实际编程和面试都会遇到的典型问题。
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如何实现可迭代对象和迭代器对象
#可迭代对象
l = [1,2,3,4]
s = 'abcde'
#迭代器对象
t = iter(l)
import requests
from collections import Iterator,Iterable
#实现一个迭代器对象WeatherIterator,__next__方法每次返回一个城市气温
class WeatherIterator(Iterator):
def __init__(self,cities):
self.cities = cities
self.index = 0
def getWeather(city):
r = requests.get(u'http://wthrcdn.etouch.cn/weather_mini?city=' + city)
data = r.json()['data']['forecast'][0]
return '%s: %s ,%s '%(city,data['low'],data['high'])
def __next__(self):
if self.index == len(self.cities):
raise StopIteration
city = self.cities[self.index]
self.index += 1
return getWeather(city)
#实现一个可迭代对象WeatherIterable,__iter__方法返回一个迭代器对象
class WeatherIterable(Iterable):
def __init__(self,cities):
self.cities = cities
def __iter__(self):
return WeatherIterator(self.cities)
#[u'漠河',u'海南',u'乌鲁木齐',u'上海']
for x in WeatherIterable([u'漠河',u'海南',u'乌鲁木齐',u'上海']):
print(x)
如何使用生成器函数实现可迭代对象
# 给定一个可迭代对象的类,它能迭代出给定范围内的所有素数
class PrimeNumber():
def __init__(self,start,end):
self.start = start
self.end = end
def isPrimeNum(self,k):
if k < 2:
return False
for i in range(2,k):
if k % i == 0:
return False
return True
def __iter__(self):
for k in range(self.start,self.end + 1):
if self.isPrimeNum(k):
yield k
for x in PrimeNumber(1,100):
print(x)
如何进行反向迭代以及如何实现反向迭代
#实现一个连续浮点数发生器FloatRange(start,end,step)
# l = [1,2,3,4,5]
# for x in reversed(l):
# print(x)
class FloatRange():
def __init__(self,start,end,step=0.1):
self.start = start
self.end = end
self.step = step
def __iter__(self):
t = self.start
while t <= self.end:
yield t
t += self.step
def __reversed__(self):
t = self.end
while t >= self.start:
yield t
t -= self.step
for x in reversed(FloatRange(1.0,5.5,0.5)):
print(x)
如何对迭代器做切片操作
#有一个文本文件,我们想获取某范围内的内容 eg:100-300lines
import this
f = open('test','w')
f.write(this.s)
f.close()
from itertools import islice
f = open('test','r')
for x in islice(f,3,5):
print(x)
如何在一个for语句中迭代多个可迭代对象
from random import randint
#每个学生有三门成绩(并行)
chese_grade = [randint(60,100) for _ in range(50)]
english_grade = [randint(60,100) for _ in range(50)]
math_grade = [randint(60,100) for _ in range(50)]
for c,e,m in zip(chese_grade,english_grade,math_grade):
print('总分:%3d 语文:%3d 英语:%3d 数学:%3d'%(c+e+m,c,e,m))
#有四个班,一次英语考试的成绩存储在四个列表里,统计90以上的人数(串行)
from itertools import chain
chain([1,2,3,4],['a','b','c'])
english_grade1 = [randint(60,100) for _ in range(45)]
english_grade2 = [randint(60,100) for _ in range(53)]
english_grade3 = [randint(60,100) for _ in range(49)]
english_grade4 = [randint(60,100) for _ in range(35)]
count = 0
for x in chain(english_grade1,english_grade2,english_grade3,english_grade4):
if x >= 90:
count += 1
print(count)
