在 Python 字典中找不到 key 时抛出什么异常？
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What exception is thrown when key is not found in Python dictionary?
提问by sivabudh
If I have:
如果我有：
map = { 'stack':'overflow' }
try:
map['experts-exchange']
except: <--- What is the Exception type that's thrown here?
print( 'is not free' )
Couldn't find it on the web. =(
在网上找不到它。=（
采纳答案by fabrizioM
KeyError
if you do it on the console without the try block will tell it to you
如果你在没有 try 块的控制台上执行它会告诉你
>>> a = {}
>>> a['invalid']
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
KeyError: 'invalid'
>>>
回答by John Ledbetter
Python 2.6.6 (r266:84292, Sep 15 2010, 16:22:56)
[GCC 4.4.5] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> map = { 'a' : 'b' }
>>> print map['c']
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
KeyError: 'c'
>>>
So a wild guess might be...a KeyError?
所以一个疯狂的猜测可能是...a KeyError?
回答by anijhaw
Its called KeyError
它叫做KeyError
>>d={1:2}
>>d[2]
Traceback (most recent call last):
File "<stdin>", line 1, in ?
KeyError: 2
回答by user225312
KeyError.
KeyError.
>>> x = {'try': 1, 'it': 2}
>>> x['wow']
Traceback (most recent call last):
File "<pyshell#3>", line 1, in <module>
x['wow']
KeyError: 'wow'
回答by Kushan Gunasekera
If you don't know the specific exception to handle, you can simply do this kind of thing,
如果你不知道具体要处理的异常，你可以简单地做这种事情，
map = {'stack': 'overflow'}
try:
map['experts-exchange']
except Exception as inst:
print(type(inst)) # the exception instance
print(inst.args) # arguments stored in .args
print(inst) # __str__ allows args to be printed directly,
# but may be overridden in exception subclasses
The out put of the above code is,
上面代码的输出是，
<class 'KeyError'>
('experts-exchange',)
'experts-exchange'
When an exception occurs, it may have an associated value, also known as the exception's argument. The presence and type of the argument depend on the exception type.
当异常发生时，它可能有一个关联的值，也称为异常的参数。参数的存在和类型取决于异常类型。
The except clause may specify a variable after the exception name. The variable is bound to an exception instance with the arguments stored in instance.args. For convenience, the exception instance defines __str __()so the arguments can be printed directly without having to reference .args. One may also instantiate an exception first before raising it and add any attributes to it as desired.
except 子句可以在异常名称之后指定一个变量。该变量绑定到一个异常实例，参数存储在 instance.args 中。为方便起见，异常实例定义了__str __()以便可以直接打印参数而无需引用 .args。也可以在引发异常之前先实例化异常，并根据需要向其添加任何属性。
