python learning journey

In this chapter, the author briefly introduces the python data model, mainly some special methods of python. For example, __len__, __getitem__. And use a playing card program to explain these methods

First introduce the difference between Tuple and nametuple:

Nametuple is similar to a tuple type of data. In addition to being able to access data using indexes, it also supports accessing data using convenient property names.

Traditional tuple access is as follows. Access to each element must be found via index. This method of finding is very unintuitive

tup1=(,,)
tup1[1]

Use nametuple to construct:

tup2=namedtuple(,[,,])
t1=tup2(,,)
t1
t1.age
t1.height
t1.name

得到结果如下，namedtupel中tuple2是类型名，name,age,height是属性名字

从上面的访问可以看到，直接用t1.age的方法访问更加直观。当然也可以用索引比如t1[0]的方法来访问

namedtupe1 also supports iterative access:

t t1:
    t

和元组一样，namedtupel中的元素也是不可变更的。如果执行t1.age+=1。将会提示无法设置元素

Traceback (most recent call last):

File "E:/py_prj/fluent_py.py", line 17, in

t1.age+=1

AttributeError: can't set attribute

Let’s take a look at the playing card example in the book. The code is as follows:

collections namedtuple

Card=namedtuple(,[,])

FrenchDeck:
    ranks=[str(n) n range(2,11)] + list()
    suits=.split()
    __init__(self):
        self._cards=[Card(rank,suit) suit self.suits

rrree

First, the card tuple Card is defined, rank represents the card number, and suit represents the card suit. Then FrenchDeck first defines the specific meaning of ranks and suit. Initialize self._cards in __init__.

__len__Feedback the length of self._cards. __getitem__ returns the specific card value.

The result is as follows, the length of the card is 52, where deck[1] is Card(rank='3',suit='spades')

You can see that len(deck) actually calls the __len__ method. deck[1] calls __getitem__

Due to the __getitem__ method, iterative access can also be performed, as follows:

rank self.ranks]
    __len__(self):
        len(self._cards)
    __getitem__(self, position):
        self._cards[position]

__name__==:
    deck=FrenchDeck()
    len(deck)
    deck[1]

Since it is iterable, Then we can simulate the mechanism of random card dealing.

d deck:
    d

from random import choice

Get the result:

Card(rank='9', suit='hearts')

Let's look at another example, about Vector operations. For example, there is vector 1 vector1(1,2) and vector 2 vector2(3,4). Then the result of vector1+vector2 should be (4,6). Vector1 and vector2 are both vectors, how to implement the operation? The method is __add__,__mul__

The code is as follows:

print choice(deck)

vector:
    __init__(self,x=0,y=0):
        self.x=x
        self.y=y
    __repr__(self):
        % (self.x,self.y)
    __abs__(self):
        hypot(self.x,self.y)
    __bool__(self):
        bool(abs(self))
    __add__(self,other):
        x=self.x+other.x
        y=self.y+other.y
        vector(x,y)
    __mul__(self, scalar):
        vector(self.x*scalar,self.y*scalar)

The operation result is as follows:

##Here__add__,__mul__,__abs__ The operations of vector addition, multiplication, and modulus are implemented respectively.

It is worth mentioning the __repr__ method. This method is called when the object needs to be printed. For example, when printing vector(1,2), vector(1,2) is obtained. Otherwise, it is a string representing the object: . The functions of __repr__ and __str__ are similar

__name__==:
    v1=vector(1,2)
    v2=vector(2,3)
    v1+v2
    abs(v1)
    v1*3

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