Functions
Functions allow us to reuse and organize code. For example, say we have some code that calculates the area of a circle:
radius = 5
area = 3.14 * radius * radius
That works! The problem is when we want to calculate the area of other circles, each with its own radius. We could just copy the code and change the variable names like this:
radius = 5
area1 = 3.14 * radius * radius
radius2 = 7
area2 = 3.14 * radius2 * radius2
But we want to reuse our code! Why would we want to redo our work? What if we wanted to calculate the area of thousands of circles??? That's where functions help.
Instead, we can define a new function called area_of_circle using the def keyword.
def area_of_circle(r):
pi = 3.14
result = pi * r * r
return result
Let's break this area_of_circle function down:
- It takes one input (aka "parameter" or "argument") called
r - The body of the function is indented - this is the code that will run each time we use (aka "call") the function
- It
returns a single value (the output of the function). In this case, it's the value stored in theresultvariable
To "call" this function (fancy programmer speak for "use this function") we can pass in any number as the argument (in this case, 5) for the parameter r, and capture the output into a new variable:
area = area_of_circle(5)
print(area)
# 78.5
5goes in as the inputr- The body of the function runs, which stores
78.5in theresultvariable - The function returns the value
78.5, which means thearea_of_circle(5)expression evaluates to78.5 78.5is stored in theareavariable and then printed
Because we've already defined the function, now we can use it as many times as we want with different inputs!
area = area_of_circle(6)
print(area)
# 113.04
area = area_of_circle(7)
print(area)
# 153.86
Assignment
We need to calculate the size of a weapon's "attack area". With a 1.0 meter sword, for example, a player can attack in an area of 3.14 square meters around them. You can use the area_of_circle function to do that calculation.
Fix the bug on line 13 by calling the area_of_circle function with the spear_length as input and store the result in the spear_area variable.