Python Tutorial: Pass by assignment

Want to learn more? Take the full course at https://learn.datacamp.com/courses/writing-functions-in-python at your own pace. More than a video, you'll learn hands-on coding & quickly apply skills to your daily work. --- The way that Python passes information to functions is different from many other languages. It is referred to as "pass by assignment", which I will explain in this lesson. Let's say we have a function foo() that takes a list and sets the first value of the list to 99. Then we set "my_list" to the value [1, 2, 3] and pass it to foo(). What do you expect the value of "my_list" to be after calling foo()? If you said "[99, 2, 3]", then you are right. Lists in Python are mutable objects, meaning that they can be changed. Now let's say we have another function bar() that takes an argument and adds ninety to it. Then we assign the value 3 to the variable "my_var" and call bar() with "my_var" as the argument. What do you expect the value of "my_var" to be after we've called bar()? If you said "3", you're right. In Python, integers are immutable, meaning they can't be changed. Let's look at another example to understand what's going on. Imagine that this gray bar is your computer's memory. When we set the variable "a" equal to the list [1, 2, 3], the Python interpreter says, "Okay, now 'a' points to this location in memory." Then if we type "b = a", the interpreter says, "Okay, now 'b' points to whatever 'a' is pointing to." So if we were to append 4 to the end of "a", both variables get it because there is only one list. Likewise, if we append 5 to "b", both variables get it. However, if we assign "a" to a different object in memory, that does not change where "b" is pointing. Now, things that happen to "a" are no longer happening to "b", and vice versa. How does this relate to the example functions we saw earlier? When we assign a list to the variable "my_list", it sets up a location in memory for it. Then, when we pass "my_list" to the functio