關於python中Enum的個人總結
阿新 • • 發佈:2020-07-01
關於python中Enum的個人總結
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初識
- 可以通過enum模組匯入
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語法
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初始化:
- 可以通過
enum_ = Enum('class_name', names,start = 1)
來建立,其中names可以是字串,可以是列表/元組。內部定義為:
def _create_(cls, class_name, names, *, module=None, qualname=None, type=None, start=1): """Convenience method to create a new Enum class. `names` can be: * A string containing member names, separated either with spaces or commas. Values are incremented by 1 from `start`. * An iterable of member names. Values are incremented by 1 from `start`. * An iterable of (member name, value) pairs. * A mapping of member name -> value pairs. """ metacls = cls.__class__ bases = (cls, ) if type is None else (type, cls) _, first_enum = cls._get_mixins_(bases) classdict = metacls.__prepare__(class_name, bases) # special processing needed for names? if isinstance(names, str): names = names.replace(',', ' ').split() if isinstance(names, (tuple, list)) and names and isinstance(names[0], str): original_names, names = names, [] last_values = [] for count, name in enumerate(original_names): value = first_enum._generate_next_value_(name, start, count, last_values[:]) last_values.append(value) names.append((name, value)) # Here, names is either an iterable of (name, value) or a mapping. for item in names: if isinstance(item, str): member_name, member_value = item, names[item] else: member_name, member_value = item classdict[member_name] = member_value enum_class = metacls.__new__(metacls, class_name, bases, classdict) # TODO: replace the frame hack if a blessed way to know the calling # module is ever developed if module is None: try: module = sys._getframe(2).f_globals['__name__'] except (AttributeError, ValueError, KeyError) as exc: pass if module is None: _make_class_unpicklable(enum_class) else: enum_class.__module__ = module if qualname is not None: enum_class.__qualname__ = qualname return enum_class
通過這樣就可以初始化並返回一個列舉類。
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關於Enum的元素的使用
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通過原始碼可知:可以通過:enum_(value).vlaue/name,或者sth = enum.name-->sth.name/value,至於為什麼,需要檢視原始碼:
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class DynamicClassAttribute: """Route attribute access on a class to __getattr__. This is a descriptor, used to define attributes that act differently when accessed through an instance and through a class. Instance access remains normal, but access to an attribute through a class will be routed to the class's __getattr__ method; this is done by raising AttributeError. This allows one to have properties active on an instance, and have virtual attributes on the class with the same name (see Enum for an example). """ def __init__(self, fget=None, fset=None, fdel=None, doc=None): self.fget = fget self.fset = fset self.fdel = fdel # next two lines make DynamicClassAttribute act the same as property self.__doc__ = doc or fget.__doc__ self.overwrite_doc = doc is None # support for abstract methods self.__isabstractmethod__ = bool(getattr(fget, '__isabstractmethod__', False)) def __get__(self, instance, ownerclass=None): if instance is None: if self.__isabstractmethod__: return self raise AttributeError() elif self.fget is None: raise AttributeError("unreadable attribute") return self.fget(instance) def __set__(self, instance, value): if self.fset is None: raise AttributeError("can't set attribute") self.fset(instance, value) def __delete__(self, instance): if self.fdel is None: raise AttributeError("can't delete attribute") self.fdel(instance) def getter(self, fget): fdoc = fget.__doc__ if self.overwrite_doc else None result = type(self)(fget, self.fset, self.fdel, fdoc or self.__doc__) result.overwrite_doc = self.overwrite_doc return result def setter(self, fset): result = type(self)(self.fget, fset, self.fdel, self.__doc__) result.overwrite_doc = self.overwrite_doc return result def deleter(self, fdel): result = type(self)(self.fget, self.fset, fdel, self.__doc__) result.overwrite_doc = self.overwrite_doc return result
需要先例項化才能使用。
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- 可以通過
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結語
最後,Enum不僅可以是一個好的列舉也可以拿來代替一些繁瑣的類、狀態、順序等東西。比如說:`life = Enum('life', 'born baby teenager adult older die')。
當然,更多的祕密等著你們自己去挖掘。