葵潭世铿院,红小豆的作用,程序员考试
1. 通过⽣成器函数2. 通过各种推导式来实现⽣成器3. 通过数据的转换也可以获取⽣成器
def func(): print("111") return 222 ret = func() print(ret)
结果: 111 222
def func(): print("111") yield 222 ret = func() print(ret)
结果: <generator object func at 0x10567ff68>
def func(): print("111") yield 222 gener = func() # 这个时候函数不会执⾏. ⽽是获取到⽣成器 ret = gener.__next__() # 这个时候函数才会执⾏. yield的作⽤和return⼀样. 也是返回数据 print(ret)
结果: 111 222
def func(): print("111") yield 222 print("333") yield 444 gener = func() ret = gener.__next__() print(ret) ret2 = gener.__next__() print(ret2) ret3 = gener.__next__() # 最后⼀个yield执⾏完毕. 再次__next__()程序报错, 也就是说. 和return⽆关了. print(ret3)
结果: 111 traceback (most recent call last): 222 333 file "/users/sylar/pycharmprojects/oldboy/iterator.py", line 55, in <module> 444 ret3 = gener.__next__() # 最后⼀个yield执⾏完毕. 再次__next__()程序报错, 也就是说. 和return⽆关了. stopiteration
def cloth(): lst = [] for i in range(0, 10000): lst.append("⾐服"+str(i)) return lst cl = cloth()
def cloth(): for i in range(0, 10000): yield "⾐服"+str(i) cl = cloth() print(cl.__next__()) print(cl.__next__()) print(cl.__next__()) print(cl.__next__())
def eat(): print("我吃什么啊") a = yield "馒头" print("a=",a) b = yield "⼤饼" print("b=",b) c = yield "⾲菜盒⼦" print("c=",c) yield "game over"
gen = eat() # 获取⽣成器 ret1 = gen.__next__() print(ret1) ret2 = gen.send("胡辣汤") print(ret2) ret3 = gen.send("狗粮") print(ret3) ret4 = gen.send("猫粮") print(ret4)
def func(): print(111) yield 222 print(333) yield 444 print(555) yield 666
gen = func() for i in gen: print(i)
结果: 111 222 333 444 555 666
lst = [] for i in range(1, 15): lst.append(i) print(lst)
lst = [i for i in range(1, 15)] print(lst)
[ 结果 for 变量 in 可迭代对象]
lst = ['python%s' % i for i in range(1,15)] print(lst)
[ 结果 for 变量 in 可迭代对象 if 条件 ]
# 获取1-100内所有的偶数 lst = [i for i in range(1, 100) if i % 2 == 0] print(lst)
gen = (i for i in range(10)) print(gen)
结果: <generator object <genexpr> at 0x106768f10>
gen = ("麻花藤我第%s次爱你" % i for i in range(10)) for i in gen: print(i)
gen = (i for i in range(1,100) if i % 3 == 0) for num in gen: print(num)
# 100以内能被3整除的数的平⽅ gen = (i * i for i in range(100) if i % 3 == 0) for num in gen: print(num)
# 寻找名字中带有两个e的⼈的名字 names = [['tom', 'billy', 'jefferson', 'andrew', 'wesley', 'steven','joe'], ['alice', 'jill', 'ana', 'wendy', 'jennifer', 'sherry', 'eva']]
# 不⽤推导式和表达式 result = [] for first in names: for name in first: if name.count("e") >= 2: result.append(name) print(result)
# 推导式 gen = (name for first in names for name in first if name.count("e") >= 2) for name in gen: print(name)
1. 列表推导式比较耗内存,⼀次性加载,⽣成器表达式⼏乎不占⽤内存,使⽤的时候才分配和使⽤内存。2. 得到的值不⼀样,列表推导式得到的是⼀个列表,⽣成器表达式获取的是⼀个⽣成器。
def func(): print(111) yield 222
g = func() # ⽣成器g g1 = (i for i in g) # ⽣成器g1. 但是g1的数据来源于g g2 = (i for i in g1) # ⽣成器g2. 来源g1
print(list(g)) # 获取g中的数据. 这时func()才会被执⾏. 打印111.获取到222. g完毕. print(list(g1)) # 获取g1中的数据. g1的数据来源是g. 但是g已经取完了. g1 也就没有数据了 print(list(g2)) # 和g1同理
# 把字典中的key和value互换 dic = {'a': 1, 'b': '2'} new_dic = {dic[key]: key for key in dic} print(new_dic)
# 在以下list中. 从lst1中获取的数据和lst2中相对应的位置的数据组成⼀个新字典 lst1 = ['jay', 'jj', 'sylar'] lst2 = ['周杰伦', '林俊杰', '邱彦涛'] dic = {lst1[i]: lst2[i] for i in range(len(lst1))} print(dic)
lst = [1, -1, 8, -8, 12] # 绝对值去重 s = {abs(i) for i in lst} print(s)
(结果 for 变量 in 可迭代对象 if 条件筛选)
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