除了字母和数字外，我如何正确地循环

Question

我有一个运行良好的程序。现在，我将错误检查添加到所有输入中。

如何在函数add_one_item中循环new_name输入和new_qty输入？

当前打印错误消息，但不会再次循环输入。如果为名称输入3，则会打印错误消息，但会移动到qty字段。我该如何解决这个问题？

谢谢你抽出时间。

代码：

import os
class Inventory:
def __init__(self):
self.item = []
self.qty = []
def remove(self, name):
ix = self.item.index(name)
self.item.pop(ix)
self.qty.pop(ix)
def add(self, name, qty):
self.item.append(name)
self.qty.append(qty)
def update(self, name, update):
if update >= 0:
self.qty[self.item.index(name)] += update
elif update <= -1:
self.qty[self.item.index(name)] += update
def search(self, name):
pos = self.item.index(name) if name in self.item else -1
if pos >= 0:
return self.item[pos], self.qty[pos]
else:
return None
def __str__(self):
out = ""
zipo = list(zip(self.item, self.qty))
for foobar in zipo:
out += f"Item : {foobar[0]} nQuantity : {foobar[1]}n"
out += "----------n"
return out

def menuDisplay():
"""Display the menu"""
print('=============================')
print('= Inventory Management Menu =')
print('=============================')
print('(1) Add New Item to Inventory')
print('(2) Remove Item from Inventory')
print('(3) Update Inventory')
print('(4) Search Item in Inventory')
print('(5) Print Inventory Report')
print('(99) Quit')

def add_one_item(inventory):
print('Adding Inventory')
print('================')
while True:
try:
new_name = input('Enter the name of the item: ')
if not new_name.isalpha():
print("Only letters are allowed!")
print()
new_qty = int(input("Enter the quantity of the item: "))
inventory.add(new_name, new_qty)
break
except Exception as e:
print("Invalid choice! try again! " + str(e))
print()
continue

def remove_one_item(inventory):
print('Removing Inventory')
print('==================')
removing = input('Enter the item name to remove from inventory: ')
inventory.remove(removing)

def ask_exit_or_continue():
return int(input('Enter 98 to continue or 99 to exit: '))

def update_inventory(inventory):
print('Updating Inventory')
print('==================')
item = input('Enter the item to update: ')
update = int(input(
"Enter the updated quantity. Enter 5 for additional or -5 for less: "))
inventory.update(item, update)

def search_inventory(inventory):
print('Searching Inventory')
print('===================')
search = input('Enter the name of the item: ')
result = inventory.search(search)
if result is None:
print("Item not in inventory")
else:
name, qty = result
print('Item:     ', name)
print('Quantity: ', qty)
print('----------')

def print_inventory(inventory):
print('Current Inventory')
print('=================')
print(inventory)

def main():
inventory = Inventory()
while True:
try:
menuDisplay()
CHOICE = int(input("Enter choice: "))
if CHOICE in [1, 2, 3, 4, 5]:
if CHOICE == 1:
add_one_item(inventory)
elif CHOICE == 2:
remove_one_item(inventory)
elif CHOICE == 3:
update_inventory(inventory)
elif CHOICE == 4:
search_inventory(inventory)
elif CHOICE == 5:
print_inventory(inventory)
exit_choice = ask_exit_or_continue()
if exit_choice == 99:
exit()
elif CHOICE == 99:
exit()
except Exception as e:
print("Invalid choice! try again!"+str(e))
print()
# If the user pick an invalid choice,
# the program will come to here and
# then loop back.

main()

Answer 1

由于您已经设置了一个循环，如果出现异常，该循环将继续，因此一个简单的解决方案是在名称包含非字母时引发异常：

def add_one_item(inventory):
print('Adding Inventory')
print('================')
while True:
try:
new_name = input('Enter the name of the item: ')
assert new_name.isalpha(), "Only letters are allowed!"
new_qty = int(input("Enter the quantity of the item: "))
inventory.add(new_name, new_qty)
break
except Exception as e:
print(f"Invalid choice! try again! {e}n")

这使得try/except在许多情况下比使用if/else检查错误条件更好——您可以非常干净地让一个except处理来自多个不同地方的异常，并且您可以决定什么是异常，什么不是异常！在这种情况下，如果输入与您的要求不匹配，assert将引发异常，就像如果输入不是有效的整数字符串，int()函数将引发异常一样。

请注意，在循环体的末尾不需要continue；它将自动继续，除非您使用break或return。

Answer 2

您需要分离while循环才能最干净地工作：

while True:
x = input("...")
if x.isalpha():
break
print("error message")
while True:
try:
y = int(input("..."))
break
except ValueError as e:
print("error message")