On Mon, 28 Feb 2005 15:50:22 -0500, Dan Sommers wrote:
> The reason their code is so inflexible is that they've filled their
> classes with boiler plate get/set methods.
>
> Why do users of classes need such access anyway? If my class performs
> useful functions and returns useful results, no user of my class should
> care about its attributes. If I "have to" allow access to my attributes
> in order that my users be happy, then I did something else wrong when I
> designed the class and its public interface in the first place.
Consider an interface to a temperature controller. It will
have several properties:
- current temperature (read only)
- target temperature (read/write)
- various tuning parameters that affect the rate of change,
stability, etc.; eg, lookup details on a PID controller
These are properties of the temperature controller object.
In Python these properties are traditionally mapped to attributes.
Under languages that don't have a __getattr__/"property" mechanism
for separating interface from implementation these are implemented
via get/set accessor methods.
It is very often useful to change the temperature setting of
a controller over time. Eg, a chemical protocol might say
"warm from 50 to 80 over a period of 30 minutes, 1 degree
per minute".
In Python that might be written as:
temp_controller = TemperatureController("/dev/com3")
temp_controller.target = 50
print "Bringing reactor to", temp_controller.target
while 1:
print "Current temperature is", temp_controller.current
if abs(temp_controller.current - temp_controller.target) < 0.1:
break
time.sleep(30)
raw_input("Insert sample and press the <enter> key: ")
for temp in range(51, 81):
print "Raising reactor temperature to", temp
temp_controller.target = temp
time.sleep(60)
if abs(temp_controller.current - temp) > 0.1:
print "Variance too high!", temp_controller.current
print "DONE!"
What's wrong with the use of attributes in this case and how
would you write your interface?
Andrew
[EMAIL PROTECTED]
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