天天最新:python中namedtuple函数的用法解析
来源:脚本之家    时间:2022-08-31 15:48:04

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:


(资料图)

namedtuple(typename, field_names, *, rename=False, defaults=None, module=None)
typename: 代表新建的一个元组的名字。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].age
print(res)
 
res2 = data2[1].name
print(res2)

运行结果:

示例代码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))

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 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)

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 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())

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 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)

运行结果:

示例代码8:【_fields 返回字段名】

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)

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 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)

运行结果:

示例代码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"))

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 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)

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 = y
o = Point2(33, 44)
print(o)
print(o.x, o.y)

运行结果:

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