CODEWITHSUNDEEP
pythonlist
Sphero
Sphero

Reputation: 333

Can the list method extend be used on a function? (Python 3)

My question is whether a function is can have the list method extend used on it? An example of the function in which I'm trying to understand:

def g(p):
    w = p.pop(1)
    p.extend(w)
    return p
y = ['k', 'l', 'm']
g(y[:]).extend(g(y))

This returns the following value for y:

['k', 'm', 'l']

However I was expecting the following value for y:

['k', 'm', 'l', 'k', 'm', 'l']

Is someone able to explain to me what is happening here? Are functions not allowed to be used as an argument or are they also not allowed to have the list method extend used on them?

Upvotes: 1

Views: 76

Answers (1)

Reblochon Masque
Reblochon Masque

Reputation: 36662

It works as intended:

What is going on, is that:

1- first, y is not mutated, since you are passing a deep copy of it to g. 2- g is mutated when you pass it directly for the second call to g 3- you are not assigning the returned result from g(y)
4- extend returns None

def g(p):
    w = p.pop(1)
    p.extend(w)
    return p
y = ['k', 'l', 'm']

res = g(y[:])      # <- this does not mutate y
res.extend(g(y))   # <- this does mutate y
y, res

output:

                   result from the first call to g
                   |------------|
(['k', 'm', 'l'], ['k', 'm', 'l', 'k', 'm', 'l'])
  |------------|                  |------------|
 y mutated at 2nd call             extended with mutated y from 2nd call

Upvotes: 1

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