How do you sum only positive numbers in a list python?

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Given a list. The task is to find the sum of Negative, Positive Even, and Positive Odd numbers present in the List.

Examples:

Negative numbers are the numbers less than 0 while positive even numbers are numbers greater than 0 and also divisible by 2. 0 is assumed to be a positive even number, in this case. 

Approach:

• The first approach input a list of numbers from the user.
• Two loops are run, one for the positive numbers and the other for the negative numbers, computing the numbers’ summation.
• If n is the size of the list of numbers,
• it takes O(2n) time complexity, for iterating over the list of numbers twice.

Python3

class Sumofnumbers:

    def negSum(self, list):

        neg_sum = 0

        for num in list:

            num = int(num)

            if(num < 0):

                neg_sum + = num

        print("Sum of negative numbers is ", neg_sum)

    def posSum(self, list):

        pos_even_sum = 0

        pos_odd_sum = 0

        for num in list:

            num = int(num)

            if(num >= 0):

                if(num % 2 == 0):

                    pos_even_sum + = num

                else:

                    pos_odd_sum + = num

        print("Sum of even positive numbers is ",

              pos_even_sum)

        print("Sum of odd positive numbers is ",

              pos_odd_sum)

list_num = [-7, 5, 60, -34, 1]

obj = Sumofnumbers()

obj.negSum(list_num)

obj.posSum(list_num)

Output:

The second approach computes the sum of respective numbers in a single loop. It maintains three counters for each of the three conditions, checks the condition and accordingly adds the value of the number in the current sum . If n is the size of the list of numbers, it takes O(n) time complexity, for iterating over the list of numbers once. 

Python3

class Sumofnumbers:

    def Sum(self, list):

        neg_sum = 0

        pos_even_sum = 0

        pos_odd_sum = 0

        for num in list:

            num = int(num)

            if(num < 0):

                neg_sum += num

            else:

                if(num % 2 == 0):

                    pos_even_sum + = num

                else:

                    pos_odd_sum + = num

        print("Sum of negative numbers is ",

              neg_sum)

        print("Sum of even positive numbers is ",

              pos_even_sum)

        print("Sum of odd positive numbers is ",

              pos_odd_sum)

list_num = [1, -1, 50, -2, 0, -3]

obj = Sumofnumbers()

obj.Sum(list_num)

Output: 

Method: Using list comprehension 

Python3

lst = [1, -1, 50, -2, 0, -3];i=0

x=[i for i in lst if i>0 and i%2==0]

y=[i for i in lst if i>0 and i%2!=0]

z=[i for i in lst if i<0]

print("even positive numbers sum",sum(x))

print("odd positive numbers sum",sum(y))

print("negative numbers sum",sum(z))

Output

Method: Using the lambda function 

Python3

lst = [1, -1, 50, -2, 0, -3]

x=list(filter(lambda i: (i>0 and i%2==0),lst))

y=list(filter(lambda i: (i>0 and i%2!=0),lst))

z=list(filter(lambda i: (i<0),lst))

print("even positive numbers sum",sum(x))

print("odd positive numbers sum",sum(y))

print("negative numbers sum",sum(z))

Output

Method: Using enumerate function

Python3

lst = ['1', '-1', '50', '-2',' 0', '-3']

x=[int(i) for a,i in enumerate(lst) if int(i)%2==0 and int(i)>0]

y=[int(i) for a,i in enumerate(lst) if int(i)%2!=0 and int(i)>0]

z=[int(i) for a,i in enumerate(lst) if int(i)<0]

print("even positive numbers sum",sum(x))

print("odd positive numbers sum",sum(y))

print("negative numbers sum",sum(z))

Output