namedtuple是Python中存儲(chǔ)數(shù)據(jù)類型，比較常見(jiàn)的數(shù)據(jù)類型還有有l(wèi)ist和tuple數(shù)據(jù)類型。相比于list，tuple中的元素不可修改，在映射中可以當(dāng)鍵使用。

namedtuple:

namedtuple類位于collections模塊,有了namedtuple后通過(guò)屬性訪問(wèn)數(shù)據(jù)能夠讓我們的代碼更加的直觀更好維護(hù)。

namedtuple能夠用來(lái)創(chuàng)建類似于元祖的數(shù)據(jù)類型，除了能夠用索引來(lái)訪問(wèn)數(shù)據(jù)，能夠迭代，還能夠方便的通過(guò)屬性名來(lái)訪問(wèn)數(shù)據(jù)。

接下來(lái)通過(guò)本文給大家分享python namedtuple()的使用，一起看看吧！

基本定義

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

(1)返回一個(gè)名為typename的新元組子類

(2)新的子類用于創(chuàng)建類似元組的對(duì)象，這些對(duì)象具有可通過(guò)屬性查找訪問(wèn)的字段以及可索引和可??迭代的字段field_names

typename

(1)typename表示這個(gè)子類的名字，比如C++、python、Java中的類名

field_names

(1)field_names是一個(gè)字符串序列，例如['x'，'y']

(2)field_names可以是單個(gè)字符串，每個(gè)字段名都用空格或逗號(hào)分隔，例如'x y'或'x，y'

others

(1)其它的參數(shù)并不常用，這里不再介紹啦

基本樣例

from collections import namedtuple

# 基本例子

Point = namedtuple('Point',['x','y']) # 類名為Point,屬性有'x'和'y'

p = Point(11, y=22) # 用位置或關(guān)鍵字參數(shù)實(shí)例化，因?yàn)?#39;x'在'y'前，所以x=11,和函數(shù)參數(shù)賦值一樣的

print(p[0]+p[1]) # 我們也可以使用下標(biāo)來(lái)訪問(wèn)

# 33

x, y = p # 也可以像一個(gè)元組那樣解析

print(x,y)

# (11, 22)

print(p.x+p.y) # 也可以通過(guò)屬性名來(lái)訪問(wèn)

# 33

print(p) # 通過(guò)內(nèi)置的__repr__函數(shù)，顯示該對(duì)象的信息

# Point(x=11, y=22)

classmethodsomenamedtuple._make(iterable)

(1)從一個(gè)序列或者可迭代對(duì)象中直接對(duì)field_names中的屬性直接賦值，返回一個(gè)對(duì)象

t = [11, 22] # 列表 list

p = Point._make(t) # 從列表中直接賦值，返回對(duì)象

print(Point(x=11, y=22))

# Point(x=11, y=22)

classmethodsomenamedtuple._asdict()

(1)之前也說(shuō)過(guò)了，說(shuō)它是元組，感覺(jué)更像一個(gè)帶名字的字典

(2)我們也可以直接使用_asdict()將它解析為一個(gè)字典dict

p = Point(x=11, y=22) # 新建一個(gè)對(duì)象

d = p._asdict() # 解析并返回一個(gè)字典對(duì)象

print(d)

# {'x': 11, 'y': 22}

classmethodsomenamedtuple._replace(**kwargs)

(1)這是對(duì)某些屬性的值，進(jìn)行修改的，從replace這個(gè)單詞就可以看出來(lái)

(2)注意該函數(shù)返回的是一個(gè)新的對(duì)象，而不是對(duì)原始對(duì)象進(jìn)行修改

p = Point(x=11, y=22) # x=11,y=22

print(p)

# Point(x=11, y=22)

d = p._replace(x=33) # x=33,y=22 新的對(duì)象

print(p)

# Point(x=11, y=22)

print(d)

# Point(x=33, y=22)

classmethodsomenamedtuple._fields

(1)該方法返回該對(duì)象的所有屬性名，以元組的形式

(2)因?yàn)槭窃M，因此支持加法操作

print(p._fields) # 查看屬性名

# ('x', 'y')

Color = namedtuple('Color', 'red green blue')

Pixel = namedtuple('Pixel', Point._fields + Color._fields) # 新建一個(gè)子類，使用多個(gè)屬性名

q = Pixel(11, 22, 128, 255, 0)

print(q)

classmethodsomenamedtuple._field_defaults

(1)該方法是python3.8新增的函數(shù)，因?yàn)槲业陌姹臼?.6，無(wú)法驗(yàn)證其正確性

(2)下面給出官方的示例

Account = namedtuple('Account', ['type', 'balance'], defaults=[0])

print(Account._field_defaults)

#{'balance': 0}

print(Account('premium'))

#Account(type='premium', balance=0)

getattr()函數(shù)

(1)用來(lái)獲得屬性的值

print(getattr(p, 'x'))

# 11

字典創(chuàng)建namedtuple()

(1)從字典來(lái)構(gòu)建namedtuple的對(duì)象

d = {'x': 11, 'y': 22} # 字典

p = Point(**d) # 雙星號(hào)是重點(diǎn)

print(p)

# Point(x=11, y=22)

CSV OR Sqlite3

(1)同樣可以將從csv文件或者數(shù)據(jù)庫(kù)中讀取的文件存儲(chǔ)到namedtuple中

(2)這里每次存的都是一行的內(nèi)容

EmployeeRecord = namedtuple('EmployeeRecord', 'name, age, title, department, paygrade')

import csv

for emp in map(EmployeeRecord._make, csv.reader(open("employees.csv", "r"))):

# 這里每行返回一個(gè)對(duì)象 注意！

print(emp.name, emp.title)

import sqlite3

conn = sqlite3.connect('/companydata') # 連接數(shù)據(jù)庫(kù)

cursor = conn.cursor()

cursor.execute('SELECT name, age, title, department, paygrade FROM employees')

for emp in map(EmployeeRecord._make, cursor.fetchall()):

# 每行返回一個(gè)對(duì)象 注意！

print(emp.name, emp.title)

類的繼承

(1)接下來(lái)用deepmind的開(kāi)源項(xiàng)目graph_nets中的一段代碼來(lái)介紹

NODES = "nodes"

EDGES = "edges"

RECEIVERS = "receivers"

SENDERS = "senders"

GLOBALS = "globals"

N_NODE = "n_node"

N_EDGE = "n_edge"

GRAPH_DATA_FIELDS = (NODES, EDGES, RECEIVERS, SENDERS, GLOBALS)

GRAPH_NUMBER_FIELDS = (N_NODE, N_EDGE)

class GraphsTuple(

# 定義元組子類名 以及字典形式的鍵名(屬性名)

collections.namedtuple("GraphsTuple",

GRAPH_DATA_FIELDS + GRAPH_NUMBER_FIELDS)):

# 這個(gè)函數(shù)用來(lái)判斷依賴是否滿足，和我們的namedtuple關(guān)系不大

def _validate_none_fields(self):

"""Asserts that the set of `None` fields in the instance is valid."""

if self.n_node is None:

raise ValueError("Field `n_node` cannot be None")

if self.n_edge is None:

raise ValueError("Field `n_edge` cannot be None")

if self.receivers is None and self.senders is not None:

raise ValueError(

"Field `senders` must be None as field `receivers` is None")

if self.senders is None and self.receivers is not None:

raise ValueError(

"Field `receivers` must be None as field `senders` is None")

if self.receivers is None and self.edges is not None:

raise ValueError(

"Field `edges` must be None as field `receivers` and `senders` are "

"None")

# 用來(lái)初始化一些參數(shù) 不是重點(diǎn)

def __init__(self, *args, **kwargs):

del args, kwargs

# The fields of a `namedtuple` are filled in the `__new__` method.

# `__init__` does not accept parameters.

super(GraphsTuple, self).__init__()

self._validate_none_fields()

# 這就用到了_replace()函數(shù),注意只要修改了屬性值

# 那么就返回一個(gè)新的對(duì)象

def replace(self, **kwargs):

output = self._replace(**kwargs) # 返回一個(gè)新的實(shí)例

output._validate_none_fields() # pylint: disable=protected-access 驗(yàn)證返回的新實(shí)例是否滿足要求

return output

# 這是為了針對(duì)tensorflow1版本的函數(shù)

# 返回一個(gè)擁有相同屬性的對(duì)象，但是它的屬性值是輸入的大小和類型

def map(self, field_fn, fields=GRAPH_FEATURE_FIELDS): # 對(duì)每個(gè)鍵應(yīng)用函數(shù)

"""Applies `field_fn` to the fields `fields` of the instance.

`field_fn` is applied exactly once per field in `fields`. The result must

satisfy the `GraphsTuple` requirement w.r.t. `None` fields, i.e. the

`SENDERS` cannot be `None` if the `EDGES` or `RECEIVERS` are not `None`,

etc.

Args:

field_fn: A callable that take a single argument.

fields: (iterable of `str`). An iterable of the fields to apply

`field_fn` to.

Returns:

A copy of the instance, with the fields in `fields` replaced by the result

of applying `field_fn` to them.

"""

return self.replace(**{k: field_fn(getattr(self, k)) for k in fields}) # getattr(self, k) 獲取的是鍵值對(duì)中的值, k表示鍵

到此這篇關(guān)于詳解Python中namedtuple的使用的文章就介紹到這了,更多相關(guān)python namedtuple的使用內(nèi)容請(qǐng)搜索我們以前的文章或繼續(xù)瀏覽下面的相關(guān)文章希望大家以后多多支持我們！

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