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pythonif-statementfor-loopsumlist-comprehension
im7
im7

Reputation: 673

Summing the odd numbers in a list using list comprehension, for and if in one line

I am learning Python and I am trying out some exercises. I am trying to sum all the odd numbers from 0 to 9 using list comprehension, for and if in one line.

I tried the following code:

for idx in range(10): s = 0 if idx == 0 else s = [(i % 2) for i in range(10)][idx] * range(10)[idx] + s

but I get the following error:

SyntaxError: can't assign to conditional expression

I don't quite understand it.

Your advice will be appreciated.

Upvotes: 2

Views: 8482

Answers (6)

bindhu
bindhu

Reputation: 1

numbers = range(0, 10)

def addOddNumbers(numbers):
    for num in numbers:
        if num % 2 == 1:
            return sum
        print sum(numbers)

if __name__ == '__main__':
    addOddNumbers(numbers)

Upvotes: 0

Sarath Sadasivan Pillai
Sarath Sadasivan Pillai

Reputation: 7091

This is how you may do it

sum([x for x in range(1,10,2)])

Explaining why your code failed

Here is your code as given in the question

for idx in range(10):
    s = 0 if idx == 0 else ([(i % 2) for i in range(10)][idx] * range(10)[idx] + s)

in the else part you may give the value to be assigned to s ie, s= is not required.You may re-write it as

for idx in range(10):
    s = 0 if idx == 0 else ([(i % 2) for i in range(10)][idx] * range(10)[idx] + s)

The expression syntax for ternary operator in python is as follows

condition_is_true if condition else condition_is_false

Eg usage

value1 = 10
value2 = 20
a = 3
b = 4
value = value1 if a > b else value2
print value
#20

Upvotes: 3

Jean-François Fabre
Jean-François Fabre

Reputation: 140168

very short oneliner:

sum(range(1,10,2))

but the real formula is for any n:

((n+1)//2)**2

With that one, you're able compute the sum for a very big n very quickly.

Back to the point, you cannot accumulate using a list comprehension, or it's very difficult/hacky to do, so sum is required here. So the most logical if requirements are "use a comprehension notation and an if" is:

sum(x for x in range(1,10) if x % 2)

Note that there's no need to put an extra [] in that case. It's a generator comprehension (avoids generating an extra list, sum doesn't need to have all the info at once.

Upvotes: 7

bobtt
bobtt

Reputation: 73

you can one line it this reduce 

reduce(lambda x,y: x+y if y%2 != 0 else x ,range(10))

output

25

Upvotes: 1

Shivkumar kondi
Shivkumar kondi

Reputation: 6762

you can do this ..

a = range(0,10)
b = sum([x for x in a if x%2 != 0])
print b

output :

25

Upvotes: 0

José Sánchez
José Sánchez

Reputation: 1146

You can try this:

sum([x for x in range(10) if x % 2 != 0])

First you create a list of number from 0 to 9 with range, then you create the list (list comprehension) of the odd numbers (using if x % 2). Finally, you sum the contents of the array using sum.

Upvotes: 2

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