Python 推导式

# 生成列表: python1->python18
lst = []
for i in range(1, 19):
    lst.append("python%s" % i)

print(lst)
# 列表推导式 [结果 for循环 if条件]


lst = ["python%s" % 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))