Check if multiple variables are not None in Python

Check if multiple variables are not None in Python #

To check if multiple variables are not None:

1. Wrap the variables in a list.
2. Use a generator expression to iterate over the list.
3. On each iteration, check if the current list item is not None.
4. Pass the generator object to the all() function.

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a = 'a'
b = 'b'
c = 'c'

if all(item is not None for item in [a, b, c]):
    print('Multiple variables are NOT None')
else:
    print('At least one of the variables stores a None value')

We used square brackets to add the variables to a list and used a generator expression to iterate over the list.

On each iteration, we check if the current list item is not None and return the result.

The last step is to pass the generator object to the all() function.

The all() built-in function takes an iterable as an argument and returns True if all elements of the iterable are truthy (or the iterable is empty).

An alternative approach is to use the in operator.

To check if multiple variables are not None:

1. Wrap the variables in a sequence (e.g. a tuple or a list).
2. Use the not in operator to check if None is not a member of the sequence.
3. If the sequence doesn't contain None, then the variables are not None.

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a = 'a'
b = 'b'
c = 'c'

if None not in (a, b, c):
    # 👇️ this runs
    print('Multiple variables are NOT None')

This approach looks much simpler than the previous one. However, the in and not in operators check for equality, e.g. None != a, None != b, etc.

This is not a good practice in Python, as it is recommended to check for None using the is keyword.

The in operator tests for membership. For example, x in l evaluates to True if x is a member of l, otherwise it evaluates to False.

x not in l returns the negation of x in l.

An alternative approach is to use the and operator multiple times.

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a = 'a'
b = 'b'
c = 'c'

if a is not None and b is not None and c is not None:
    print('Multiple variables are NOT None')

This is generally not recommended, as it is quite repetitive and hard to read.

The expression x and y returns the value to the left if it's falsy, otherwise the value to the right is returned.

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result = False and 'hello'
print(result)  # 👉️ False

All values that are not truthy are considered falsy. The falsy values in Python are:

• constants defined to be falsy: None and False.
• 0 (zero) of any numeric type
• empty sequences and collections: "" (empty string), () (empty tuple), [] (empty list), {} (empty dictionary), set() (empty set), range(0) (empty range).

So if the value to the left is any of the aforementioned falsy values, the value to the left is returned.

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a = 'a'
b = 'b'
c = 'c'

if all(item is not None for item in [a, b, c]):
    print('Multiple variables are NOT None')
else:
    print('At least one of the variables stores a None value')