Question

是否有可以重复最近迭代的break和continue等命令？

例如，抛出异常时。

for i in range(0,500):
    try:
        conn = getConnection(url+str(i))
        doSomething(conn)
    except:
        repeat

让我们进行迭代，其中i变量的值为6。在此迭代期间，发生了一些连接错误。我想重复这个迭代。

是否有可以做到这一点的命令？

当然我可以这样做：

i=0
while i!=500:
    try:
        conn = getConnection(url+str(i))
        doSomething(conn)
        i+=1
    except:
        pass

Answer 1

不，没有命令＆＃34;倒带＆＃34; Python中的for循环。

您可以在for循环中使用while True:循环：

for i in range(500):
    while True:
        try:
            conn = getConnection(url+str(i))
            doSomething(conn)
        except Exception: # Replace Exception with something more specific.
            continue
        else:
            break

或没有else:：

for i in range(500):
    while True:
        try:
            conn = getConnection(url+str(i))
            doSomething(conn)
            break
        except Exception: # Replace Exception with something more specific.
            continue

但我个人认为您提出的解决方案更好，因为它避免了缩进级别。

Answer 2

for i in range(500):
    while True
        try:
            conn = getConnection(url+str(i))
            break
        except Exception: # still allows to quit with KeyboardInterrupt
            continue
    do_your_stuff()

这看起来有点风险，但是，您至少应该在while块中启用一些日志记录。

如果您希望在更多地方使用它，您可以编写一个简单的装饰器：

def keep_trying(fn, *args, **kwargs):
    def inner(*args, **kwargs):
        while True:
            try:
                return fn(*args, **kwargs)
            except Exception:
                continue
    return inner

# later you can use it simple like this:
for i in range(500):
    conn = keep_trying(getConnection)(url+str(i))

Answer 3

您可以使用生成器：

def process_connections(n_connections, url, max_tries=50):
    i = 0
    try_count = 0
    while i < n_connections:
        try:
            conn = getConnection(url+str(i))
            yield conn
        except:
            try_count += 1
            if try_count > max_tries:
                raise Exception("Unable to connect after %s tries" % max_tries)
        else:
            i += 1 # increments only if no exception

您执行操作：

for conn in process_connections(500, url):
    do_something(conn)

Answer 4

为什么不使用if声明？

n=6
i=0
while i!=500:
    failed = False;
    try:
        conn = getConnection(url+str(i))
        doSomething(conn)
        i+=1
    except:
        #handle error
        failed = True;

    #try again if n-th case failed first time
    if(i == n and failed):
        try:
            conn = getConnection(url+str(i))
            doSomething(conn)
        except:
            #handle error

Answer 5

您可以使用嵌套for循环来设置重试操作次数的上限。这是@ PierreAlex的生成器答案但不具备额外功能定义的sam。

for i in range(500):
    for retry in range(10):
        try:
            conn = getConnection(url+str(i))
            doSomething(conn)
        except Exception: # Replace Exception with something more specific.
            time.sleep(1)
    else:
        print "iteration", i, "failed"

如果发生错误，请在循环中重复迭代

5 个答案: