Python:collections.nametuple ()--mapping names to sequence elements

Questions: access the list or elements in a tuple by subscript

Answer: Collections.namedtuple () solves this problem by using a tuple object

This function is actually a factory method that returns a subclass of the standard tuple type in Python, needs to pass a type name and field to it, and then it returns a class that initializes a class that passes values for the defined fields.

EG1:

1.

>>> from collections Import Namedtuple
>>> subscriber = namedtuple (' subscriber ', [' addr ', ' joined '])
>>> Sub = subscriber (' [email protected] ', ' 2012-10-19 ')
>>> Sub
Subscriber (addr= ' [email protected] ', joined= ' 2012-10-19 ')
>>> sub.addr
' [Email protected] '
>>> sub.joined
' 2012-10-19 '

2. Support Index and decompression

>>> addr, joined = Sub
>>> Addr
' [Email protected] '
>>> joined
' 2012-10-19 '

EG2:

1. One use of named tuples freed from subscript operation

>>>from Collections Import Namedtuple
>>>stock = namedtuple (' Stock ', [' name ', ' shares ', ' price '])
>>>def Compute_cost (Records):
... Total = 0.0
... for rec in records:
... s = Stock (*rec)
... Total + = S.shares * S.Price
.. return Total

2. Another use of named tuples is as a substitute for dictionaries.

Dictionary storage requires more memory space, and if you need to build a very large data structure that contains a dictionary, it is more efficient to use tuples, and it is important to note that named tuples cannot be changed

>>> s = Stock (' ACME ', 100, 123.45)
>>> s
Stock (name= ' ACME ', shares=100, price=123.45)
>>> S.shares = 75
Traceback (most recent):
File "<stdin>", line 1, in <module>
Attributeerror:can ' t set attribute

If you really need to change the properties of a named tuple, you can use the _replace () method of the named tuple instance, which creates a completely new named tuple and replaces the corresponding field with the new value

>>> s = s._replace (shares=75)
>>> s
Stock (name= ' ACME ', shares=75, price=123.45)

It is a very convenient way to populate the data. You can create a prototype tuple that contains default values , and then use the Replace () method to create a new instance of the value that has been updated. For example:
>>>from Collections Import Namedtuple
>>>stock = namedtuple (' Stock ', [' name ', ' shares ', ' price ', ' Date ', ' time ')
Stock_prototype = Stock ("', 0, 0.0, none, none)
>>>def Dict_to_stock (s):
... return stock_prototype._replace (**s)

Here's how it's used:
>>> a = {' name ': ' ACME ', ' shares ': +, ' price ': 123.45}
>>> Dict_to_stock (a)
Stock (name= ' ACME ', shares=100, price=123.45, Date=none, Time=none)
>>> B = {' name ': ' ACME ', ' shares ': +, ' price ': 123.45, ' date ': ' 12/17/2012 '}
>>> Dict_to_stock (b)
Stock (name= ' ACME ', shares=100, price=123.45, date= ' 12/17/2012 ', Time=none)

If the goal is to define an efficient data structure that needs to update many instance properties, named tuples are not the best choice, consider defining a class for a __slots__ method

Python:collections.nametuple ()--mapping names to sequence elements