Multiple Assignment in Python

In Python, the = operator is used to assign values to variables.

a = 100
b = 200

print(a)
# 100

print(b)
# 200

You can assign values to multiple variables in one line.

Assign multiple values to multiple variables

You can assign multiple values to multiple variables by separating them with commas ,.

a, b = 100, 200

print(a)
# 100

print(b)
# 200

You can assign values to more than three variables, and it is also possible to assign values of different data types to those variables.

a, b, c = 0.1, 100, 'string'

print(a)
# 0.1

print(b)
# 100

print(c)
# string

When only one variable is on the left side, values on the right side are assigned as a tuple to that variable.

a = 100, 200

print(a)
print(type(a))
# (100, 200)
# <class 'tuple'>

If the number of variables on the left does not match the number of values on the right, a ValueError occurs. You can assign the remaining values as a list by prefixing the variable name with *.

# a, b = 100, 200, 300
# ValueError: too many values to unpack (expected 2)

# a, b, c = 100, 200
# ValueError: not enough values to unpack (expected 3, got 2)

a, *b = 100, 200, 300

print(a)
print(type(a))
# 100
# <class 'int'>

print(b)
print(type(b))
# [200, 300]
# <class 'list'>

*a, b = 100, 200, 300

print(a)
print(type(a))
# [100, 200]
# <class 'list'>

print(b)
print(type(b))
# 300
# <class 'int'>

For more information on using * and assigning elements of a tuple and list to multiple variables, see the following article.

• Unpack a tuple and list in Python

You can also swap the values of multiple variables in the same way. See the following article for details:

• Swap values ​​in a list or values of variables in Python

Assign the same value to multiple variables

You can assign the same value to multiple variables by using = consecutively.

For example, this is useful when initializing multiple variables with the same value.

a = b = 100

print(a)
# 100

print(b)
# 100

After assigning the same value, you can assign a different value to one of these variables. As described later, be cautious when assigning mutable objects such as list and dict.

a = 200

print(a)
# 200

print(b)
# 100

You can apply the same method when assigning the same value to three or more variables.

a = b = c = 'string'

print(a)
# string

print(b)
# string

print(c)
# string

Be careful when assigning mutable objects such as list and dict.

If you use = consecutively, the same object is assigned to all variables. Therefore, if you change the value of an element or add a new element in one variable, the changes will be reflected in the others as well.

a = b = [0, 1, 2]

print(a is b)
# True

a[0] = 100
print(a)
# [100, 1, 2]

print(b)
# [100, 1, 2]

b = [0, 1, 2]
a = b

print(a is b)
# True

a[0] = 100
print(a)
# [100, 1, 2]

print(b)
# [100, 1, 2]

If you want to handle mutable objects separately, you need to assign them individually.

after c = []; d = [], c and d are guaranteed to refer to two different, unique, newly created empty lists. (Note that c = d = [] assigns the same object to both c and d.) 3. Data model — Python 3.11.3 documentation

a = [0, 1, 2]
b = [0, 1, 2]

print(a is b)
# False

a[0] = 100
print(a)
# [100, 1, 2]

print(b)
# [0, 1, 2]

You can also use copy() or deepcopy() from the copy module to make shallow and deep copies. See the following article.

• Shallow and deep copy in Python: copy(), deepcopy()