how to convert from string to float in python?

Question

I am trying to convert text from a csv file to a floating point number. But i keep getting the error: ValueError: could not convert string to float: year. I am getting the same error when trying to convert to int. The number that is imported is 2018.0

 import csv
 with open('test_csv.csv', 'rb') as data_file:
      data = csv.reader(data_file, delimiter=',')
      for i in data:
         year  = float(i[0])

Can you share the first few lines of the CSV? So that this is a Minimal, Complete, and Verifiable example. — Alex
– Alex, Commented Aug 8, 2018 at 17:14
Possible duplicate of How do I parse a string to a float or int in Python? — Evan Edwards
– Evan Edwards, Commented Aug 8, 2018 at 17:15
@EvanEdwards May not be the duplicate as OP knows how to parse — mad_
– mad_, Commented Aug 8, 2018 at 17:16
There is likely some hidden character or something, can you print repr(i) and make sure it is just 2018.0 — bison
– bison, Commented Aug 8, 2018 at 17:17
Are you sure that the index you point to is ALWAYS in the format you expect it to be? Please provide the format of the CSV file — Riley Hughes
– Riley Hughes, Commented Aug 8, 2018 at 17:21

Green Cloak Guy · Accepted Answer · 2018-08-08 17:26:26Z

1

Based on the error message you're getting, your issue is probably with the first line of your CSV. You haven't actually shared the contents of the file, but if I had to guess, it looks like this:

year,  some_value,    some_value,    ...
2018,  ...       ,    ...       ,    ...
2017,  ...       ,    ...       ,    ...

Your code is getting tripped up with the year that's on the first line of your CSV. The solution, then, is probably to skip that first line, or use a DictReader instead of a reader.

answered Aug 8, 2018 at 17:26

Green Cloak Guy

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OMY · Accepted Answer · 2018-08-08 17:26:53Z

0

Try this:

 import csv
 with open('test_csv.csv', 'rb') as data_file:
      data = csv.reader(data_file, delimiter=',')
      for i in data:
         try:
             year  = float(i[0])
         except ValueError as e:
             print("Couldn't convert the following line {0}".format(i))

You probably have either a last empty line, (which creates a one empty cell array and cannot be converted) or a wrong row in your file.

answered Aug 8, 2018 at 17:26

OMY

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