Pass by value and Pass by reference in python

Pass by value (call by value) and Pass by reference (call by reference) :

Pass by value (call by value):

•  Original value is not modified in call by value.

•  In call by value, value being passed to the function is locally stored by the function parameter in stack memory location. 

•  If you change the value of function parameter, it is changed for the current function only.

Example:

a=10

def f1(x):

    print(x)

    x=20

    print(x)

f1(a)

print(a)

Output:

10

20

10

pass by reference (call by reference):

• In call by reference, original value is modified because we pass reference (address).

• Here, address of the value is passed in the function, so actual and formal arguments shares the same address space. 

• value changed inside the function, is reflected inside as well as outside the function.

Example:

b=[1,2,3]

def f2(y):

    print(y)

    y[0]=10

    y[1]=20

    print(y)

f2(b)

print(b)

Output:

[1, 2, 3]

[10, 20, 3]

[10, 20, 3]