源码解释:
def namedtuple(typename, field_names, *, rename=False, defaults=None, module=None): """Returns a new subclass of tuple with named fields. >>> Point = namedtuple('Point', ['x', 'y']) >>> Point.__doc__ # docstring for the new class 'Point(x, y)' >>> p = Point(11, y=22) # instantiate with positional args or keywords >>> p[0] + p[1] # indexable like a plain tuple 33 >>> x, y = p # unpack like a regular tuple >>> x, y (11, 22) >>> p.x + p.y # fields also accessible by name 33 >>> d = p._asdict() # convert to a dictionary >>> d['x'] 11 >>> Point(**d) # convert from a dictionary Point(x=11, y=22) >>> p._replace(x=100) # _replace() is like str.replace() but targets named fields Point(x=100, y=22) """
语法结构:
namedtuple(typename, field_names, *, rename=False, defaults=None, module=None)
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typename: 代表新建的一个元组的名字。
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field_names: 是元组的内容,是一个类似list的[‘x’,‘y’]
命名元组,使得元组可像列表一样使用key访问(同时可以使用索引访问)。
collections.namedtuple 是一个工厂函数,它可以用来构建一个带字段名的元组和一个有名字的类.
创建一个具名元组需要两个参数,一个是类名,另一个是类的各个字段的名字。
存放在对应字段里的数据要以一串参数的形式传入到构造函数中(注意,元组的构造函数却只接受单一的可迭代对象)。
命名元组还有一些自己专有的属性。最有用的:类属性_fields、类方法 _make(iterable)和实例方法_asdict()。
示例代码1:
from collections import namedtuple # 定义一个命名元祖city,City类,有name/country/population/coordinates四个字段city = namedtuple('City', 'name country population coordinates')tokyo = city('Tokyo', 'JP', 36.933, (35.689, 139.69))print(tokyo) # _fields 类属性,返回一个包含这个类所有字段名称的元组print(city._fields) # 定义一个命名元祖latLong,LatLong类,有lat/long两个字段latLong = namedtuple('LatLong', 'lat long')delhi_data = ('Delhi NCR', 'IN', 21.935, latLong(28.618, 77.208)) # 用 _make() 通过接受一个可迭代对象来生成这个类的一个实例,作用跟City(*delhi_data)相同delhi = city._make(delhi_data) # _asdict() 把具名元组以 collections.OrderedDict 的形式返回,可以利用它来把元组里的信息友好地呈现出来。print(delhi._asdict())
运行结果:
示例代码2:
from collections import namedtuple Person = namedtuple('Person', ['age', 'height', 'name'])data2 = [Person(10, 1.4, 'xiaoming'), Person(12, 1.5, 'xiaohong')]print(data2) res = data2[0].ageprint(res) res2 = data2[1].nameprint(res2)
运行结果:
示例代码3:
from collections import namedtuplecard = namedtuple('Card', ['rank', 'suit']) # 定义一个命名元祖card,Card类,有rank和suit两个字段class FrenchDeck(object): ranks = [str(n) for n in range(2, 5)] + list('XYZ') suits = 'AA BB CC DD'.split() # 生成一个列表,用空格将字符串分隔成列表 def __init__(self): # 生成一个命名元组组成的列表,将suits、ranks两个列表的元素分别作为命名元组rank、suit的值。 self._cards = [card(rank, suit) for suit in self.suits for rank in self.ranks] print(self._cards) # 获取列表的长度 def __len__(self): return len(self._cards) # 根据索引取值 def __getitem__(self, item): return self._cards[item]f = FrenchDeck()print(f.__len__())print(f.__getitem__(3))
运行结果:
示例代码4:
from collections import namedtuple person = namedtuple('Person', ['first_name', 'last_name']) p1 = person('san', 'zhang')print(p1)print('first item is:', (p1.first_name, p1[0]))print('second item is', (p1.last_name, p1[1]))
运行结果:
示例代码5: 【_make 从存在的序列或迭代创建实例】
from collections import namedtuplecourse = namedtuple('Course', ['course_name', 'classroom', 'teacher', 'course_data'])math = course('math', 'ERB001', 'Xiaoming', '09-Feb')print(math)print(math.course_name, math.course_data)course_list = [ ('computer_science', 'CS001', 'Jack_ma', 'Monday'), ('EE', 'EE001', 'Dr.han', 'Friday'), ('Pyhsics', 'EE001', 'Prof.Chen', 'None')]for k in course_list: course_i = course._make(k) print(course_i)
运行结果:
示例代码6: 【_asdict 返回一个新的ordereddict,将字段名称映射到对应的值】
from collections import namedtupleperson = namedtuple('Person', ['first_name', 'last_name'])zhang_san = ('Zhang', 'San')p = person._make(zhang_san)print(p)# 返回的类型不是dict,而是orderedDictprint(p._asdict())
运行结果:
示例代码7: 【_replace 返回一个新的实例,并将指定域替换为新的值】
from collections import namedtupleperson = namedtuple('Person', ['first_name', 'last_name'])zhang_san = ('Zhang', 'San')p = person._make(zhang_san)print(p)p_replace = p._replace(first_name='Wang')print(p_replace)print(p)p_replace2 = p_replace._replace(first_name='Dong')print(p_replace2)
运行结果:
示例代码8: 【_fields 返回字段名】
from collections import namedtupleperson = namedtuple('Person', ['first_name', 'last_name'])zhang_san = ('Zhang', 'San')p = person._make(zhang_san)print(p)print(p._fields)
运行结果:
示例代码9: 【利用fields可以将两个namedtuple组合在一起】
from collections import namedtupleperson = namedtuple('Person', ['first_name', 'last_name'])print(person._fields)degree = namedtuple('Degree', 'major degree_class')print(degree._fields)person_with_degree = namedtuple('person_with_degree', person._fields + degree._fields)print(person_with_degree._fields)zhang_san = person_with_degree('san', 'zhang', 'cs', 'master')print(zhang_san)
运行结果:
示例代码10: 【field_defaults】
from collections import namedtupleperson = namedtuple('Person', ['first_name', 'last_name'], defaults=['san'])print(person._fields)print(person._field_defaults)print(person('zhang'))print(person('Li', 'si'))
运行结果:
示例代码11: 【namedtuple是一个类,所以可以通过子类更改功能】
from collections import namedtuplePoint = namedtuple('Point', ['x', 'y'])p = Point(4, 5)print(p)class Point(namedtuple('Point', ['x', 'y'])): __slots__ = () @property def hypot(self): return self.x + self.y def hypot2(self): return self.x + self.y def __str__(self): return 'result is %.3f' % (self.x + self.y)aa = Point(4, 5)print(aa)print(aa.hypot)print(aa.hypot2)
运行结果:
示例代码12: 【注意观察两种写法的不同】
from collections import namedtuple Point = namedtuple("Point", ["x", "y"])p = Point(11, 22)print(p)print(p.x, p.y) # namedtuple本质上等于下面写法class Point2(object): def __init__(self, x, y): self.x = x self.y = yo = Point2(33, 44)print(o)print(o.x, o.y)
运行结果:
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