In the previous exercise you calculated the mean weight of the Cambridge crew and then the mean weight of the Oxford crew. You surely noticed that writing the code to calculate Oxford's mean was pretty easy since it used the same procedure as the code to calculate Cambridge's mean.
The process for calculating the mean is:
When working with code, it's common to find yourself repeating a calculation many times. Computer programmers don't like to repeat themselves, so, to save yourself time, you can put the calculation into a function. When you define a function, it's like a recipe for serving ice cream:
Before you can use your own function, you must define the function. Defining a function is similar to how dictionaries define words.
You will now define one function, calling it mean(), and the use mean() to calculate stuff. Type this code:
# create the mean() function def mean(myData): return sum(myData) / len(myData) # Test the function print "I know the average of 2.0, 2.0, and 5.0 to be 3.0." print "My function says the average is:" print mean( [2.0, 2.0, 5.0] ) print # Calculate the rowing teams' means cambridgeWeights = [188.5, 183, 194.5, 185, 214, 203.5, 186, 178.5, 109] oxfordWeights = [186, 184.5, 204, 184.5, 195.5, 202.5, 174, 183, 109.5] print "The average weight for Cambridge is:" print mean(cambridgeWeights), "pounds" print "and the average weight for Oxford is:" print mean(oxfordWeights), "pounds" print print "This is a difference of:" print mean(cambridgeWeights) - mean(oxfordWeights), "pounds "
Save the program as my-mean-function.py.
After clicking Run, you should get:
I know the average of 2.0, 2.0, and 5.0 to be 3.0. My function says the average is: 3.0 The average weight for Cambridge is: 182.444444444 pounds and the average weight for Oxford is: 180.388888889 pounds This is a difference of: 2.05555555556 pounds
By making your own function, you just saved yourself a lot of work, since you didn't have to calculate by hand the averages.
Programmers are lazy, so they make the computer do as much work as possible. This means there is more time to get ice cream. Hooray for functions.