On 2017-10-01 01:07, Bill wrote:
Steve D'Aprano wrote:
On Sun, 1 Oct 2017 08:47 am, Bill wrote:
I spent a few hours experimenting with @property. To my mind it seems
like it would be preferable to just define (override) instance methods
__get__(), __set__(), and possibly __del__(), as desired, as I could
easily provide them with "ideal" customization. Am I overlooking something?
Probably.
You and Ned are both right. Up until a few minutes ago, I wasn't
thinking about a class having more than 1 attribute that I wanted to
change. And now I realize that __get__ doesn't really make sense in
that context (in the back of my mind was the notion that @property
defined __get__, __set__ and __del__) and I allowed that to obscure my
vision. I was on the verge of giving up anything to do with computers,
forever. : )
BTW, your example (below) is very nice! I may have seen something
similar before, but I am starting to appreciate it better now. I think
all of this would have made a bit more sense (to me), if instead of just
"@property", the syntax was "@property.getter". Now I am forced to ask
the question, why did they use the underscore (on temperature) in the
example on the bottom of this page? Is one forced to introduce new
identifiers in order to define a setter?
https://www.programiz.com/python-programming/property
self._temperature is where the value is actually stored.
Suppose you had this instead:
@temperature.setter
def temperature(self, value):
if value < -273:
raise ValueError("Temperature below -273 is not possible")
print("Setting value")
self.temperature = value # <-- changed this line
What would happen when you tried to set the temperature?
Because of the last line, the setter would be calling itself recursively
until it hit the maximum stack depth.
A leading underscore is the normal convention to indicate that it should
be treated as "private".
If you wanted the temperature to be read-only, you'd make the value
"private" and have a getter but not a setter.
[snip]
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