'None' 从调用“.get()”问题返回

Question

从对 .get() 的调用中获取 None returned 可能意味着未找到该键或者在字典中找到的键值实际上是 None.

那么，如果在布尔测试中没有找到并且解释为 0，我可以将 return 值设置为什么？

写这个：

ages = {'Jim': 30, 'Pam': 28, 'Kevin': None}
person = input('Get age for: ')
age = ages.get(person, ?) #what need to be '?'

if age:
    print(f'{person} is {age} years old.')
else:
    print(f"{person}'s age is unknown.")

Answer 1

您不需要使用 .get。直接访问字典值即可。

像这样：

ages = {'Jim': 30, 'Pam': 28, 'Kevin': None}
person = input('Get age for: ')

try:
    age = ages[person]
    
    if age:
        print(f'{person} is {age} years old.')
    else:
        print(f"{person}'s age is unknown.")
except KeyError:
    print(f"Unknown person: {person}")

Answer 2

在这种情况下，使用 try/except:

会很有用

ages = {'Jim': 30, 'Pam': 28, 'Kevin': None}
person = input('Get age for: ')
try:
    age = ages[person] #what need to be '?'
    if age:
        print(f'{person} is {age} years old.')
    else:
        print(f"{person}'s age is unknown.")
except KeyError:
    print(f'{person} not found in ages')

输出

Get age for: Jim
Jim is 30 years old.

Get age for: Kevin
Kevin's age is unknown.

Get age for: Bob
Bob not found in ages

Answer 3

ages = {'Jim': 30, 'Pam': 28, 'Kevin': None}
person = input('Get age for: ')

try:
    age = ages[person]
    
    if age:
        print(f'{person} is {age} years old.')
    else:
        print(f"{person}'s age is unknown.")
except KeyError:
    print(f"{person} is not known.")

'None' 从调用“.get()”问题返回

'None' returned from a call to '.get()' issue

python

mapping

dictionary

nonetype