# How does Python reassign a variable's value?

### Question

If a variable already has a value, how do we change that value later by reassigning a new value?

We can think of variables as being little boxes that are able to store values. In this exercise, we’ve labeled our box `annual_rainfall` and put the value of `january_to_june_rainfall` in it at first. When we assign a new value in that same variable, the number in our box is replaced by the values for the months from September through December.

### In-depth Look at the Exercise

``````january_to_june_rainfall = 1.93 + 0.71 + 3.53 + 3.41 + 3.69 + 4.50
annual_rainfall = january_to_june_rainfall

july_rainfall = 1.05
annual_rainfall += july_rainfall

august_rainfall = 4.91
annual_rainfall += august_rainfall

september_rainfall = 5.16
october_rainfall = 7.20
november_rainfall = 5.06
december_rainfall = 4.06
``````

The very first line of code, `january_to_june_rainfall = 1.93 + 0.71 + 3.53 + 3.41 + 3.69 + 4.50`, assigns the result of that addition to the variable named `january_to_june_rainfall`.
After that, three examples of using the `+=` operator are given to give you an idea of how to update an existing variable’s value, `annual_rainfall`.
September through December, then, are the months we haven’t added to the existing variable’s value, which is the goal of the exercise.

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