Python Unimplemented Error
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a try statement with an except clause that mentions a particular class, that python filenotfounderror clause also handles any exception classes derived from that class python custom exception (but not exception classes from which it is derived). Two exception classes that are not python exception message related via subclassing are never equivalent, even if they have the same name. The built-in exceptions listed below can be generated by the interpreter or built-in
Python Exception Class Methods
functions. Except where mentioned, they have an "associated value" indicating the detailed cause of the error. This may be a string or a tuple of several items of information (e.g., an error code and a string explaining the code). The associated value is usually passed as arguments to the exception class's constructor. python 3 exceptions User code can raise built-in exceptions. This can be used to test an exception handler or to report an error condition "just like" the situation in which the interpreter raises the same exception; but beware that there is nothing to prevent user code from raising an inappropriate error. The built-in exception classes can be subclassed to define new exceptions; programmers are encouraged to derive new exceptions from the Exception class or one of its subclasses, and not from BaseException. More information on defining exceptions is available in the Python Tutorial under User-defined Exceptions. When raising (or re-raising) an exception in an except or finally clause __context__ is automatically set to the last exception caught; if the new exception is not handled the traceback that is eventually displayed will include the originating exception(s) and the final exception. When raising a new exception (rather than using a bare
is to be a return value python errno for rich comparison methods such as __eq__() and __lt__(),
Python Attributeerror Object Has No Attribute
which indicates the type on which these methods exist cannot be compared in
Assertionerror Python
that manner, e.g.: class Foo: def __lt__(self, obj): return https://docs.python.org/3/library/exceptions.html class="bp">NotImplemented print(Foo() < Foo()) Which yields: Traceback (most recent call last): File "test.py", line 5, in
here for a quick overview of the site Help Center Detailed answers to any questions you might have Meta Discuss http://stackoverflow.com/questions/878943/why-return-notimplemented-instead-of-raising-notimplementederror the workings and policies of this site About Us Learn more https://pymotw.com/2/exceptions/ about Stack Overflow the company Business Learn more about hiring developers or posting ads with us Stack Overflow Questions Jobs Documentation Tags Users Badges Ask Question x Dismiss Join the Stack Overflow Community Stack Overflow is a community of 6.2 million programmers, just like you, helping each python exception other. Join them; it only takes a minute: Sign up Why return NotImplemented instead of raising NotImplementedError up vote 134 down vote favorite 24 Python has a singleton called NotImplemented. Why would someone want to ever return NotImplemented instead of raising the NotImplementedError exception? Won't it just make it harder to find bugs, such as code that executes python unimplemented error invalid methods? python share|improve this question edited Jul 31 at 7:53 Fermi paradox 2,18241543 asked May 18 '09 at 17:43 abyx 29k1268101 add a comment| 3 Answers 3 active oldest votes up vote 149 down vote accepted It's because __lt__() and related comparison methods are quite commonly used indirectly in list sorts and such. Sometimes the algorithm will choose to try another way or pick a default winner. Raising an exception would break out of the sort unless caught, whereas NotImplemented doesn't get raised and can be used in further tests. http://jcalderone.livejournal.com/32837.html To summarise that link: "NotImplemented signals to the runtime that it should ask someone else to satisfy the operation. In the expression a == b, if a.__eq__(b) returns NotImplemented, then Python tries b.__eq__(a). If b knows enough to return True or False, then the expression can succeed. If it doesn't, then the runtime will fall back to the built-in behavior (which is based on identity for == and !=)." share|improve this answer edited Jul 31 at 7:55 Fermi paradox 2
Exception StandardError ArithmeticError LookupError EnvironmentError Raised Exceptions AssertionError AttributeError EOFError FloatingPointError GeneratorExit IOError ImportError IndexError KeyError KeyboardInterrupt MemoryError NameError NotImplementedError OSError OverflowError ReferenceError RuntimeError StopIteration SyntaxError SystemError SystemExit TypeError UnboundLocalError UnicodeError ValueError ZeroDivisionError Warning Categories Navigation Table of Contents Previous: Built-in Objects Next: String Services This Page Show Source Examples The output from all the example programs from PyMOTW has been generated with Python 2.7.8, unless otherwise noted. Some of the features described here may not be available in earlier versions of Python. If you are looking for examples that work under Python 3, please refer to the PyMOTW-3 section of the site. Navigation index modules | next | previous | PyMOTW » Built-in Objects » exceptions - Built-in error classes¶ Purpose:The exceptions module defines the built-in errors used throughout the standard library and by the interpreter. Available In:1.5 and later Description¶ In the past, Python has supported simple string messages as exceptions as well as classes. Since 1.5, all of the standard library modules use classes for exceptions. Starting with Python 2.5, string exceptions result in a DeprecationWarning, and support for string exceptions will be removed in the future. Base Classes¶ The exception classes are defined in a hierarchy, described in the standard library documentation. In addition to the obvious organizational benefits, exception inheritance is useful because related exceptions can be caught by catching their base class. In most cases, these base classes are not intended to be raised directly. BaseException¶ Base class for all exceptions. Implements logic for creating a string representation of the exception using str() from the arguments passed to the constructor. Exception¶ Base class for exceptions that do not result in quitting the running application. All user-defined exceptions should use Exception as a base class. StandardError¶ Base class for built-in exceptions used in the standard library. ArithmeticError¶ Base class for math-related errors. LookupError¶ Base class for errors raised when something can't be found. EnvironmentError¶ Base class for errors that come