Overriding True and False ?

Chris Angelico rosuav at gmail.com
Mon Jan 30 02:54:28 EST 2017


On Mon, Jan 30, 2017 at 4:03 PM, Irv Kalb <Irv at furrypants.com> wrote:
> It seems very odd that Python allows you to override the values of True and False.  In the code, True and False were clearly recognized as keywords as they were colored purple.  But there was no error message.
>
> You cannot assign new values to other keywords.  Simple tests of things like:
>
> for = 5
>
> while = 2
>
> not = 3
>
> As expected, all result in SyntaxError: invalid syntax.  Why would Python allow you to override the values of True and False?  I wonder if this is some sort of historical thing as these are the only keywords besides None that are uppercased.  This line:
>
> None = 5
>
> Even gives a special SyntaxError: cannot assign to None

There are slightly different things going on here. Trying to assign to
a piece of syntax like "while" makes absolutely no sense, but trying
to assign to "None" is structurally sane, yet disallowed. IIRC there's
only one non-assignable name in Python 2 (None), but as mentioned,
Python 3 adds True and False to that. (Interestingly, Ellipsis is not
included in that.)

> I teach intro to programming using Python.

May I please request that you consider teaching Python 3? Python 2
isn't going anywhere (for better or for worse), and Py3 is a superior
language in many ways, not least of which is that it keeps text and
bytes separate, giving text the full power that it should have. For a
beginning programmer, this is very helpful; there's nothing to
un-learn when going international. (There will be new nuances to be
learned, such as RTL text, but nothing to unlearn.) Python 3 also
fixes a number of other problems that Python 2 inherited from C,
making it altogether a better language for teaching with.

ChrisA


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