What is the difference between None and boolean (True, False) in python's default argument values?

user_9828197 0
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In function definitions, one can define a boolean default argument's values as argument=None or argument=False.

An example from pandas concat:

def concat(
    objs,
    axis=0,
    join="outer",
    join_axes=None,
    ignore_index=False,
    keys=None,
    levels=None,
    names=None,
    verify_integrity=False,
    sort=None,
    copy=True,
):

While both usages can be found, why would one be using one over the other?

Is there any PEP on this?

python
4 Answers

True and False are specific bool values. Use default False when you have a bool field and you want the default to be False.Don't use False as a value for a non-bool field.

None is used as a generic placeholder when the value will be set later. It can be typed as Optional[T], which is equivalent to Union[T, None].

You might be thinking of None and False as similar because they're both "falsy" (bool(x) returns False), but the same is true of several other values, [] () {} 0 0.0, etc and we don't use them like None either.

In your example, True/False are used where the field takes a boolean value. None is used where the field takes an Optional[List]. (The exception is sort: Optional[bool], which is being used temporarily as an ad-hoc compatibility tool for a deprecated behavior.)

user_120553830

True and False are boolean values, so in this context None can make sense if you have a boolean variable that can be in an 'unknown' state. Strictly spoken, such a variable would not be boolean, but in reality, this can be quite handy.

For example:

# In the beginning, we simply don't know if it's true or not
is_cat_alive = None

# But later we will determine the status
is_cat_alive = check_cat_in(box)

Note that if you are using a boolean like this, then if is_cat_alive will be false when is_cat_alive is either False or None which makes sense but might not be what you want to know. So to explicitly check for a dead cat, you would have to use if is_cat_alive == False.

user_48509490

None is similar to a null value if you know anything about those. Someone might say it's equal to 0, but None means that it is nothing. Say age = None for example. age is a variable, but it is equal to nothing. False is an actual value. True and False can be used as an indicator such as

def name_check(name)
    if name == "Brittany":
        return True
    else:
        return False

Calling that function with "Brittany" as the name parameter would return True which could be used in other conditions as well. Hope this helped! Good luck!

user_120278220

Look at the following code:

my_string = ''
my_other_string = None
my_final_string = 'I am a string'

If you were using these within python in something like an if statement they would actually equal the following:

my_string = False
my_other_string = None
my_final_string = True

Hope that helps

user_118338990
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