bool() vs is not None

Question

I have two functions that return a bool. The first is using bool() and the second is using is not None.

def func_1(x) -> bool:
    return bool(x)

def func_2(x) -> bool:
    return x is not None

foo = "something"
bar = None

print(func_1(foo))
print(func_2(foo))
print("-----")
print(func_1(bar))
print(func_2(bar))

Here is the output

True
True
-----
False
False

Is there a difference between is not None and bool() in this instance? Is there something I may want to consider when using one or the other?

Answer 1

Is there a difference between is not None and bool() in this instance?

Yes! Check the Python documentation here, you will find that some values are falsey even beeing different from None.

---

Just as an example:

>>> 0 != None
True
>>> bool(0)
False

Answer 2

Here's the effect of bool on various types (not comprehensive):

• numeric types: False if 0, True otherwise
• sequence type (list, tuple, etc): False if empty, True otherwise
• object: False if None, true otherwise

(Note that if None is assigned to a variable that previously referred to a sequence type, the semantics will change from 2nd to 3rd bullet above).

Here's the effect of is not None:

• variable assigned to be None: False
• other: True

Answer 3

According to this site, using bool function, all following will return False :

1. None
2. False
3. Zero
4. Operators...