如何在 Python 中循环一系列函数

Question

我想让main((重复，直到它不能再重复，因为function_one((上的"找不到文件"。当我执行代码时，它从function_one到function_three并停止在那里。如何循环 main(( 以便它再次重复函数序列？

 def main():
        (f,r) = function_one()
        (x,z) = function_two(f,r)
        function_three(x,z)

Answer 1

使用 while 循环：

def main():
    while True:
        try:
            (f, r) = function_one()
            (x, z) = function_two(f, r)
            function_three(x, z)
        except WhateverErrors:
            break

Answer 2

正如已经建议的那样，带有 try/except 的 while 循环会很好用，但要小心你捕获的内容。尽可能具体。这篇文章中提供了更多信息。

如果您的函数并非都以异常结尾，还可以通过手动引发异常来让它们返回成功或失败。

def main():
    c = float(1.00)
    # Uncomment the following line to see an unplanned exception / bug.
    # c = float(0.00)
    # That's is why it's important to only catch exceptions you are
    # expexting.
    # If you catch everything you won't see your own mistakes.
    while True:
        c += 2
        print('Main loop')
        try:
            (f, r) = function_one(c)
            (x, z) = function_two(f, r)
            function_three(x, z)
        except IOError:
            print('Controlled end, due to an IOError')
            break
        except ValueError as e:
            print('Intentionally stopped: %s' % e)
            break
    print("Program end")

# Will cause IOERROR if "thestar.txt" does not exist,
# Will continue on if you create the file.
def function_one(c):
    print('function_one')
    with open('thestar.txt', 'r') as bf:
        f = bf.read()
    # Doing work on the data ...
    r = 100 - c
    return (f, r)

# If the file does not contain the text "Cleese",
# this will hand-raise an exception to stop the loop.
def function_two(f, r):
    print('function_two')
    if 'cleese' in f.lower():
        x = 100 / r
        z = 'John ' + f
    else:
        raise ValueError('The parrot is just sleeping')
    return (x, z)

# you need to write "Cleese" to thestar.txt to get this far and keep
# the main loop going.
def function_three(x, z):
    print('function_three')
    # This is what decides when we are finished looping
    if x > 1:
        print('%s:%s' % (x, z))
    else:
        # Another diliberately raised exception to break the loop
        raise ValueError('The parrot is dead!')

if __name__ == '__main__':
    main()

使用变量而不是异常来做到这一点是完全可以的，但这种方式更容易，并且被认为是非常pythonic的。

Answer 3

使用 while True: 循环。当任何函数中引发异常时，它将自动退出。