1.Field類簡介

①Field物件指明瞭每個欄位的元資料（任何元資料），Field物件接受的值沒有任何限制

②設定Field物件的主要目就是在一個地方定義好所有的元資料

③注意，宣告item的Field物件，並沒有被賦值成class屬性。（可通過item.fields進行訪問）

④Field類僅是內建字典類（dict）的一個別名，並沒有提供額外的方法和屬性。被用來基於類屬性的方法來支援item生命語法。

【Field類原始碼】

class Field(dict):
    """Container of field metadata"""

2.dict類原始碼剖析

類內部方法

class dict(object):
    """
    dict() -> 建立空字典
    dict(mapping)  -> 從對映物件的鍵值對中初始化新字典{"key":value}
    dict(iterable) -> 從迭代器初始化字典 d[key] = value
    dict(**kwargs) -> 使用字典初始化新字典
    """
	
	# 1.清除字典內部所有內容 -> 空字典
    def clear(self):
        pass

	# 2.字典dict的複製
    def copy(self):
        """ dict_copy = D.copy()"""
        pass

	# 3.靜態方法。返回一個新的字典，其中包含來自迭代器的鍵，以及對應的值
    @staticmethod # known case
    def fromkeys(*args, **kwargs): # real signature unknown
        pass

	# 4.返回指定鍵k的值，如果值不在字典中返回d的值
    def get(self, k, d=None): # real signature unknown; restored from __doc__
        pass

	# 5.以字典形式返回可遍歷的(鍵，值)對
    def items(self): # real signature unknown; restored from __doc__
        pass

	# 6.以列表形式返回一個字典所有的鍵
    def keys(self): # real signature unknown; restored from __doc__
        pass
		
	# 7.刪除字典給定鍵k所對應的值，返回值為被刪除的值。k值必須給出。否則，返回d值。
    def pop(self, k, d=None): # real signature unknown; restored from __doc__
        pass

	# 8.隨機返回並刪除字典中的一對鍵和值
    def popitem(self): # real signature unknown; restored from __doc__
        pass

		
	# 9.和get()類似, 但如果鍵k不存在於字典中，將會新增鍵並將值設為d
    def setdefault(self, k, d=None): # real signature unknown; restored from __doc__
        pass

	# 10.將字典2中的鍵值對更新入呼叫字典中
    def update(self, E=None, **F): # known special case of dict.update
        """
        If E is present and has a .keys() method, then does:  for k in E: D[k] = E[k]
        If E is present and lacks a .keys() method, then does:  for k, v in E: D[k] = v
        In either case, this is followed by: for k in F:  D[k] = F[k]
        """
        pass

	# 11.以字典的形式返回字典中所有的值
    def values(self): # real signature unknown; restored from __doc__
        """ D.values() -> an object providing a view on D's values """
        pass

	# 12.內建方法。判斷鍵是否在字典中，在返回True，不在返回False
    def __contains__(self, *args, **kwargs): # real signature unknown
        pass
		
	# 13.刪除字典中對應k鍵的值
    def __delitem__(self, *args, **kwargs): # real signature unknown
        """ Delete self[key]. """
        pass

	# 14.返回存在Value值得字典
    def __eq__(self, *args, **kwargs): # real signature unknown
        """ Return self==value. """
        pass
		
    def __getattribute__(self, *args, **kwargs): # real signature unknown
        """ Return getattr(self, name). """
        pass

    def __getitem__(self, y): # real signature unknown; restored from __doc__
        """ x.__getitem__(y) <==> x[y] """
        pass

    def __ge__(self, *args, **kwargs): # real signature unknown
        """ Return self>=value. """
        pass

    def __gt__(self, *args, **kwargs): # real signature unknown
        """ Return self>value. """
        pass

    def __init__(self, seq=None, **kwargs): # known special case of dict.__init__
        pass

    def __iter__(self, *args, **kwargs): # real signature unknown
        """ Implement iter(self). """
        pass

    def __len__(self, *args, **kwargs): # real signature unknown
        """ Return len(self). """
        pass

    def __le__(self, *args, **kwargs): # real signature unknown
        """ Return self<=value. """
        pass

    def __lt__(self, *args, **kwargs): # real signature unknown
        """ Return self<value. """
        pass

    @staticmethod # known case of __new__
    def __new__(*args, **kwargs): # real signature unknown
        """ Create and return a new object.  See help(type) for accurate signature. """
        pass

    def __ne__(self, *args, **kwargs): # real signature unknown
        """ Return self!=value. """
        pass

    def __repr__(self, *args, **kwargs): # real signature unknown
        """ Return repr(self). """
        pass

    def __setitem__(self, *args, **kwargs): # real signature unknown
        """ Set self[key] to value. """
        pass

    def __sizeof__(self): # real signature unknown; restored from __doc__
        """ D.__sizeof__() -> size of D in memory, in bytes """
        pass

    __hash__ = None
 

# 15.計算字典元素個數，即鍵的總數
def len(*args, **kwargs): # real signature unknown
    """ Return the number of items in a container. """
    pass
	
# 16.判斷字典型別(相當於呼叫了type類中的__init__()初始化方法)
def __init__(cls, what, bases=None, dict=None): # known special case of type.__init__
    """
    type(object_or_name, bases, dict)
    type(object) -> the object's type
    type(name, bases, dict) -> a new type
    # (copied from class doc)
    """
    pass