At 08:17 PM 1/26/2011, Chris wrote:
I have a class (A, for instance) that possesses a boolean (A.b, for
instance) that is liable to change over an instance's lifetime.
Many of the methods of this class (A.foo, for instance) should not
execute as long as this boolean is false, but should instead raise an
exception.
Can I use a decorator to implement this functionality? More exactly,
could I define a function called 'checker' that accomplishes this:
Mark Summerfield's book "Programming in Python 3" has an example
something like this (p.357) called 'positive_result'. I hesitate to
quote the entire thing, so I'll quote only the inner 'half' of the decorator:
def wrapper(*args, **kwargs):
result = function(*args, **kwargs)
assert result >= 0, function.__name__ + "() result isn't >= 0"
return result
I would guess you would have to count on the first item in the
methods' args to be self, and use that to test whether your attribute
is false/true?
Mark?
def checker(f):
...
class A():
b = True
@checker
def foo(self,...):
print 'in foo'
a = A()
a.foo()
a.b = False
a.foo()
would result in:
'in foo'
Exception: ...
This exact solution isn't necessary, just something that doesn't
require me to have the clunky:
def foo(self,...):
if self.b:
...
else: raise Exception('b attribute must be true before executing
this method')
in every method.
Thanks,
Chris
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