could not convert string to float (python)

Question

I am trying to find the sum of all numbers in a list but every time I try I get an error that it cannot convert the string to float. Here is what I have so far.

Answer 1

'elec_used' is of type string of characters. You can not convert characters to the float. I am not sure why you thought you could do it. However you can convert the numeric string to float by typecasting it. For example:

>>> number_string = '123.5'
>>> float(number_string)
123.5

Now coming to your second part, for calculating the sum of number. Let say your are having the string of multiple numbers. Firstly .split() the list, type-cast each item to float and then calculate the sum(). For example:

>>> number_string = '123.5 345.7 789.4'
>>> splitted_num_string = number_string.split()
>>> number_list = [float(num) for num in splitted_num_string]
>>> sum(number_list)
1258.6

Which could be written in one line using list comprehension as:

>>> sum(float(item) for item in number_string.split())
1258.6

OR, using map() as:

>>> sum(map(float, number_string.split()))
1258.6