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Perl is worse! (was: Python is Wierd!)

Chris Lawrence quango at watervalley.net
Fri Jul 28 00:42:17 EDT 2000 
On Fri, 28 Jul 2000 03:29:06 GMT, Steve Lamb <grey at despair.rpglink.com> wrote:
>    None could be converted into an empty list.  None is nothing.  I fail to
>see how you can't populate a list with a single nothing.

Reasonable enough.  Though you're not populating a list with a single
nothing; you're making an empty list.  OTOH, by the logic below, why
not [None] instead of []?

>    1 is a single value.  I fail to see why that cannot be converted to [1]
>which is allowed, btw. 
>a = [1]
>a
>
>    123 is a single value.  I fail to see why that cannot be converted to
>[123] which, again, is allowed.  See above.

Not sure about these.  If you want a one-element list, say so.  x =
[1] is concise.  x = list(1) ain't.  If [] offends your sensibilities,
try x = list(1,).

>    "abc" could either be a single value or a sequence.  It is converted as
>["a", "b", "c"].  Of course, the same /could/ be said for the above.  However,
>let's play around with this one since it is the only one that works somewhat
>as expected in conversion.

"abc" is a string.  Strings are immutable sequences in Python.
list((1,2,3)) = [1,2,3].  Same principle.

>a = "abc"
>a
>a = list(a)
>a = str(a)
>a
>
>    a is now "['a', 'b', 'c']".  Which means we split a string up when
>converting to list but don't concatinate on the way back.  I'd think, then,
>that we'd not split the string up in the first place and consider it a single
>value for a single entry in a list.  IE, ["abc"].  But, of course, dropping
>back from a list to a str isn't perfect since you're going from a more complex
>structure into a simple data set.

How does Python know you want "['a','b','c']" instead of "['abc']"?
(And wouldn't you *really* expect "abc"?)  It can't.  But logic
suggests that ['aa', 'b', 'c'] isn't the same thing as ['a', 'a', 'b',
'c'], yet your representation would say they are the same.

This strikes me as type-based magic, which Python tries to avoid.

>    How did I run across this?  Because I wanted to create an empty name each
>time a class instance is created.  Since I was building the class I didn't
>know if I was going to use a list or a str.  I figure I could just set it
>to None and then manipulate it later.  Nope.  Couldn't even convert it even
>though the conversion seems quite straightforward to me.  None into any
>structure should yield and empty of that structure.  We can have empty
>strings, tuples, lists and directories.  Funny thing, though.  I can do this
>and it works just fine:

Huh?  Python is a strongly typed language.  None is an instance (the
sole instance, natch) of a NoneType variable.  Should NoneType things
transmute themselves into other types of things at the drop of a hat?
This sounds fishily like Perlish automagic conversion.

>    However, if we want to create the namespace with nothing we cannot because
>we cannot convert it for later use.  Thus, we are back to declaring variables
>except this time we're doing it with automagical (implicit) means instead of
>explicit.  

Sure you can.

x = None
...
for y in range(10):
  if x is not None:
     x = x + y
  else:
     x = y

Which begs the question: why would you want to declare a variable
without knowing what you're going to stick in it?

(Incidentally, you're not creating a namespace, you're making an entry
in a particular namespace...)

>    I just don't understand how people can advocate for types and the
>restrictions they impose while, on the other hand, embracing a language that
>is free enough to shoot yourself in the foot by reassigning None.

Hmm, works in JPython too.  And Python 2.0b1.  Maybe it's a feature ;-)

Frankly, I don't know how you'd get None back.  And it will play havoc
with things:

None = 1
if None:
  print 'Hello'

I suspect Guido will tell you, "don't do that." ;-)


Chris
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