像大多数现代编程语言一样，Python不支持“ goto”。而是必须使用控制功能。基本上有两种方法可以做到这一点。

1.循环

您可以如何完全按照SmallBasic示例进行操作的示例如下：

while True :    print "Poo"

就这么简单。

2.递归

def the_func() :   print "Poo"   the_func()the_func()

关于递归的注意事项：仅当您有特定次数要返回到开始时才执行此操作（在这种情况下，添加递归应停止的情况）。像我在上面定义的那样进行无限递归是一个坏主意，因为您最终将耗尽内存！

编辑以更具体地回答问题

#Alan's Toolkit for conversionsinvalid_input = Truedef start() :    print ("Welcome to the converter toolkit made by Alan.")    op = input ("Please input what operation you wish to perform. 1 for Fahrenheit to Celsius, 2 for meters to centimetres and 3 for megabytes to gigabytes")    if op == "1":        #stuff        invalid_input = False # Set to False because input was valid    elif op == "2":        #stuff        invalid_input = False # Set to False because input was valid    elif op == "3": # you still have this as "if"; I would recommend keeping it as elif        #stuff        invalid_input = False # Set to False because input was valid    else:        print ("Sorry, that was an invalid command!")while invalid_input : # this will loop until invalid_input is set to be True    start()