python-生成器

# 生成器函数，函数里只要有yield 关键字

def gen_func():
    yield 1
    yield 2
    yield 3


# 斐波拉契（当位数等于前两位数之和） 0 1 1 2 3 5 8
# 惰性求值 ，掩饰求值提供

# 只返回当位的值
def fib(index):
    if index <= 2:
        return 1
    else:
        return fib(index-1) +fib(index-2)

print(fib(5))

# 返回当位前面所有的值
def fib1(index):
    re_list = []
    n,a,b = 0,0,1

    while n<index:
        re_list.append(b)
        a,b = b,a+b
        n+=1
    return re_list

print(fib1(50))


# 生成器完成
def gen_fib(index):
    n, a, b = 0, 0, 1
    while n < index:
        yield b
        a, b = b, a + b
        n += 1

for data in gen_fib(10):
    print(data)


if __name__ == '__main__':
    gen = gen_func()
    for value in gen:
        print(value)

 

读大文件案例

def myreadlines(f,newline):
    # 定义一个缓存空间
    buf = ''
    while True:
        while newline in buf:
            pos = buf.index(newline)
            yield buf[:pos]
            buf = buf[pos+len(newline):]
        chunk = f.read(4096)
        
        if not chunk:
            # 说明已经读到了文件结尾
            yield buf
            break
        buf+=chunk
        
with open("input.txt") as f:
    for line in myreadlines(f,"{|}"):
        print(line)