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Source code explanation:
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) """
Grammar structure:
namedtuple(typename, field_names, *, rename=False, defaults=None, module=None)
named tuple, making the tuple It can be accessed using key like a list (and can also be accessed using index).
collections.namedtuple is a factory function that can be used to construct a tuple with field names and a named class.
Creating a named tuple requires two parameters, one is the class name, and the other is the name of each field of the class.
The data stored in the corresponding field must be passed into the constructor in the form of a series of parameters (note that the tuple constructor only accepts a single iterable object).
Named tuples also have some unique properties of their own. The most useful: class attributes _fields, class method _make(iterable) and instance method _asdict().
Sample code 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())
Running result:
Sample code 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].age print(res) res2 = data2[1].name print(res2)
Running result:
##Sample code 3:
from collections import namedtuple card = 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))
Run result:
Example code 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]))
Run Result:
Sample code 5: [_make creates an instance from an existing sequence or iteration]
from collections import namedtuple course = 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)
Run result:
Sample code 6: [_asdict returns a new ordereddict, mapping field names to corresponding values]
from collections import namedtuple person = 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orderedDict print(p._asdict())
Run result:
Sample code 7: [_replace returns a new instance and replaces it with Replace the specified field with the new value】
from collections import namedtuple person = 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)
Running result:
##Sample code 8: 【 _fields returns field name]from collections import namedtuple
person = namedtuple('Person', ['first_name', 'last_name'])
zhang_san = ('Zhang', 'San')
p = person._make(zhang_san)
print(p)
print(p._fields)
Sample code 9:
[Using fields can Combine two namedtuples]from collections import namedtuple
person = 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)
Sample code 10:
【 field_defaults】from collections import namedtuple
person = namedtuple('Person', ['first_name', 'last_name'], defaults=['san'])
print(person._fields)
print(person._field_defaults)
print(person('zhang'))
print(person('Li', 'si'))
Sample code 11:
[namedtuple is a class, so Functions can be changed through subclasses]from collections import namedtuple
Point = 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)
##Sample code 12:
[Note Observe the difference between the two writing methods]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 = y o = Point2(33, 44) print(o) print(o.x, o.y)Running results:
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