0_context-tool.md

python context sample

context-tool.py

import contextlib
import copy


class Context(object):

    def __init__(self, init_state={}):
        self._states = [init_state]

    @property
    def state(self):
        return self._states[-1]

    @contextlib.contextmanager
    def push(self, new_state):

        state = copy.copy(self.state)
        state.update(new_state)
        self._states.append(state)
        yield self
        self._states.pop()

c = Context({'a':'AA', 'c': ['ccc']})
s1 = c.state


with c.push({'b': 'BB', 'a': 'AAA'}) as cc:
    #assert id(cc.state['c'], s1['c'])
    s2 = cc.state
    print s1['c'], id(s1['c'])
    print s2['c'], id(s2['c'])
    assert id(s1['c']) == id(s2['c'])
    print s2
print cc.state