(Python) Make variable equal to zero if the data type is not numeric

Question

I have this variable assignation in my code which take data from web and converts it to float (after extracting numbers only)

variable_1 = float(re.sub('[^0-9]','', basic_data_list[17]))

Now if there is no data on the web (which is specified by "-") I get the error

ValueError: could not convert string to float: which is expected.

Is there any way I can get the value zero assigned to this variable if no data is available? Is there any equivalent of Excels's IsError in python?

you can check first if the data is "-". – Shiping Feb 25 '17 at 16:25 — Shiping, Feb 25 '17 at 16:25

Eric Duminil · Accepted Answer · 2017-02-25T16:36:02.987

3

First, for a float, you probably should accept . and - :

variable_1 = float(re.sub('[^0-9\-\.]','', basic_data_list[17]))

Otherwise :

float(re.sub('[^0-9]','', '-3.5'))

would return

35.0

Then :

variable_1 = float(re.sub('[^0-9\-\.]','', 'abc'))

raises a ValueError.

You could use a try block. There's even an example in the documentation which directly describes your problem :

>>> while True:
...     try:
...         x = int(raw_input("Please enter a number: "))
...         break
...     except ValueError:
...         print "Oops!  That was no valid number.  Try again..."

In the except ValueError part, you could define variable_1 as you wish. Note that 0 is not always the best value to assign for "not a number" :

try:
  variable_1 = float(re.sub('[^0-9\-\.]','', basic_data_list[17]))
except ValueError:
  variable_1 = 0.0

edited Feb 25 '17 at 16:36

answered Feb 25 '17 at 16:23

Eric Duminil

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See update. Just set `variable_1 = 0` in the `except` block. – Eric Duminil Feb 25 '17 at 16:31
See @antonmik answer. It's a one-liner, but it's not very readable IMHO. – Eric Duminil Feb 25 '17 at 16:32
Thank you! That was helpful – Stelios Feb 25 '17 at 16:41

score 2 · Answer 2 · edited May 23 '17 at 12:25

2

str.isnumeric() works on unicode strings. so if you use:

unicode(basic_data_list[17]).isnumeric()

you'll get a boolean value - True for numeric and False for non-numeric values.

so i'm thinking something along these lines will work:

variable_1 = float(re.sub('[^0-9]','', basic_data_list[17] if unicode(basic_data_list[17]).isnumeric() else "0"))

from your reply i'm guessing youre using python 3. heres what i found: NameError: global name 'unicode' is not defined - in Python 3

you should be able to use this by replacing "unicode" with "str"

edited May 23 '17 at 12:25

Community

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answered Feb 25 '17 at 16:30

antonmik

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It gives error -NameError: name 'unicode' is not defined – Stelios Feb 25 '17 at 16:35
You are right. I am using Python 3.6. Its works fine now. Thanks a lot to you too. – Stelios Feb 25 '17 at 16:46

(Python) Make variable equal to zero if the data type is not numeric

2 Answers2