Cannot convert string into float in a for loop

Question

I'm trying to convert a string (such as 10.99) into a float in a for loop, and I can't figure out a way to do it with the data I've scraped from a website. I need to divide the output by another float (also in the for loop). The below is an example of what I'm trying to do

import re

test_data = ['\n\t\t\t\t£10.00 per 100ML', '\xa0', '\n\t\t\t\t£0.40 per EACH', '\xa0', '\xa0', '\xa0', '\xa0', '\n\t\t\t\t£0.54 per EACH', '\n\t\t\t\t£1.33 per EACH']
price_data = [100, 10.99, 20.99, 25.25, 30, 35, 40, 54, 3]

for items in zip(test_data, price_data):
    characters = re.sub("\[p].*$|[^\d\.]", "", items[0])
    price_per_unit = characters[0:5]

    price = items[1]

    number_of_units = price / float(price_per_unit)

I then get the error:

    number_of_units = price / float(price_per_unit)
ValueError: could not convert string to float:

What's the best way to turn price_per_unit into a float, and calculate number_of_units??

Thanks for your help :)

EDIT: Working solution below for anyone else who's interested

import re

test_data = ['\n\t\t\t\t£10.00 per 100ML', '\xa0', '\n\t\t\t\t£0.40 per EACH', '\xa0', '\xa0', '\xa0', '\xa0', '\n\t\t\t\t£0.54 per EACH', '\n\t\t\t\t£1.33 per EACH']
price_data = [100, 10.99, 20.99, 25.25, 30, 35, 40, 54, 3]

for items in zip(test_data, price_data):
    price = items[1]

    characters = re.sub("\[p].*$|[^\d\.]", "", items[0])
    price_per_unit = characters[0:5]
    if price_per_unit.replace('.', '', 1).isdigit():
        price_per_unit_formatted = float(price_per_unit)
        number_of_units = price / price_per_unit_formatted
    else:
        price_per_unit = None
        number_of_units = None

You need to cast both operands into floats to be compatible. — Maximilian Burszley
– Maximilian Burszley, Commented Dec 4, 2019 at 16:34
Your re.sub() part is not working good, It doesn't return any data. I don't get what were you trying to achieve. — furkanayd
– furkanayd, Commented Dec 4, 2019 at 16:49

Bill Chen · Accepted Answer · 2019-12-04 16:43:48Z

3

Your problem is not from the float() function. When the code parses the test_data, the '\xa0' will return an empty string '', this empty string cannot be converted to float point value.

Hope this helps.

answered Dec 4, 2019 at 16:43

Bill Chen

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David · Accepted Answer · 2019-12-04 16:47:44Z

1

As Bill said, your problem is due to the fact that some of price_per_unit are ''. a simple wrap around this issue is making sure that the price_per_unit is indeed a number for instance in the following way:

if price_per_unit.replace('.','',1).isdigit():
      number_of_units = price / float(price_per_unit)

This will ignore those '' and still maintain its functionality

answered Dec 4, 2019 at 16:47

David

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1 Comment

siblackburn Over a year ago

Super helpful thank you @David S! I've taken your suggestion and added it to my code, working perfectly:

bcosta12 · Accepted Answer · 2019-12-04 16:50:07Z

1

the \xa0 is becoming a empty string, you should handle it

import re

test_data = ['\n\t\t\t\t£10.00 per 100ML', '\xa0', '\n\t\t\t\t£0.40 per EACH', '\xa0', '\xa0', '\xa0', '\xa0', '\n\t\t\t\t£0.54 per EACH', '\n\t\t\t\t£1.33 per EACH']
price_data = [100, 10.99, 20.99, 25.25, 30, 35, 40, 54, 3]

for items in zip(test_data, price_data):

    characters = re.sub("\[p].*$|[^\d\.]", "", items[0])

    price_per_unit = characters[:5]
    if price_per_unit == '':
      print('empty')
      break
    price = items[1]

    number_of_units = price/ float(price_per_unit)
    print(number_of_units)

answered Dec 4, 2019 at 16:50

bcosta12

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Comments

Enrico Belvisi · Accepted Answer · 2019-12-04 16:56:18Z

1

if I understand what you're asking for:

number_of_units=[]
for items in zip(test_data, price_data):
  if (items[0]!='\xa0'):
    characters = re.sub("\[p].*$|[^\d\.]", "", items[0])
    price_per_unit = characters[0:5]

    price = items[1]

    number_of_units.append(price / float(price_per_unit))
  else:
    number_of_units.append(1)

number_of_units #[10.0, 1, 52.474999999999994, 1, 1, 1, 1, 100.0, 2.255639097744361]

considered '\xa0' elements as 1 indivisible unit.

Using a list to store all the values generated in the loop, with your code you would store only the last.

edited Dec 4, 2019 at 16:56

answered Dec 4, 2019 at 16:47

Enrico Belvisi

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Comments

NiTiN · Accepted Answer · 2019-12-05 04:13:15Z

When you are doing SUBSTR of Test_Data where string like '\xa0' exists then it's giving an empty string in your price_per_unit variable. To avoid this you can replace it with '1' as replacing with '0' would give an error of division by zero.

    import re

test_data = ['\n\t\t\t\t£10.00 per 100ML', '\xa0', '\n\t\t\t\t£0.40 per EACH', '\xa0', '\xa0', '\xa0', '\xa0', '\n\t\t\t\t£0.54 per EACH', '\n\t\t\t\t£1.33 per EACH']
price_data = [100, 10.99, 20.99, 25.25, 30, 35, 40, 54, 3]

for items in zip(test_data, price_data):
    characters = re.sub("\[p].*$|[^\d\.]", "", items[0])
    price_per_unit = characters[0:5]


    price = items[1]

    if price_per_unit == '':
      price_per_unit = '1'
    else:
      price_per_unit

    print('---------')
    number_of_units = price / float(price_per_unit)
    print(number_of_units)

For better understanding of errors it's better to print the variable when you get an error. That's how I came to know why this issue was occurring.

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