Python Function and Scope - The function can update outer list, set, dictionary but can't change integer, float, string

Can Python function access or update outer variables? It depends on the type as follows.

a = ''
b = []


def f():
    a = 'Apple'
    b.append('x')


f()
print(a)
print(b)

a is string and not hasn't updated by f. But f has appended to list b. So Python function...

• can update the outer list
• can NOT update the outer string

Python function can't update the outer integer, float, string

a = 2
b = 3.14
c = 'JavaScript'


def f():
    a = 3
    b = 4.5
    c = 'PHP'


f()

print(a)  # 2
print(b)  # 3.14
print(c)  # JavaScript

Python function can add the outer list, set, dictionary

a = [5, 9]
b = {'PHP', 'HTML'}
c = {'x': 1, 'y': 2}


def f():
    a.append(100)
    b.add('CSS')
    c['z'] = 3


f()

print(a)  # [5, 9, 100]
print(b)  # {'CSS', 'HTML', 'PHP'}
print(c)  # {'x': 1, 'y': 2, 'z': 3}

You may think the function can only add and can't replace the value. But it can actually update list as follows.

a = [5, 9]


def f():
    a[0] = 7


f()

print(a)  # [7, 9]

Id and scope

a = [5, 9]

print(id(a))  # 4535348096


def f():
    print(id(a))  # 4535348096
    a[0] = 7


f()

print(id(a))  # 4535348096

As you see, id of a is the same in outer or inner scope.

Python function can't update a string but access

a = 'Apple'


def f():
    print(a)


f()

# Apple