Python : ValueError: invalid literal for float()

Question

I'm tring to create a dictionary importing data from an excel file converted in csv and I want to convert the string value of the dictionary into float, but I get in return this error ValueError: invalid literal for float(): 437,33

import csv
from collections import defaultdict

my_dict = {}
my_dict = defaultdict(lambda : 0, my_dict)

with open('excel_csv_file.csv', 'rb') as file_object:
    reader = csv.reader(file_object, delimiter=';')
    for x in reader:
        my_dict[(x[0], x[1])] = x[2]

my_dict = dict((k, float(v)) for k,v in my_dict.iteritems())
print my_dict

This is what my_dict looks like

{('11605', 'TV'): '437,33',
 ('10850', 'SMARTPHONE'): '163,47',
 ('11380', 'TV'): '1911,72',
 ('11177', 'SMARTPHONE'): '255,80',
 ('11237', 'TABLET'): '382,28',
 ('11238', 'TABLET'): '458,01',
 ('11325', 'TABLET'): '309,55',
 ...}

Why am I getting this error?

Also, is there a way to convert the string value inside the tuple key into an int? (for instance ('11605', 'TV') to (11605, 'TV'))?

Sounds like your data comes from somewhere where people use , to separate the integer and fraction parts of a number. Python expects . for that. — user2357112
– user2357112, Commented May 19, 2017 at 20:24

Daniel H · Accepted Answer · 2017-05-19 20:33:49Z

1

Python uses . (period) to separate the integer and fraction parts of a floating-point number, but your data uses , (comma).

To convert to int, you can use value unpacking:

line my_dict = dict(((int(k1), k2), float(v.replace(',', '.'))) for (k1,k2),v in my_dict.iteritems())

Since you’re using Python 2.7, you can also use a dict comprehension to make this simpler:

line my_dict = {(int(k1), k2): float(v.replace(',', '.')) for (k1,k2),v in my_dict.iteritems()}

Bonus:

If you have input from countries other than the US, and you expect you might run into other issues similar to your decimal separation one, you can use the locale module. If you start the script with

import locale
locale.setlocale(locale.LC_ALL, '')

you can use the various functions in the locale module locale.atof) instead of the built-in conversion methods like float, and it will automatically handle the user’s locale settings.

edited May 19, 2017 at 20:33

answered May 19, 2017 at 20:27

Daniel H

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5 Comments

Daniel H Over a year ago

I’ve added mention of the locale module. For simple scripts it’s often overkill, but if you live outside the US or expect a lot of people to use your code, it can be useful.

Daniel H Over a year ago

Somebody downvoted this, and I don’t know why. If there’s a problem with it, could you please explain?

nanika Over a year ago

Using your code I get the same error and I think that now it's because of the period used to separate thousands instead of the comma ValueError: invalid literal for float(): 2.688.44

Daniel H Over a year ago

The sample data you gave doesn’t have thousands separators. If your actual data does, then you’ll need to handle that somehow. It looks like locale.atof supports digit grouping, or you can just .replace it with the empty string, at the cost of breaking if any of the input uses . as a decimal separator.

nanika Over a year ago

Thank you, I resolved using locale.atof ! I don't know why someone downvoted your answer, it's just great!

Ozgur Vatansever · Accepted Answer · 2017-05-19 20:27:19Z

1

>>> float('382,28')
ValueError: invalid literal for float(): 382,28

Because Python expects . for separating the integer and fraction parts of a number. The easiest thing you can do is to replace it:

>>> float('382,28'.replace(",", "."))
382.28

--

my_dict = dict((k, float(v.replace(",", "."))) for k, v in my_dict.iteritems())

answered May 19, 2017 at 20:27

Ozgur Vatansever

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Comments

developer_hatch · Accepted Answer · 2017-05-19 20:27:33Z

1

For the first error, you must change your floats Strings data that looks like, for example "22,32" to "22.32", replace the , for . . For the second question, if you want to get an int from a string, just do int("43") for example.

answered May 19, 2017 at 20:27

developer_hatch

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Comments

Julio Martinich · Accepted Answer · 2018-02-04 21:43:16Z

0

Daniel H already said that in his Bonus answer, but for short I would put the following instruction:

Set locale to spanish, and use locale.atof instead of float.

In code it would be:

import locale
locale.setlocale(locale.LC_NUMERIC,"es_ES")
locale.atof("123,45")

in your case, use

my_dict = dict((k, locale.atof(v)) for k,v in my_dict.iteritems())

instead of

my_dict = dict((k, float(v)) for k,v in my_dict.iteritems())

edited Feb 4, 2018 at 21:43

user555121

answered Feb 4, 2018 at 21:21

Julio Martinich

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