我在想办法让 Python 回到代码的顶部。在 SmallBasic,你做
start:
textwindow.writeline("Poo")
goto start
但我不知道你是如何在 Python 中做到这一点的:/有任何想法吗?
我要循环的代码是这样的
#Alan's Toolkit for conversions
def 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":
f1 = input ("Please enter your fahrenheit temperature: ")
f1 = int(f1)
a1 = (f1 - 32) / 1.8
a1 = str(a1)
print (a1+" celsius")
elif op == "2":
m1 = input ("Please input your the amount of meters you wish to convert: ")
m1 = int(m1)
m2 = (m1 * 100)
m2 = str(m2)
print (m2+" m")
if op == "3":
mb1 = input ("Please input the amount of megabytes you want to convert")
mb1 = int(mb1)
mb2 = (mb1 / 1024)
mb3 = (mb2 / 1024)
mb3 = str(mb3)
print (mb3+" GB")
else:
print ("Sorry, that was an invalid command!")
start()
所以基本上,当用户完成他们的转换时,我希望它循环回到顶部。我仍然无法将您的循环示例付诸实践,因为每次我使用 def 函数进行循环时,它都会说“op”未定义。
使用无限循环:
while True:
print('Hello world!')
这当然也适用于您的
start()
功能;您可以使用 break
退出循环,或者使用 return
完全退出函数,这也会终止循环:
def start():
print ("Welcome to the converter toolkit made by Alan.")
while True:
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":
f1 = input ("Please enter your fahrenheit temperature: ")
f1 = int(f1)
a1 = (f1 - 32) / 1.8
a1 = str(a1)
print (a1+" celsius")
elif op == "2":
m1 = input ("Please input your the amount of meters you wish to convert: ")
m1 = int(m1)
m2 = (m1 * 100)
m2 = str(m2)
print (m2+" m")
if op == "3":
mb1 = input ("Please input the amount of megabytes you want to convert")
mb1 = int(mb1)
mb2 = (mb1 / 1024)
mb3 = (mb2 / 1024)
mb3 = str(mb3)
print (mb3+" GB")
else:
print ("Sorry, that was an invalid command!")
如果您还要添加一个退出选项,那可能是:
if op.lower() in {'q', 'quit', 'e', 'exit'}:
print("Goodbye!")
return
例如。
Python 和大多数现代编程语言一样,不支持“goto”。相反,您必须使用控制功能。基本上有两种方法可以做到这一点。
1。循环
您如何完全按照您的 SmallBasic 示例执行操作的示例如下:
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:仅当您想要返回开头的特定次数时才这样做(在这种情况下添加递归应该停止的情况)。像我上面定义的那样进行无限递归是个坏主意,因为你最终会耗尽内存!
#Alan's Toolkit for conversions
invalid_input = True
def 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 False
start()
你可以很容易地用循环来做,有两种类型的循环
For循环:
for i in range(0,5):
print 'Hello World'
While循环:
count = 1
while count <= 5:
print 'Hello World'
count += 1
这些循环中的每一个都打印“Hello World”五次
Python 有控制流语句而不是
goto
语句。控制流的一种实现是 Python 的while
循环。您可以给它一个布尔条件(布尔值在 Python 中为 True 或 False),循环将重复执行,直到该条件变为 false。如果你想永远循环,你所要做的就是开始一个无限循环。
如果您决定运行以下示例代码,请小心。如果您想终止进程,请在运行时在 shell 中按 Control+C。请注意,该进程必须在前台才能工作。
while True:
# do stuff here
pass
# do stuff here
行只是一条评论。它不执行任何操作。 pass
只是 python 中的一个占位符,基本上说“嗨,我是一行代码,但请跳过我,因为我什么都没做。”
现在假设您想永远重复要求用户输入,并且只有在用户输入字符“q”退出时才退出程序。
你可以这样做:
while True:
cmd = raw_input('Do you want to quit? Enter \'q\'!')
if cmd == 'q':
break
cmd
将只存储用户输入的任何内容(系统将提示用户输入内容并按回车键)。如果 cmd
只存储字母“q”,代码将强制 break
跳出它的封闭循环。 break
语句可以让你跳出任何类型的循环。甚至无限!如果您想编写经常在无限循环中运行的用户应用程序,那么了解它非常有用。如果用户没有准确键入字母“q”,系统将不断重复提示用户,直到进程被强行终止,或者用户决定他已经受够了这个烦人的程序,只想退出。
编写一个 for 或 while 循环并将所有代码放入其中? Goto 类型编程已成为过去。
你需要使用一个while循环。如果你做一个while循环,循环之后没有任何指令,它就会变成一个无限循环,直到你手动停止它才会停止。
def start():
Offset = 5
def getMode():
while True:
print('Do you wish to encrypt or decrypt a message?')
mode = input().lower()
if mode in 'encrypt e decrypt d'.split():
return mode
else:
print('Please be sensible try just the lower case')
def getMessage():
print('Enter your message wanted to :')
return input()
def getKey():
key = 0
while True:
print('Enter the key number (1-%s)' % (Offset))
key = int(input())
if (key >= 1 and key <= Offset):
return key
def getTranslatedMessage(mode, message, key):
if mode[0] == 'd':
key = -key
translated = ''
for symbol in message:
if symbol.isalpha():
num = ord(symbol)
num += key
if symbol.isupper():
if num > ord('Z'):
num -= 26
elif num < ord('A'):
num += 26
elif symbol.islower():
if num > ord('z'):
num -= 26
elif num < ord('a'):
num += 26
translated += chr(num)
else:
translated += symbol
return translated
mode = getMode()
message = getMessage()
key = getKey()
print('Your translated text is:')
print(getTranslatedMessage(mode, message, key))
if op.lower() in {'q', 'quit', 'e', 'exit'}:
print("Goodbye!")
return