How do chained assignments work in Python, and what are the potential pitfalls when dealing with mutable objects?

How do chained assignments work?

A chained assignment in Python, such as:

x = y = somefunction()

is equivalent to the following two statements executed sequentially:

temp = somefunction()
x = temp
y = temp

This means that the expression on the right-hand side of the assignment operator is evaluated first, and the resulting value is then assigned to all of the variables on the left-hand side, from left to right.

For example, the following code will print the number 10 twice:

def somefunction():
    return 10

x = y = somefunction()
print(x)
print(y)

It's important to note that chained assignments can be problematic when dealing with mutable objects, such as lists. For example, the following code assigns the same empty list to both x and y:

x = y = []

x.append(1)

print(x)
print(y)

This will print [1, 1] because both x and y refer to the same list. If you intended to create two separate lists, you should instead write:

x = []
y = []

x.append(1)

print(x)
print(y)

This will print [1] and [] because x and y refer to different lists.

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