OT: Crazy Programming

[Andrew Dalke]

Chris:
> Peter Hansen <peter at engcorp.com> wrote:
  ...
>> Is it just a gut feeling, or do you really have specific examples on
>> which you base these claims?
>
>Well, in writing Perl modules I could continue to use(to access a data
>member of an object, stored as a hash):
  ..
>And use this as:
>
>   print $guy->name("John");
>
>Or, I could try out lvalue subroutines and use something like:
>
  ..
>   print $guy->name="John";

That still follows under "gut feeling" since Python has almost
identical mechanisms, and then some, so your "specific example"
is actually a counter example since there are more ways to do it
in Python.  (I could also add __setattribute__ to the mix.)

# NOTE: I consider this to be an ugly style and advise people
# they they shouldn't use it.  I write it to make it similar to
# the Perl code.
class Person:
  def name(self, name = None):
    if name is not None:
      self.name = name
    return self.name

print guy.name("John")

# This is much more typical Python
class Person:
  def __init__(self, name = None):
    self.name = name

guy = Person()
guy.name = "John"
print guy.name

# This reimplements the attribute lookup using the older-style
# __getattr__/__setattr__ hooks.
class Person:
  def __init__(self, name = None):
    self._name = name
  def __getattr__(self, key):
    if key == "name":
       return self._name
    return getattr(self, key)
  def __setattr__(self, key, value):
    if key == "name":
       if value == "":
         raise TypeError("Name must have at least one letter")
       self._name = value
       return
    self.__dict__[key] = value

guy = Person()
guy.name = "John"
print guy.name


# This is a new (2.2) way to implement attribute lookup
class Person(object):
  def _getName(self):
    return self._name
  def _setName(self, val):
    if val == "":
      raise TypeError("Name must have at least one letter")
    self._name = val
  name = property(_getName, _setName)

>>> p = Person()
>>> p.name = "John"
>>> print p.name
John
>>> p.name = ""
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
  File "<stdin>", line 6, in _setName
TypeError: Name must have at least one letter
>>>

                    Andrew
                    dalke at dalkescientific.com