Pythonic way of checking null and empty string

Question

I have a simple function that takes 2 params and subtract the first param with the second param.

The function should also do the following:

Check both params are not null, None or empty string
Check both params are numeric
Convert numbers in string into integer (e.g. '7' --> 7)

I am getting errors if empty string is passed in as one of the params. How to write this function in a pythonic way without adding additional checks for empty string?


def get_num_diff(first_num, second_num):
  if ((first_num is not None) & (second_num is not None)):
    if (type(first_num) is str):
      first_num = int(first_num)
    if type(second_num) is str:
      second_num = int(second_num)
    return first_num - second_num
  else:
    return 'NA'

Error:

invalid literal for int() with base 10: ''

try and except works here too. You never checked for empty string. Also use isinstance to check type. — pault
– pault, Commented Jun 25, 2019 at 2:21
There is no such thing as "null" in Python. The closest thing is the None object, but you've listed that separately. — user2357112
– user2357112, Commented Jun 25, 2019 at 2:23

Quinn Mortimer · Accepted Answer · 2019-06-25 02:27:54Z

1

Something like this is better handled using try/except rather than building blocks to handle every case you might encounter.

def get_num_diff(first_num, second_num):
    try:
        first_num = int(first_num)
        second_num = int(second_num)
    except (ValueError, TypeError):
        return 'NA'
    return first_num - second_num

edited Jun 25, 2019 at 2:27

Quinn Mortimer

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answered Jun 25, 2019 at 2:23

James

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1 Comment

Cryssie Over a year ago

Thanks. That makes sense..I was trying to think of ways to capture all cases. This works way better

Evan Bloemer · Accepted Answer · 2019-06-25 02:33:32Z

0

You can check for an empty string with an if statement.

test = ""
if not test:
    print("This test string is empty")

test = "Not Empty"
if test:
    print("This test string is not empty")

Below is example output:

>>> test = ""
>>> if not test:
...     print("This test string is empty")
... 
This test string is empty
>>> test = "Not Empty"
>>> if test:
...     print("This test string is not empty")
... 
This test string is not empty

edited Jun 25, 2019 at 2:33

answered Jun 25, 2019 at 2:25

Evan Bloemer

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2 Comments

pault Over a year ago

Not applicable here since op has numeric values, including possibly 0

Evan Bloemer Over a year ago

It is applicable if OP decides to use it after they check if what is passed is a string.

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