python namedtuple函数的使用

目录先看演示像类一样的访问属性类似字典的访问为什么可以这样？源码解析为什么有类的影子？为什么有字典的影子？先看演示像类一样的访问属性

from collections import namedtupleFriend = namedtuple(’Friend’, [’name’, ’gender’, ’address’, ’star’, ’signature’])RidingRoad = Friend(’RidingRoad’, ’male’, ’Mars’, ’The five-star high praise’, ’Change the world by Program!n’ ’Do what you like!n’ ’Live what you want!’)print(RidingRoad.name)print(RidingRoad.gender)print(RidingRoad.address)print(RidingRoad.star)print(RidingRoad.signature)

RidingRoadmaleMarsThe five-star high praiseChange the world by Program!Do what you like!Live what you want!类似字典的访问

像字典一样访问items、keys、values

for key, value in RidingRoad.__dict__.items(): print(key, value)print('*' * 30)for key in RidingRoad.__dict__.keys(): print(’{}: ’.format(key), eval(’RidingRoad.{}’.format(key)))print('*' * 30)for value in RidingRoad.__dict__.values(): print(value)

(’name’, ’RidingRoad’)(’gender’, ’male’)(’address’, ’Mars’)(’star’, ’The five-star high praise’)(’signature’, ’Change the world by Program!nDo what you like!nLive what you want!’)******************************(’name: ’, ’RidingRoad’)(’gender: ’, ’male’)(’address: ’, ’Mars’)(’star: ’, ’The five-star high praise’)(’signature: ’, ’Change the world by Program!nDo what you like!nLive what you want!’)******************************RidingRoadmaleMarsThe five-star high praiseChange the world by Program!Do what you like!Live what you want!为什么可以这样？

到这里，你应该会有两个疑问：

为什么有类的影子？ 为什么有字典的影子？ 源码解析为什么有类的影子？

看源码的_class_template部分，其实函数内部为我们创了一个类了

# Fill-in the class template class_definition = _class_template.format(typename = typename,field_names = tuple(field_names),num_fields = len(field_names),arg_list = repr(tuple(field_names)).replace('’', '')[1:-1],repr_fmt = ’, ’.join(_repr_template.format(name=name) for name in field_names),field_defs = ’n’.join(_field_template.format(index=index, name=name) for index, name in enumerate(field_names)) ) if verbose:print class_definition

然后_class_template干了什么？对类进行定义

_class_template = ’’’class {typename}(tuple): ’{typename}({arg_list})’ __slots__ = () _fields = {field_names!r} def __new__(_cls, {arg_list}):’Create new instance of {typename}({arg_list})’return _tuple.__new__(_cls, ({arg_list})) @classmethod def _make(cls, iterable, new=tuple.__new__, len=len):’Make a new {typename} object from a sequence or iterable’result = new(cls, iterable)if len(result) != {num_fields:d}: raise TypeError(’Expected {num_fields:d} arguments, got %d’ % len(result))return result def __repr__(self):’Return a nicely formatted representation string’return ’{typename}({repr_fmt})’ % self def _asdict(self):’Return a new OrderedDict which maps field names to their values’return OrderedDict(zip(self._fields, self)) def _replace(_self, **kwds):’Return a new {typename} object replacing specified fields with new values’result = _self._make(map(kwds.pop, {field_names!r}, _self))if kwds: raise ValueError(’Got unexpected field names: %r’ % kwds.keys())return result def __getnewargs__(self):’Return self as a plain tuple. Used by copy and pickle.’return tuple(self) __dict__ = _property(_asdict) def __getstate__(self):’Exclude the OrderedDict from pickling’pass{field_defs}’’’为什么有字典的影子？

看源码的 _asdict部分，这里封装成了有序字典，所以我们可以通过__dict__访问字典的特性了

__dict__ = _property(_asdict) def _asdict(self):’Return a new OrderedDict which maps field names to their values’return OrderedDict(zip(self._fields, self))

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