Python中如何使用生成器？yield关键字详解

# 示例：一个简单的计数器生成器
def count_up_to(n):
    i = 1
    while i <= n:
        print(f"正在生成值: {i}")
        yield i
        i += 1

# 使用生成器
my_counter = count_up_to(3)

print("第一次获取值:")
print(next(my_counter))

print("第二次获取值:")
print(next(my_counter))

print("使用for循环继续获取:")
for num in my_counter:
    print(num)

# 尝试获取更多值，会抛出StopIteration
# print(next(my_counter))

# 读取大文件示例
def read_large_file(file_path):
    with open(file_path, 'r', encoding='utf-8') as f:
        for line in f:
            yield line.strip() # 逐行返回，不一次性加载所有行

# 使用
# for data_line in read_large_file('my_huge_data.log'):
#     process(data_line)

def sub_generator_a():
    yield "Data from A1"
    yield "Data from A2"

def sub_generator_b():
    yield "Data from B1"
    yield "Data from B2"

def main_generator_old_way():
    for item in sub_generator_a():
        yield item
    for item in sub_generator_b():
        yield item

# for data in main_generator_old_way():
#     print(data)

def sub_generator_a():
    yield "Data from A1"
    yield "Data from A2"

def sub_generator_b():
    yield "Data from B1"
    yield "Data from B2"

def main_generator_new_way():
    yield from sub_generator_a()
    yield from sub_generator_b()
    # 甚至可以yield from一个列表或元组
    yield from ["More", "Data"]

# for data in main_generator_new_way():
#     print(data)

def risky_generator():
    yield 1
    # 模拟一个错误
    raise ValueError("Something went wrong inside the generator!")
    yield 2

# 尝试捕获生成器内部抛出的异常
try:
    gen = risky_generator()
    print(next(gen))
    print(next(gen)) # 这里会抛出异常
except ValueError as e:
    print(f"捕获到生成器内部的错误: {e}")

def controlled_generator():
    print("生成器开始")
    try:
        value = yield 1
        print(f"收到外部发送的值: {value}")
        value = yield 2
        print(f"再次收到外部发送的值: {value}")
    except GeneratorExit:
        print("生成器被强制关闭 (GeneratorExit)")
    except Exception as e:
        print(f"生成器内部捕获到异常: {e}")
    finally:
        print("生成器清理完成")
    print("生成器结束")

gen = controlled_generator()
print(next(gen)) # 打印 "生成器开始", 返回 1

try:
    # 从外部抛入一个TypeError
    gen.throw(TypeError, "这是一个外部注入的类型错误")
except StopIteration: # 注意：如果生成器内部捕获并处理了，外部可能不会收到
    print("生成器已停止")
except TypeError as e:
    print(f"外部捕获到异常: {e}") # 如果生成器内部没有捕获，外部会捕获到

def finite_generator():
    yield 'A'
    yield 'B'
    print("生成器已无更多值")

gen = finite_generator()
print(next(gen))
print(next(gen))

try:
    print(next(gen)) # 尝试获取第三个值，会抛出StopIteration
except StopIteration:
    print("生成器已完成迭代，没有更多值了。")

def resource_generator():
    print("资源正在打开...")
    try:
        yield "数据1"
        yield "数据2"
    finally:
        print("资源正在关闭...") # 确保在生成器关闭时执行

gen = resource_generator()
print(next(gen))
gen.close() # 显式关闭生成器，会触发finally块
# 再次尝试next(gen)会直接抛出StopIteration