anything like C++ references?

[Bengt Richter]

On Mon, 14 Jul 2003 16:44:09 -0700, Tom Plunket <tomas at fancy.org> wrote:

>Noah wrote:
>
>> As others have explained, you just return the value.
>> It's just a different point of view. Instead of
>>     change (v)
>> you have:
>>     v = change (v)
>
>Ahh, now I remember what I wanted to do, and you're right- it's
>more verbose and didn't really seem to add anything.  I wanted to
>in-place clamp integers in a range, or maybe they were even
>member variables;
>
>def Color:
>   def SomeOperation():
>      # modify self.r, g, b
>      self.r = clamp(self.r, 0, 255)
>      self.g = clamp(self.g, 0, 255)
>      self.b = clamp(self.b, 0, 255)
>
>...that was just more typing than I wanted at that point,
>although I'm sure that the keystrokes I burned were more than
>made up for by Python's allowing me to do:
>
>   def clamp(val, lowVal, highVal):
>      if (lowVal <= val <= highVal):
>         return val
>
Doesn't clamping ususally return the limit values when exceeded?
E.g.,

    def clamp(val, lowVal, highVal): return max(lowVal, min(val, highVal))

Also, if you are dealing with member variables, you can clamp them whenever
they are set (including via __init__ code ;-), e.g., (here I built in the
clamping code and constants, though it might make sense to parameterize the
limits in generating a class or subclass for instances that are all to be
clamped the same):

 >>> class RGB(object):
 ...     def __init__(self, r=0, g=0, b=0): self.r=r; self.g=g; self.b=b
 ...     def __setattr__(self, name, val):
 ...         if name in ('r', 'g', 'b'): object.__setattr__(self, name, max(0, min(val, 255)))
 ...         else: object.__setattr__(self, name, val)
 ...     def __repr__(self): # just so we can see easily
 ...         return '<RGB instance (%s, %s, %s) at 0x%x>' % (self.r, self.g, self.b, id(self))
 ...
 >>> o = RGB(-3,22,512)
 >>> o
 <RGB instance (0, 22, 255) at 0x7d8e10>
 >>> o.g = 256
 >>> o
 <RGB instance (0, 255, 255) at 0x7d8e10>
 >>> o.b = -1
 >>> o
 <RGB instance (0, 255, 0) at 0x7d8e10>
 >>> o.r, o.g, o.b
 (0, 255, 0)
 >>> o.g
 255
 >>> o.other = 'not clamped'
 >>> o
 <RGB instance (0, 255, 0) at 0x7d8e10>
 >>> o.other
 'not clamped'

(Of course, you wouldn't want to use this kind of RGB object to represent pixels
where you had to process a lot of them fast ;-)

Regards,
Bengt Richter