10.22. Functions that Produce ListsΒΆ
The pure version of doubleStuff
above made use of an
important pattern for your toolbox. Whenever you need to
write a function that creates and returns a list, the pattern is
usually:
initialize a result variable to be an empty list
loop
create a new element
append it to result
return the result
Let us show another use of this pattern. Assume you already have a function
is_prime(x)
that can test if x is prime. Now, write a function
to return a list of all prime numbers less than n:
def primes_upto(n):
""" Return a list of all prime numbers less than n. """
result = []
for i in range(2, n):
if is_prime(i):
result.append(i)
return result
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