1

挑战是通过添加让用户输入名称并取回祖父的选项来改进先前的挑战“谁是你的爸爸”（参见我的成功代码： http: //pastebin.com/AU2aRWHk ）。程序仍然应该只使用一本父子对的字典。

我不能让它工作。到目前为止，我的整个代码都可以在以下位置看到： http: //pastebin.com/33KrEMhT

我显然让这种方式变得比它需要的更困难，现在我被困在一个复杂的世界中。这是我 F'd up 的代码：

# create dictionary
paternal_pairs ={"a": "b",
                 "b": "c",
                 "c": "d"}

# initialize variables
choice = None

# program's user interface
while choice != 0:
print(
"""
   Who's Yo Daddy:

   2 - Look Up Grandfather of a Son
   """
)

choice = input("What would you like to do?: ")
print() 

    # look up grandfather of a son
    if choice == "2":
        son = input("What is the son's name?: ")
        # verify input exists in dictionary
        if son in paternal_pairs.values():
            for dad, boy in paternal_pairs.items():
                if dad == son:
                    temp_son = dad
                    for ol_man, kid in paternal_pairs.items():
                        if temp_son == kid:
                            print("\nThe grandfather of", son, "is", ol_man)
                        else:
                            print("\nNo grandfather listed for", son)
                else:
                    print("\nNo grandfather listed for", son)
        # if input does not exist in dictionary:
        else:
            print("Sorry, that son is not listed. Try adding a father-son pair.")

选择“2”后，我的输出：

What is the son's name?: d

No grandfather listed for d

No grandfather listed for d

No grandfather listed for d

No grandfather listed for d

No grandfather listed for d

No grandfather listed for d

No grandfather listed for d

No grandfather listed for d

显然暂时被困在一个小循环中，它不起作用。所有其他代码都按预期工作。帮助！

4

1 回答 1

4

您遍历字典中的每个条目，并匹配该值，如果它不匹配，那么对于您打印的每个键值对它不匹配。

它等效于以下简化循环：

>>> for i in range(3):
...     if i == 5:
...         print(i)
...     else:
...         print('Not 5')
... 
Not 5
Not 5
Not 5

请改用循环的else:子句，for只有在完成所有值的遍历后才会调用它；break如果找到匹配项，请使用 a ：

for ol_man, kid in paternal_pairs.items():
    if temp_son == kid:
        print("\nThe grandfather of", son, "is", ol_man)
        break
else:
    print("\nNo grandfather listed for", son)

与循环else:一起使用时子句如何工作的小演示：for

>>> for i in range(3):
...     if i == 1:
...         print(i)
...         break
... else:
...     print('Through')
... 
1
>>> for i in range(3):
...     if i == 5:
...         print(i)
...         break
... else:
...     print('Through')
... 
Through

在第一个示例中，我们使用 a 跳出循环break，但在第二个示例中，我们从未到达break语句（i从不等于5），因此到达并打印了else:子句。Through

于 2012-11-13T17:19:10.750 回答