How can I modify an integer passed to a function in Python?

Passing an Integer by Reference in Python

In Python, integers are immutable, meaning that once created, their value cannot be changed. This raises the question of how to pass an integer by reference, allowing modifications made within a function to be reflected in the original variable.

Passing a Mutable Container

While it's not possible to pass an integer by reference directly, you can pass it in a mutable container, such as a list:

def change(x):
    x[0] = 3

x = [1]
change(x)
print(x)

Output:

[3]

In this example, we create a list x containing a single element. We then pass x to the change function, which modifies the value at index 0. Since lists are mutable, this change persists even after the function returns.

Returning a New Object

Another option is to return a new object with the modified value from the function:

def multiply_by_2(x):
    return 2 * x

x = 1
x = multiply_by_2(x)

In this case, the multiply_by_2 function returns a new object with the doubled value, which is then assigned to x. The original integer x remains unchanged.

Best Practices

When passing integers to functions, consider the following best practices:

• If you need to modify the value in the original variable, use a mutable container as described above.
• If you only need to use the modified value, return a new object from the function.
• Avoid using global variables, as this can lead to potential conflicts and code readability issues.

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