Python 3.6 生成器

# 列表生成式

a = [x for x in range(10)]
print(a)
# [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

b = [x * 2 for x in range(10)]
print(b)
# [0, 2, 4, 6, 8, 10, 12, 14, 16, 18]

c = [x * 2 for x in a]
print(c)
# [0, 2, 4, 6, 8, 10, 12, 14, 16, 18]

d = [x * x for x in a]
print(d)


# [0, 1, 4, 9, 16, 25, 36, 49, 64, 81]

def f(x):
    return x * x


e = [f(x) for x in a]
print(e)
# [0, 1, 4, 9, 16, 25, 36, 49, 64, 81]

# 快速獲取容器內的值
li = [1, "2", "3"]
a, b, c = li
print(type(a))
# <class 'int'>
print(a)
# 1
print(type(b))
# <class 'str'>
print(b)
# 2
print(type(c))
# <class 'str'>
print(c)
# 3
print("---------------------------------------------------")
# 生成器 Part2

s = (x for x in range(10))

print(next(s))  # 0
print(next(s))  # 1
print(next(s))  # 2
print(next(s))  # 3

for i in s:
    print(i)

    # 5
    # 6
    # 7
    # 8
    # 9
    # s是一個生成器，他不會先在內存裏生成所需要的值，每一次next他會生成一個值，然後取出
    # 當next的時候，他會有一個位置標記，記錄當前讀到哪裏了，超過範圍就會報錯，for語句會自動讀到最後一個

# 同一個對象，都會被標記位置，但是可以獲取另外一個對象，位置是一個對象的屬性，每個對象都會有自己的位置
s = (x for x in range(10))

print(next(s))  # 0
print(next(s))  # 1
print(next(s))  # 2
print(next(s))  # 3
print("---------------------------------------------------")


# 生成器 Part3 yield
# 這種寫法也可以創建生成器，func1會返回一個生成器對象
# yield代表每一次next執行的位置，yield後面跟着的參數，是當運行到這一行yield的時候返回值，具體看代碼就能明白了
def func1():
    print("OK")
    yield 10
    print("NO")
    yield "aaa"


f = func1()
next(f)
# OK
next(f)
# NO

f2 = func1()
print(next(f2))
# OK
# 10

print(next(f2))
# NO
# aaa

for i in func1():
    print(i)
    print("^^^^^")

    # OK
    # 10
    # ^^^^^
    # NO
    # aaa
    # ^^^^^

for i in func1():
    print(i)
    print("^^^^^")

    # OK
    # 10
    # ^^^^^
    # NO
    # aaa
    # ^^^^^