What is a KeyError Exception? In Python, aKeyErrorexception is one of the built-in exceptions that is designed to handle a wide range of common error conditions. AKeyErrorexception can be understood as a subclass, along withIndexError, of the more generalLookupErrorexception, all of which are...
Although most of the time, a KeyError is raised because of an invalid key in a Python dictionary or a dictionary subclass, you may also find it in other places in the Python Standard Library, such as in a zipfile. However, it denotes the same semantic meaning of the Python KeyError, wh...
What is a KeyError in Python Dictionary? AKeyErrorin Python is raised when a dictionary is accessed with a key that does not exist in that dictionary. Consider the following example: dictionary = {"name": "John", "age": 25} print(dictionary["profession"]) In the above code snippet, try...
defmain():user_input=get_user_input()ifuser_input is None:returnwhileuser_input.strip().lower()=='y':myString=input("What string would you like to reverse?:")ReverseString=myString[::-1]print(("Your Reversed String is %s")%ReverseString)user_input=get_user_input()if__n...
('Give $who $100').substitute(d)Traceback(most recent call last):...ValueError:Invalid placeholderinstring:line1,col11>>>Template('$who likes $what').substitute(d)Traceback(most recent call last):...KeyError:'what'>>>Template('$who likes $what').safe_substitute(d)'tim likes $what'...
如果使用[]查找不存在的key,会引发KeyError的异常。如果使用get方法则不会引起异常,只会得到一个None: # Looking up a non-existing key is a KeyError filled_dict["four"] # KeyError # Use "get()" method to avoid the KeyError filled_dict.get("one") # => 1 ...
如果这个键不存在,将引发 KeyError 异常,而 except 子句 将捕获这个异常。 你可能发现,检查对象是否包含特定的属性时, try / except 也很有用。例如,假设你要检查 一个对象是否包含属性 write ,可使用类似于下面的代码: try: obj.write except AttributeError: print('The object is not writeable') else: ...
KeyError: 'what' >>> Template('$who likes $what').safe_substitute(d) 'tim likes $what' 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 进阶用法:你可以派生 Template 的子类来自定义占位符语法、分隔符,或用于解析模板字符串的整个正则表达式。 为此目的,你可以重载这些...
KeyError映射(比如字典)中的键不存在 AttributeError属性错误(对象无指定名字的属性) TypeError 类型出错 SyntaxError代码语法错误 OSError操作系统未能执行指定任务 ZeroDivisionError 除0错误 这些异常类,都继承自Exception类型。在本书的前半部分,我们对于这些异常采取了放任的态度: 程序直接报错停止。但一个严谨的程序,应...
sys():i ==:KeyError()i ==:ValueError()(): exception =: bar((sys.argv[]))KeyErrore: exception = e()ValueErrore: exception = e()(exception) good() Running this on Py3k: $ python3 foo.py 1 keyerror1 $ python3 foo.py 2 valueerror2 ...