Python Standard Error Class
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This module never needs to be imported explicitly: the exceptions are provided in the built-in namespace as well as the python typeerror exceptions module. For class exceptions, in a try
Python Valueerror Example
statement with an except clause that mentions a particular class, that clause also handles any exception python filenotfounderror classes derived from that class (but not exception classes from which it is derived). Two exception classes that are not related via subclassing are never equivalent,
Python Custom Exception
even if they have the same name. The built-in exceptions listed below can be generated by the interpreter or built-in functions. Except where mentioned, they have an "associated value" indicating the detailed cause of the error. This may be a string or a tuple containing several items of information (e.g., an error code and python exception message a string explaining the code). The associated value is the second argument to the raise statement. If the exception class is derived from the standard root class BaseException, the associated value is present as the exception instance's args attribute. 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. The following exceptions are only used as base classes for other exceptions. exception BaseException¶ The base class for all built-in exceptions. It i
you have probably seen some. There are (at least) two distinguishable kinds of errors: syntax errors and exceptions. 8.1. Syntax Errors¶ Syntax errors, also known as parsing errors, are perhaps the most common kind of complaint you get
Python Exception Class Methods
while you are still learning Python: >>> while True print 'Hello world' File "
Python Errno
1 while True print 'Hello world' ^ SyntaxError: invalid syntax The parser repeats the offending line and displays a little ‘arrow' pointing python attributeerror object has no attribute at the earliest point in the line where the error was detected. The error is caused by (or at least detected at) the token preceding the arrow: in the example, the error is detected at the keyword https://docs.python.org/2/library/exceptions.html print, since a colon (':') is missing before it. File name and line number are printed so you know where to look in case the input came from a script. 8.2. Exceptions¶ Even if a statement or expression is syntactically correct, it may cause an error when an attempt is made to execute it. Errors detected during execution are called exceptions and are not unconditionally fatal: you will soon learn how to handle https://docs.python.org/2.7/tutorial/errors.html them in Python programs. Most exceptions are not handled by programs, however, and result in error messages as shown here: >>> 10 * (1/0) Traceback (most recent call last): File "
here for a quick overview of the site Help Center Detailed answers to any questions you might have Meta Discuss the workings and policies of this site About Us Learn more about Stack Overflow the company Business Learn more about http://stackoverflow.com/questions/1319615/proper-way-to-declare-custom-exceptions-in-modern-python hiring developers or posting ads with us Stack Overflow Questions Jobs Documentation Tags Users Badges Ask https://grass.osgeo.org/grass70/manuals/libpython/exceptions.html Question x Dismiss Join the Stack Overflow Community Stack Overflow is a community of 6.2 million programmers, just like you, helping each other. Join them; it only takes a minute: Sign up Proper way to declare custom exceptions in modern Python? up vote 595 down vote favorite 158 What's the proper way to declare custom exception classes in modern Python? My primary python exception goal is to follow whatever standard other exception classes have, so that (for instance) any extra string I include in the exception is printed out by whatever tool caught the exception. By "modern Python" I mean something that will run in Python 2.5 but be 'correct' for the Python 2.6 and Python 3.* way of doing things. And by "custom" I mean an Exception object that can include extra data about the cause of the error: a string, maybe python standard error also some other arbitrary object relevant to the exception. I was tripped up by the following deprecation warning in Python 2.6.2: >>> class MyError(Exception): ... def __init__(self, message): ... self.message = message ... >>> MyError("foo") _sandbox.py:3: DeprecationWarning: BaseException.message has been deprecated as of Python 2.6 It seems crazy that BaseException has a special meaning for attributes named message. I gather from PEP-352 that attribute did have a special meaning in 2.5 they're trying to deprecate away, so I guess that name (and that one alone) is now forbidden? Ugh. I'm also fuzzily aware that Exception has some magic parameter args, but I've never known how to use it. Nor am I sure it's the right way to do things going forward; a lot of the discussion I found online suggested they were trying to do away with args in Python 3. Update: two answers have suggested overriding __init__, and __str__/__unicode__/__repr__. That seems like a lot of typing, is it necessary? python exception share|improve this question edited Jun 5 '12 at 20:37 Eitan T 27.9k113978 asked Aug 23 '09 at 21:29 Nelson 6,43532027 2 *args (or *foo, or *whatever, all that matters is that it has the star in front) is for functions that have an indefinite number of positional arguments. So if you have def myfunction(*args), you can call it like myfunction("foo") or myfunction("foo", "bar") and the arguments will be accessible
and the built-in namespace. It is recommended that user-defined exceptions inherit from Exception. See the documentation for the exception inheritance hierarchy. exception ArithmeticError¶ Bases: exceptions.StandardError Base class for arithmetic errors. exception AssertionError¶ Bases: exceptions.StandardError Assertion failed. exception AttributeError¶ Bases: exceptions.StandardError Attribute not found. exception BaseException¶ Bases: object Common base class for all exceptions args¶ message¶ exception BufferError¶ Bases: exceptions.StandardError Buffer error. exception BytesWarning¶ Bases: exceptions.Warning Base class for warnings about bytes and buffer related problems, mostly related to conversion from str or comparing to str. exception DeprecationWarning¶ Bases: exceptions.Warning Base class for warnings about deprecated features. exception EOFError¶ Bases: exceptions.StandardError Read beyond end of file. exception EnvironmentError¶ Bases: exceptions.StandardError Base class for I/O related errors. errno¶ exception errno filename¶ exception filename strerror¶ exception strerror exception Exception¶ Bases: exceptions.BaseException Common base class for all non-exit exceptions. exception FloatingPointError¶ Bases: exceptions.ArithmeticError Floating point operation failed. exception FutureWarning¶ Bases: exceptions.Warning Base class for warnings about constructs that will change semantically in the future. exception GeneratorExit¶ Bases: exceptions.BaseException Request that a generator exit. exception IOError¶ Bases: exceptions.EnvironmentError I/O operation failed. exception ImportError¶ Bases: exceptions.StandardError Import can't find module, or can't find name in module. exception ImportWarning¶ Bases: exceptions.Warning Base class for warnings about probable mistakes in module imports exception IndentationError¶ Bases: exceptions.SyntaxErr