CODEWITHSUNDEEP
pythonmathlambda
Tetramputechture
Tetramputechture

Reputation: 2921

Python: Getting the Sum of a Lambda Function

I'm trying to get the sum of all the prime numbers below 2,000,000 in Python, using a lambda function. (I've bruteforced it, but that takes much too long, and I want a better solution.) Here is what I have so far:

def isPrime(n):
    for x in range(2, int(n**0.5)+1):
        if n%x==0: return False
    return True


print reduce(lambda x: isPrime(x), [range(200)])

Now, this just prints numbers incrementing from 1 to 200, so I don't think reduce is working =\

Anyone have any tips?

Upvotes: 1

Views: 2573

Answers (2)

Steve
Steve

Reputation: 1243

There are lots of things wrong here. The first is that you can replace lambda x: isPrime(x) with simply isPrime. Functions are first class in Python, which means you can just pass them around in the same way as integers or strings. The second is that you are passing a list of lists; [range(200)] is a list containing the return value of range(200) range returns a list so you are only reducing a single value. This gets around the third problem, which is that your reduce function should accept 2 arguments, as reduce calls the function passed on pairs of items as a time. As it is, there is only one item so the function is called 0 times and the first item on list is returned.

What I suspect you want to do is to filter the list, you can use the filter function to do this or you can use a list comprehension which would look like this:

[x for x in range(200) if isPrime(x)]

Upvotes: 2

Andrew Clark
Andrew Clark

Reputation: 208485

There are a few odd things going on with your code.

  • I think you actually want to be using filter(), not reduce().
  • lambda x: isPrime(x) is equivalent to isPrime (after all, isPrime is already a function that returns the result of isPrime).
  • [range(200)] creates a nested list. The only element in the outer list is a list with the numbers from 0 to 200. I think you just want the single list.

So, try the following:

print filter(isPrime, range(200))

Upvotes: 2

Related Questions