[Tutor] diferent between " "(empty string) and None as condition

[DL Neil]

On 24/04/20 7:06 AM, Emin Kovac wrote:
> pasword = ""
> while not pasword:
> pasword = input ('Pasword: ')
> 
> username = None
> while not username:
> username = input('Username: ')
> My question is when should I or what is better to use as
> condition empty string (" ") or None?
> Anyway, what is different between an empty string and None


Here's an exercise to try:

 >>> value = input( "what? " )
what?		# don't type anything, press the Enter key
 >>> value
''
 >>> type(value)
# what is the response here?


When the 'username' while-loop executes for the first time, what will be 
the value and type of username?

When the 'Enter-key only' value is evaluated, what is its type and value?

So, when the 'username' while-loop is executed for the second time, will 
it have the same type as before?

Does that help make your own decision about which is better (in this 
situation)?


NB I like to finish the "input-prompt" with a question-mark (assuming 
English-language users!) because it 'prompts' the user to understand 
that (s)he should enter a value...


Complicating the issue is the question of which type-value combinations 
will auto-magically convert to Boolean-type - and whether as True or as 
False. This you may already understand and is thus part of your enquiry. 
If not, a recommended reading topic!


Beware of either a typo or a misunderstanding (see above):

<<<...empty string (" ")>>>

what appears within the quotation marks is a "Space" character - we 
can't see it, but it is very definitely there! Thus, Space is 
considerably different to "" which 'contains' no characters at all and 
is known as the Nulstring or "empty string"!

With my aging eyes, I rarely use either as "literal constants" inside my 
active-code, simply because it is so easy to quickly mis-read! Instead, 
'at the top' I declare 'constants' (in Python this is a convention 
rather than a rule), eg

NULSTRING = ""
SPACE = " "

thereafter, my code is easier-on-the-eyes, if long-winded/pedantic, eg

pasword = NULSTRING

or, if you prefer

password = NULL_STRING


PS further eye-distractive criticism because the single "L" harks back 
to even before ASCII code 000 (called "NUL"), but the English 
word/spelling is "null". My guess is you will want to stop there - 
people with a desire for technical-precision can really 'go to town' on 
these distinctions...


My preference is to use None when at a stage where the value is 
completely unknown (or irrelevant), eg an optional parameter for a 
function. Whereas NULSTRING (or 0, or False, ...) indicates that we 
'know' the value and that it has a definite meaning and purpose.
-- 
Regards =dn