This is roughly what I had in mind:
[Everything is fake here, to only thing that is supposed to be
illustrated is how assumptions get cleared up when their objects
vanish.]
import weakref
class Assumption(object):
pass
class AssumePositive(Assumption):
def __init__(self, x):
self.var = weakref.ref(x, self.cb)
def cb(self, var):
if self.callback:
self.callback(self)
def __str__(self):
return str(self.var) + ' > 0'
class Symbol(object):
def __init__(self, name):
self.name = name
def __str__(self):
return str(self.name)
assumptions = {}
def remove_assumption(wr):
print 'removing assumption', assumptions[wr]
del assumptions[wr]
N = 0
def assume(a):
global N
print 'adding assumption', a, 'as', N
assumptions[a] = N
a.callback = remove_assumption
N += 1
def test2():
x = Symbol('y')
assume(AssumePositive(x))
print assumptions
print 'leaving test2'
def test():
x = Symbol('x')
assume(AssumePositive(x))
print assumptions
print 'entering test2'
test2()
print assumptions
print 'leaving test'
test()
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