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](https://stackoverflow.com/help/mcve). — Alex, Aug 08 '18 at 17:14
Possible duplicate of [How do I parse a string to a float or int in Python?](https://stackoverflow.com/questions/379906/how-do-i-parse-a-string-to-a-float-or-int-in-python) — Evan Edwards, Aug 08 '18 at 17:15
@EvanEdwards May not be the duplicate as OP knows how to parse — mad_, Aug 08 '18 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, Aug 08 '18 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, Aug 08 '18 at 17:21

score 1 · Accepted Answer · answered Aug 08 '18 at 17:26

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.

score 0 · Answer 2 · answered Aug 08 '18 at 17:26

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.

how to convert from string to float in python?

2 Answers2