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from abc import ABCMeta, abstractmethod
from collections import OrderedDict
from contextvars import ContextVar, Token
from copy import deepcopy
from typing import List, Optional, ContextManager, Any
from public import public
@public
class Action(object):
"""An Action."""
inside: bool
def __init__(self):
self.inside = False
def __enter__(self):
getcontext().enter_action(self)
self.inside = True
return self
def __exit__(self, exc_type, exc_val, exc_tb):
getcontext().exit_action(self)
self.inside = False
class Tree(OrderedDict):
def walk_get(self, path: List) -> Any:
if len(path) == 0:
return self
value = self[path[0]]
if isinstance(value, Tree):
return value.walk_get(path[1:])
elif len(path) == 1:
return value
else:
raise ValueError
@public
class Context(object):
__metaclass__ = ABCMeta
@abstractmethod
def enter_action(self, action: Action):
...
@abstractmethod
def exit_action(self, action: Action):
...
def __str__(self):
return self.__class__.__name__
@public
class NullContext(Context):
"""A context that does not trace any actions."""
def enter_action(self, action: Action):
pass
def exit_action(self, action: Action):
pass
@public
class DefaultContext(Context):
"""A context that traces executions of actions."""
actions: Tree
current: List[Action]
def enter_action(self, action: Action):
self.actions.walk_get(self.current)[action] = Tree()
self.current.append(action)
def exit_action(self, action: Action):
if self.current[-1] != action:
raise ValueError
self.current.pop()
def __init__(self):
self.actions = Tree()
self.current = []
def __repr__(self):
return f"{self.__class__.__name__}({self.actions}, current={self.current})"
_actual_context: ContextVar[Context] = ContextVar("operational_context", default=NullContext())
class _ContextManager(object):
def __init__(self, new_context):
self.new_context = deepcopy(new_context)
def __enter__(self) -> Context:
self.token = setcontext(self.new_context)
return self.new_context
def __exit__(self, t, v, tb):
resetcontext(self.token)
@public
def getcontext() -> Context:
"""Get the current thread/task context."""
return _actual_context.get()
@public
def setcontext(ctx: Context) -> Token:
"""
Set the current thread/task context.
:param ctx: A context to set.
:return: A token to restore previous context.
"""
return _actual_context.set(ctx)
@public
def resetcontext(token: Token):
"""
Reset the context to a previous value.
:param token: A token to restore.
"""
_actual_context.reset(token)
@public
def local(ctx: Optional[Context] = None) -> ContextManager:
"""
Use a local context.
:param ctx: If none, current context is copied.
:return: A context manager.
"""
if ctx is None:
ctx = getcontext()
return _ContextManager(ctx)
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