CS115 – Hw 1
Writing your own factorial function
def mult(x, y):
"""Returns the product of x and y"""
return x * y
Nothing too surprising here. Now, take a look at this:
>>> reduce(mult, [2, 3])
6
>>> reduce(mult, [2, 3, 4])
24
>>> reduce(mult, [1, 2, 3, 4])
24
Notice that reduce takes two inputs: A function and a list and it applies that function to "compress"
the list into a single value. In this case, it multiplied all of the values together.
Now, write a function factorial(n) that takes a positive integer n and returns n!.
This is "mean"...
Finally, write a function called mean(L) that takes a list as input and returns the mean (average)
value in that list. Using reduce will be handy here. You may also want to define an add function that
As shown above, we can use the factorial function from the math module. Here, you'll write your
own factorial function. First, we start with a simple function that returns the product of its two inputs:
>>> factorial(5)
>>> 120
>>> f r o m m a t h i m p o r t factorial
CS115 – Hw 1
returns the sum of two numbers. You'll need to know the number of elements in the list. This can be
found using the built-in function len. For example:
>>> len([1, 3, 5])
3
>>> len(range(1,10))
9
Here is the mean function in action:
>>> mean([1, 2, 3])
2
>>> mean([1, 1, 1])
1
CS115 – Hw 1
