python3_scrapy包Field类方法及属性剖析、字典（dict）类方法及属性剖析_scrapy.field

1.Field类简介

①Field对象指明了每个字段的元数据（任何元数据），Field对象接受的值没有任何限制

②设置Field对象的主要目就是在一个地方定义好所有的元数据

③注意，声明item的Field对象，并没有被赋值成class属性。（可通过item.fields进行访问）

④Field类仅是内置字典类（dict）的一个别名，并没有提供额外的方法和属性。被用来基于类属性的方法来支持item生命语法。

【Field类源码】

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

2.dict类源码剖析

类内部方法

class dict(object):
    """
    dict() -> 创建空字典
    dict(mapping)  -> 从映射对象的键值对中初始化新字典{"key":value}
    dict(iterable) -> 从迭代器初始化字典 d[key] = value
    dict(**kwargs) -> 使用字典初始化新字典
    """
	
	# 1.清除字典内部所有内容 -> 空字典
    def clear(self):
        pass
 
	# 2.字典dict的复制
    def copy(self):
        """ dict_copy = D.copy()"""
        pass
 
	# 3.静态方法。返回一个新的字典，其中包含来自迭代器的键，以及对应的值
    @staticmethod # known case
    def fromkeys(*args, **kwargs): # real signature unknown
        pass
 
	# 4.返回指定键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历的(键，值)对
    def items(self): # real signature unknown; restored from __doc__
        pass
 
	# 6.以列表形式返回一个字典所有的键
    def keys(self): # real signature unknown; restored from __doc__
        pass
		
	# 7.删除字典给定键k所对应的值，返回值为被删除的值。k值必须给出。否则，返回d值。
    def pop(self, k, d=None): # real signature unknown; restored from __doc__
        pass
 
	# 8.随机返回并删除字典中的一对键和值
    def popitem(self): # real signature unknown; restored from __doc__
        pass
 
		
	# 9.和get()类似, 但如果键k不存在于字典中，将会添加键并将值设为d
    def setdefault(self, k, d=None): # real signature unknown; restored from __doc__
        pass
 
	# 10.将字典2中的键值对更新入调用字典中
    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.内置方法。判断键是否在字典中，在返回True，不在返回False
    def __contains__(self, *args, **kwargs): # real signature unknown
        pass
		
	# 13.删除字典中对应k键的值
    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.计算字典元素个数，即键的总数
def len(*args, **kwargs): # real signature unknown
    """ Return the number of items in a container. """
    pass
	
# 16.判断字典类型(相当于调用了type类中的__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