parameter on python

Can I pass a method as a parameter on python? I want to do things like, for example, if anything is an instance of an object w/has foo method:

def access_to(class=anything, method="foo"): return class.method

(Note is obvious that Anything instance doesn't have the attribute 'method', and Ill get an AttributeError).

Upvotes: 0

Views: 139

Answers (2)

tdurnford
tdurnford

Reputation: 3712

You certainly can pass a method as a parameter to a function in Python. In my example below, I created a class (MyClass) which has two methods: isOdd and filterArray. I also created an isEven function outside of MyClass. The filterArray takes two parameters - an array and a function that returns True or False - and uses the method passed as a parameter to filter the array.

Additionally, you can pass lambda functions as parameter, which is like creating a function on the fly without having to write a function declaration. 

def isEven(num):
    return num % 2 == 0

class MyClass:

    def isOdd(self, num):
        return not isEven(num)

    def filterArray(self, arr, method):
        return [item for item in arr if method(item)]

myArr = list(range(10))  # [0, 1, 2, ... 9]

myClass = MyClass()

print(myClass.filterArray(myArr, isEven))
print(myClass.filterArray(myArr, myClass.isOdd))
print(myClass.filterArray(myArr, lambda x: x % 3 == 0))

Output:

[0, 2, 4, 6, 8]
[1, 3, 5, 7, 9]
[0, 3, 6, 9]

Upvotes: 0

Corentin Limier
Corentin Limier

Reputation: 5016

Uses getattr if you want to get the method from a string parameter.

class A:
    def foo(self):
        print("foo")

def access_to(c, method="foo"):
     return getattr(c, method)

a = A()
b = 5
access_to(a)()
access_to(b)()

It prints foo for a, then it raises error for b

I have to say that I recommend not to abuse this type of functions unless you have to for some specific reasons.

Upvotes: 4

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