I have a boolean flag that can be None, True, or False. Each value has a different meaning.

I understand the Pythonic way of checking for True and None and not None are:

if bool_flag: 
    print("This will print if bool_flag is True")
    # PEP8 approved method to check for True

if not bool_flag:
    print("This will print if bool_flag is False or None")
    # Also will print if bool_flag is an empty dict, sequence, or numeric 0

if bool_flag is None: 
    print("This will print if bool_flag  is None")

if bool_flag is not None: 
    print("This will print if bool_flag is True or False")
    # Also will print if bool_flag is initialized as anything except None

And if you need to check for all three in an if statement block, you would use a laddered approach, for example:

if bool_flag:
    print("This will print if bool_flag is True")
elif bool_flag is None:
    print("This will print if bool_flag  is None")
else:
    print("This will print if bool_flag is False")
    # Note this will also print in any case where flag_bool is neither True nor None

But what is the Pythonic way of just checking for a value of False when the flag can also be None or True as valid values? I have seen several questions but there doesn’t seem to be a consensus.

Is it “more pythonic” to write:

# Option A:
if isinstance(bool_flag, bool) and not bool_flag:
    print("This will print if bool_flag is False")

# Option B:
if bool_flag is not None and not bool_flag:
    print("This will print if bool_flag is False")

## These two appear to be strictly prohibited by PEP8:
# Option C:
if bool_flag is False:
    print("This will print if bool_flag is False")

# Option D:
if bool_flag == False:
    print("This will print if bool_flag is False")

This topic has been discussed before:

• What is the correct way to check for False?
• In Python how should I test if a variable is None, True or False
• Is there a difference between “== False” and “is not” when checking for an empty string?
• Why does comparing strings using either ‘==’ or ‘is’ sometimes produce a different result?
• Is there a difference between “==” and “is”?

This appears to be the closest answer to my question out of what is available (providing Option A above), but even this Answer is ambiguous (suggesting Option C as well):

• /a/37104262/22396214

However, this answer points out that if not flag_bool is equivalent to if bool(flag_value) == False which would imply that checking for False equivalence using the == operator is the official Pythonic method of checking for False (Option D):

• /a/36936790/22396214

But that directly contradicts this answer that ‘== False’ (Option D) should never be used:

• /a/2021257/22396214