Trying to use reduce () and lambda with a list containing strings

Question

I am trying to use the pythons abbreviation function in a list containing strings of integers.

print int("4") \\Gives me 4 Good print reduce(lambda x, y: x*y, [2, 3, 4]) \\Gives me 24 Good print reduce(lambda x, y: x*int(y), ['2', '3', '4']) \\Gives me 222222222222 What?? 

I assume the abbreviation gives lambda functions something that is not the actual line in the list? I have no idea why I am getting 222222222222 at least will there be an easy way to make an int list? I think I could just create another loop, but I still would like to know what happened with the line feed.

Answer 1

 >>> reduce(lambda x, y: x*int(y), ['2', '3', '4']) '222222222222' 

Ok, here's what happens:

At the first reduction stage, the following calculation is performed: '2' * 3 . Since the first operand is a string, it just repeats 3 times. That way you get '222' .

In the second reduction step, this value is multiplied by 4: '222' * 4 . Again, the line is repeated four times, resulting in '222222222222' , which is exactly the result you got.

You could avoid this by converting x to int also (calling int(x) ) or by matching list items using integer conversion in the first place (I actually think this is more elegant):

 >>> reduce(lambda x, y: x * y, map(int, ['2', '3', '4'])) 24 

Answer 2

You can try the following:

 reduce(lambda x, y: x*int(y), ['2', '3', '4'], 1) 

Notice that I pass the third parameter to reduce , indicating that the operation should be initialized to 1 , a multiplicative identity. Thus, you only need to convert y , the current value to int , and not x , the accumulated value.

Answer 3

You multiply the string '2' by int 3, which gives the string '222' ... then the string '222' by int 4, which gives the string '222222222222'.

You need to convert x to an integer:

 print reduce(lambda x, y: int(x)*int(y), ['2', '3', '4']) 

Answer 4

 multiply = lambda a,b: a*b listOfInts = map(int, ['2','3','4']) reduce(multiply, listOfInts) #output: 24