Eiffel better than Python ?

[D-Man]

On Tue, Jul 03, 2001 at 09:32:06PM +0000, Dublanc, David wrote:
| What is exactly weak typing ? 

Weak typing is what the shell or perl do : anything can be used
anywhere and it only has the type "variable" (or whatever you want to
call it).  Something like the following :

#!/usr/bin/perl
print 2     + "1"  ;
print 2     + "1a" ;
print "1"   + "2"  ;
print "1a"  + "2"  ;
print "1"   + 2    ;
print "1a"  +  2   ;


What you get is an interesting auto-coercion between strings and
integers because there is no difference, as far as perl is concerned.
Some of those, in Python, would be type errors :

>>> print 2 + "1"
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
TypeError: unsupported operand types for +
>>>

The closest thing that might work in Python would be

>>> print 2 + int( "1" )
3
>>>

but it doesn't always work (as it does in Perl) :

>>> print 2 + int( "1a" )
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
ValueError: invalid literal for int(): 1a
>>>

Another indication that perl has weak typing is the following behavior :

$ perl
print $undefined_variable_name + 10 ;
10
$

In perl if a variable doesn't exist, and it is used in numerical
context it is treated as 0, or as the empty string if used in string
context.  In Python that would raise a NameError exception.

| I believed that Python was weak typing !

As you can see above, Python actually checks the types to ensure that
they are sane for the given operation.  It checks them _dynamically_
(at run time) as opposed to statically (at compile time).

There are 4 forms of type checking :

weak
strong
dynamic
static

Some people mistakenly consider dynamic == weak and static == strong,
but they are 2 different axis.

HTH,
-D