Constants in Python

[Brent W. Hughes]

Warning: Newbie at work!

I was planning to write some code something like this:

class CTree:
LEAFSIZE = 4
LeafNode = [None] * LEAFSIZE
KEY,DATA,LEFT,RIGHT = range(LEAFSIZE)
#---------------------------------------------------
def Add(self,Node,SubTree):
Key1 = Node[KEY]
....

But then I realized that the last line (and many more similar lines)
would probably need to be writen thusly:

Key1 = Node[CTree.KEY]

I find this a little ugly, not to mention more typing. I suppose
I could move these lines:

LEAFSIZE = 4
KEY,DATA,LEFT,RIGHT = range(LEAFSIZE)

out of the class and make them global, but this kind of runs
against the grain.

Is there another way to deal with "constants"?

 

[Andrew Koenig]

I was planning to write some code something like this:

class CTree:
LEAFSIZE = 4
LeafNode = [None] * LEAFSIZE
KEY,DATA,LEFT,RIGHT = range(LEAFSIZE)
#---------------------------------------------------
def Add(self,Node,SubTree):
Key1 = Node[KEY]

But then I realized that the last line (and many more similar lines)
would probably need to be writen thusly:

Key1 = Node[CTree.KEY]

How about this?

Key1 = Node[self.KEY]

Seems consistent with other class-relative usages.

 

[John Lenton]

Warning: Newbie at work!

I was planning to write some code something like this:

class CTree:
LEAFSIZE = 4
LeafNode = [None] * LEAFSIZE
KEY,DATA,LEFT,RIGHT = range(LEAFSIZE)
#---------------------------------------------------
def Add(self,Node,SubTree):
Key1 = Node[KEY]
...

But then I realized that the last line (and many more similar lines)
would probably need to be writen thusly:

Key1 = Node[CTree.KEY]

I find this a little ugly, not to mention more typing. I suppose
I could move these lines:

LEAFSIZE = 4
KEY,DATA,LEFT,RIGHT = range(LEAFSIZE)

out of the class and make them global, but this kind of runs
against the grain.

Is there another way to deal with "constants"?

not as far as I know. I'm just posting to underline what Andrew just
said: you want to do self.KEY, not CTree.KEY; the latter is a disaster
from a code reusability standpoint, because you just rendered your
class unsubclassable. Well, not quite, but you certainly restricted it
a lot.

--
John Lenton ([email protected]) -- Random fortune:
Deliver yesterday, code today, think tomorrow.

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