8.python3 practical advanced programming skills (C)

3.1. How to achieve iterables and iterator object

# 3.1 How to achieve iterables and iterator object 

Import Requests
 from collections.abc Import Iterable, Iterator 

class WeatherIterator (Iterator):
     DEF  __init__ (Self, Cities): 
        self.cities = Cities
         # iterations from a list city, index it +1 
        self.index = 0 

    DEF  __next__ (Self):
         # If all cities are iterations over, throwing an exception 
        IF self.index == len (self.cities):
             the raise StopIteration
         # current iteration city 
        city = Self. cities [self.index]
        # Iteration End current city, index it + 1'd 
        self.index + =. 1 return self.get_weather (City) DEF get_weather (Self, City): 
        URL = ' http://wthrcdn.etouch.cn/weather_mini?city= ' + city 
        r = requests.get (url)
         # get the day's weather information 
        the Data = r.json () [ ' the Data ' ] [ ' Forecast ' ] [0]
         # returns the name of the city, maximum and minimum temperatures return city, the Data [ ' High ' ], Data [ ' Low ' ]
        

    
        


class WeatherIterable(Iterable):
    def __init__(self,cities):
        self.cities = cities

    def __iter__(self):
        return WeatherIterator(self.cities)


def show(w):
    for x in w:
        print(x)

weather = WeatherIterable(['北京','上海','广州','深圳','东莞'])
show(weather)

result

3.2 How to use the generator function implemented iterables

# 3.2 How to use the generator function implemented iterables 

from collections.abc Import the Iterable 

class PrimeNumbers (the Iterable):
     DEF  the __init__ (Self, A, B): 
        self.a = A 
        self.b, = B 

    DEF  the __iter__ (Self):
         for K in Range (self.a, self.b,):
             IF self.is_prime (K):
                 the yield K 

    DEF is_prime (Self, K):
         return False IF K <2 the else All (Map ( the lambda X: X K%, Range (2, K))) 

# printing 1-30 direct prime 
PN PrimeNumbers = (. 1, 30 )
 for n- in PN:
     Print (n-)

3.3. How to reverse iteration and how to implement reverse iteration

Reverse iteration

In [75]: l = [1,2,3,4,5]

In [76]: for x in l:
    ...:     print(x)
    ...:
1
2
3
4
5

In [77]: for x in reversed(l):
    ...:     print(x)
    ...:
5
4
3
2
1

To achieve reverse iterator method must implement __reversed__

# 3.3 How reverse iteration and how reverse iteration. 

Class IntRange:
     DEF  the __init__ (Self, A, B, STEP): 
        self.a = A 
        self.b, = B 
        self.step = STEP 

    DEF  the __iter__ (Self): 
        T = self.a
         the while T <= self.b,:
             the yield T 
            T + = self.step 
    
    DEF  __reversed__ (Self): 
        T = self.b,
         the while T> = self.a:
             the yield t
            t -= self.step

fr = IntRange(1, 10, 2)

for x in fr:
    print(x)

print('=' * 30)

#反向迭代
for y in reversed(fr):
    print(y)