pylib_namedtuple

目录

• 简述
• API
• 例子

简述

namedtuple 是对tuple的扩展,支持用名称访问tuple中的元素.
Python文档

API

1. collections.namedtuple(typename, field_names, *, rename=False, defaults=None, module=None)

2. classmethod somenamedtuple._make(iterable)
   Class method that makes a new instance from an existing sequence or iterable.

3. somenamedtuple._asdict()
   Return a new dict which maps field names to their corresponding values:

4. somenamedtuple._replace(**kwargs)
   Return a new instance of the named tuple replacing specified fields with new values:

5. somenamedtuple._fields
   Tuple of strings listing the field names. Useful for introspection and for creating new named tuple types from existing named tuples.

6. somenamedtuple._field_defaults
   Dictionary mapping field names to default values.

例子

from collections import namedtuple

# define the named tuple
Point = namedtuple('Point', 'x,y')
Point2 = namedtuple('Point', 'x y')

# create a namedtuple instance
p1 = Point(1, 2)
p2 = Point2(x=3, y=4)

# reference the fields
p1.x   # using the dot.
p1[1]   # using subscript

# the instances are type Point
type(p1)   # 
type(p2)   # 

# the defined namedtuple are type of 'type'
type(Point)   # 
type(Point2)  # 

# as tuple, namedtuple is immutable too, can not change the fields value
p1.x = 4     # WRONG
# instead we can replace the value using api.
p2 = p2._replace(x=4)   # OK

# ---- create instance with _make
Metric = namedtuple('Metric', 'a,b,c,d,e,f,g')
value = [i for i in range(len(Metric._fields))]

# create instance using either _make or init parameters
m1 = Metric(*value)   # Metric(a=0, b=1, c=2, d=3, e=4, f=5, g=6)
m2 = Metric._make(value)   # Metric(a=0, b=1, c=2, d=3, e=4, f=5, g=6)

# convert to a dictionary
m1._asdict()  # {'a': 0, 'b': 1, 'c': 2, 'd': 3, 'e': 4, 'f': 5, 'g': 6}

# ---- extend the namedtuple
# the namedtuple can be subclassed
class Point(namedtuple('Point', 'x, y')):
    def distance_to_origin(self):
        return (self.x ** 2 + self.y ** 2) ** 0.5

    def __str__(self):
        return f'x: {self.x}, y: {self.y}, distance to origin: {self.distance_to_origin()}'

p = Point(x=3, y=4)
str(p)   # 'x: 3, y: 4, distance to origin: 5.0'

# add more fields
Point3D = namedtuple('Point3D', Point._fields + ('z',))
p3d = Point3D(x=1, y=2, z=3)
p3d  # Point3D(x=1, y=2, z=3)