各种推导式

列表推导式 [结果 for循环 if]
字典推导式 {结果(k:v) for循环 if}
集合推导式 {结果(k) for循环 if}

# 生成列表: python1->python18
# lst = []
# for i in range(1, 19):
#     lst.append("python%s期" % i)
#
# print(lst)
# 列表推导式 [结果 for循环 if条件]


# lst = ["python%s期" % i for i in range(1, 19)]
# print(lst)

# 生成列表.类表中装的数据是 1-100之间所有的偶数的平方

# lst = [i**2 for i in range(1, 101) if i%2 == 0]
# print(lst)

# 筛选出列表中姓张的同学, lst = ["张无忌", "吴奇隆", "张诗诗", "范冰冰", "张翠山"]
# lst = ["张无忌", "吴奇隆", "张诗诗", "范冰冰", "张翠山"]
# lst2 = [name for name in lst if name.startswith("张")]
# print(lst2)

# # 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']]
#
# lst = [name for el in names for name in el if name.count("e") == 2]
# print(lst)


# 字典推导式
# 语法: { 结果(key:value) for循环 if条件}
# lst = [11,22,33]  # {0:11, 1:22, 2:33}
#
# dic = {i:lst[i] for i in range(len(lst))}
# print(dic)

# 练习: {"主食": "炒面", "副食": "小拌菜", "汤":"疙瘩汤"}
# 把字典的key和value互换, 生成新字典
# dic =  {"主食": "炒面", "副食": "小拌菜", "汤":"疙瘩汤"}
# d = { v:k for k, v in dic.items()}
# print(d)

# 集合推导式 {k for循环 if 条件}

# 没有元组推导式

# g = (i for i in range(10)) # 生成器表达式
#
# print(g)  # <generator object <genexpr> at 0x0000000009E573B8>
#
# print(g.__next__()) # 0
# print(g.__next__()) # 1
# print(g.__next__()) # 2
# print(g.__next__()) # 3
# print(g.__next__()) # 4
# print(g.__next__()) # 5
# print(g.__next__()) # 6
# print(g.__next__()) # 7
# print(g.__next__()) # 8
# print(g.__next__()) # 9
# # print(g.__next__()) # ??? StopIteration
#
#
# g = (i for i in range(10)) # 生成器表达式

# 生成器函数
# def func():
#     print(111)
#     yield 222
#
# # 惰性机制, 只能向前
# g = func()  # 创建生成器
# g1 = (i for i in g) # 生成器表达式
# g2 = (i for i in g1) # 生成器表达式
#
# #
# print(list(g1))
# print(list(g)) # for -> __next__()
# print(list(g2))