Che M wrote:
This is another very basic structural question, related to one I asked last
week, and again is not necessarily germane only to Python.
Let's say you have a sequence of two calculations or manipulations you need to do, each
one done as a function called by an overall calculate_something() function. The
"answer" to each function is then used in the next function. I can think of
two ways to make that answer available for use in the next function: 1) pass it in, or
2) declare it as self.answer and then it is available to the whole class instance.
What are the dis/advantages to these two different ways? Here are examples,
with only the overall calculate_something() function shown:
1.Pass the variable to the second function.
def calculate_something(self):
answer = self.do_first_calculation() #1st function returns answer
self.do_second_calculation(answer) #2nd is passed answer and uses it.
2. Create the variable in the class instance scope and use that in the second
function.
def calculate_something(self):
self.do_first_calculation() #1st function creates
self.answer
self.do_second_calculation() #2nd uses self.answer
Both of these approaches can work, but I would like to better understand when
it is best to do one or the other. Obviously if I know I will need to make
self.answer available for use by other functions, I would want to choose (2).
But what other considerations should I, well, consider?
Thanks,
Che
You call these functions, but since you have the "self" argument, I'll
assume it's a method instead.
use #2 only if the "answer" is relevant for further operations, AND (is
time-consuming to calculate compared to the memory consumed by storing
it, OR if calculating it has side effects)
prefer #1 because:
it doesn't take up space in the object
it goes away when the particular method ends, not when the object
is destroyed (rule -- the sooner the better)
it doesn't clutter the namespace of the class
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