如何将“命名元组”更改为 Python 中的类？

Question

Can anyone give an example?

What's the difference between using variables in classes and in namedtuples?

Answer 1

The return value of namedtuple is a class. No dark magic. You do not need to "convert" a namedtuple return into a class; it returned exactly that.

namedtuple creates a new class that inherits from __builtin__.tuple . When you call namedtuple('Point', 'x y')(1, 0) , you're getting is the tuple object (1, 0) with the following syntactic sugar:

• a __dict__ mapping where {'x': 1, 'y', 0}
• two properties x and y that call __getitem__(0) and __getitem__(1) respectively.
• a __repr__ method that returns 'Point(x=1, y=0)'

Other than this, it's just a tuple object. Its attributes and number of attributes are immutable.

However, I suspect you mean you want to take nametuple('Point', 'x, y') and instead get:

class Point:
    def __init__(x, y):
        self.x = x
        self.y = y

In this case you are misusing nametuple , and should instead be using type :

def init(self, x, y):
    self.x, self.y = x, y
Point = type('Point', (object,), {'__init__': init})

Answer 2

Very vague question.

I suppose that you mean constructions like

myPoint1 = namedtuple('myPoint1','x y')

and

class myPoint2(object):
    __slots__ = ['x','y']
    def __init__(self, x, y)
        self.x = x
        self.y = y

myPoint1 is faster in access by index my_point1[0] , my_point1[1] (where 0 stands for x , and 1 stands for y ). But it's slower in access by attr my_point1.x , my_point1.y because of double lookups and additional function executing (see source - it's well documentated about how does namedtuple work)

myPoint2 is only accessable by attr my_point2.x , my_point2.y . And accessing by attr myPoint2 is faster than accessing by attr myPoint1 .

Also if you dont use __slots__ , every instance would consume more memory because dict of attrs/methods is created for every instance (for dynamically tune them - add or remove attrs, fields, methods, etc), whether slots is created once for class only.

Shortly, namedtuple returns tuple subclass that commonly works as tuple , but which data is also accessable by specified attrs.

Answer 3

I think OP wants to be explit about the class definition for a data structure which is currently a namedtuple. namedtuple([...], verbose=True) is likely what you're looking for:

>>> from collections import namedtuple
>>> Pooper = namedtuple('Pooper', ('poop_length','poop_width'))
>>> Pooper(7.5, 1.5)
Pooper(poop_length=7.5, poop_width=1.5)
>>> Pooper = namedtuple('Pooper', ('poop_length','poop_width'), verbose=True)
class Pooper(tuple):
    'Pooper(poop_length, poop_width)'
    __slots__ = ()
    _fields = ('poop_length', 'poop_width')

    def __new__(_cls, poop_length, poop_width):
        'Create new instance of Pooper(poop_length, poop_width)'
        return _tuple.__new__(_cls, (poop_length, poop_width))

    @classmethod
    def _make(cls, iterable, new=tuple.__new__, len=len):
        'Make a new Pooper object from a sequence or iterable'
        result = new(cls, iterable)
        if len(result) != 2:
            raise TypeError('Expected 2 arguments, got %d' % len(result))
        return result

    def __repr__(self):
        'Return a nicely formatted representation string'
        return 'Pooper(poop_length=%r, poop_width=%r)' % 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 Pooper object replacing specified fields with new values'
        result = _self._make(map(kwds.pop, ('poop_length', 'poop_width'), _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

    poop_length = _property(_itemgetter(0), doc='Alias for field number 0')

    poop_width = _property(_itemgetter(1), doc='Alias for field number 1')

Answer 4

from collections import namedtuple as nt

human_nt = nt('Human_nt', 'name, age')
peter_nt = human_nt('Peter', 20)

class Human_cls (human_nt):
     def some_methods(self):
          pass

peter_cls = Human_cls(**peter_nt._asdict())