Lots of substitutions can also happen on one line of code. If there is an assignment, they happen on the right hand side of the =

age = 36
result = add(1, age)
print(result)

When we read this code, it breaks down into steps:

Assign the value of 36 to the variable called age. Move to the next line

On line 2, we need to figure out the value on the right hand side before we can assign it to the variable.

So first, replace the variable age with it’s value at the moment

    result = add( 1, 36 )

Execute the function add to get the result, 37.

Replace the add(1,36) with the result

    result = 37

Then we assign it to the result variable.

Then we move to the next line.

We replace result with it’s value at the moment.

Then we print that value.