while c = f.read(1)

Magnus Lycka lycka at carmen.se
Mon Aug 22 16:39:45 CEST 2005


Antoon Pardon wrote:
>>Python doesn't guess. There are a range of values that will be treated, 
>>in a Boolean context (how perlish) as equivalent to False.
> 
> Yes it does. 

No it doesn't!

> Python has no way to know what would be the most
> usefull Boolean interpretation of these values in a particular
> context.

It's hardly the task of the interpreter to try to do that.

> That it picks one out is guessing. 

No, it simply follows a well defined specification.
See http://docs.python.org/ref/Booleans.html
There is no guessing involved in that.

> Lisp imterprets
> an empty list as false, scheme interprets it as true. So
> both seem usable interpretations.

You might argue that *Guido* was guessing when he decided what
the most useful behaviour of Python would be in this case, and
there's probably some truth in that, just as there is some
guesswork involved in most programming language design decisions,
but that's another thing. That's not Python guessing, it's
Guido using his excellent lanugage design skills. It seems most
Python programmers agree that he "guessed" right here, as usual.

(Perhaps you thought that "Python" was the name of the language
designer. It's not. Python's design is led by Guido van Rossum,
and the name Python comes from a (mostly) British comedy group.)

You might also argue that this behaviour is counter to the
Python dogma of "explicit is better than implicit". Python also
allows you to get a float out of an expression such as "2*3.1"
without forcing an explicit cast, as in "float(2)*3.1".

You should note that the first Python tenet is "Beautiful is
better than ugly" and that's probably what we have to blame here.

There seems to be close to a consensus, that "if users:" is more
beautiful than e.g. "if len(users) > 0:" or
"if (len(users)==0)==False" or for that matter
"if ((len(users)==0)==False)==True" or
"if (((len(users)==0)==False)==True)==True" etc.

What's true and false for Python, belongs to the few things you
actually have to learn, and I can appreciate that it's annoying
for a frequent schemer to remember that it's not the same in
Python, but it seems that very few people argue with the way
Python behaves in this respect.



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