Python Runtime Error Type Exceptions Assertionerror
Contents |
a try statement with an except clause that mentions a particular class, that clause also handles any exception classes derived from type error python that class (but not exception classes from which it is derived). Two python custom exception exception classes that are not related via subclassing are never equivalent, even if they have the same name. python exception message 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 python filenotfounderror 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. 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
Python Valueerror Example
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 raise to re-raise the exception currently being handled), the implicit exception context can be supplemented with an explicit cause by using from with raise: raise new_exc from original_exc The expression following from must be an exception or None. It will be set as __cause__ on t
Exception StandardError ArithmeticError LookupError EnvironmentError Raised Exceptions AssertionError AttributeError EOFError FloatingPointError GeneratorExit IOError ImportError IndexError KeyError KeyboardInterrupt MemoryError NameError NotImplementedError
Python Exception Class Methods
OSError OverflowError ReferenceError RuntimeError StopIteration SyntaxError SystemError SystemExit TypeError UnboundLocalError UnicodeError python 3 exceptions ValueError ZeroDivisionError Warning Categories Navigation Table of Contents Previous: Built-in Objects Next: String Services This Page Show Source python errno 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 https://docs.python.org/3/library/exceptions.html 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 https://pymotw.com/2/exceptions/ 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.
exceptions. Exception All built-in, non-system-exiting exceptions are derived from this class. All user-defined exceptions should also be derived from this class. StandardError http://www.pythonforbeginners.com/error-handling/pythons-built-in-exceptions The base class for all built-in exceptions except StopIteration, GeneratorExit, KeyboardInterrupt and SystemExit. StandardError itself is derived fromException. ArithmeticError The base class for those built-in exceptions that http://www.jython.org/jythonbook/en/1.0/ExceptionHandlingDebug.html are raised for various arithmetic errors: OverflowError, ZeroDivisionError, FloatingPointError LookupError The base class for the exceptions that are raised when a key or index used on a python exception mapping or sequence is invalid: IndexError, KeyError. This can be raised directly by sys.setdefaultencoding() EnvironmentError The base class for exceptions that can occur outside the Python system: IOError, OSError. AssertionError Raised when an assert statement fails. AttributeError Raised when an attribute reference or assignment fails. EOFError Raised when one of the built-in functions (input() or python runtime error raw_input()) hits an end-of-file condition (EOF) without reading any data. FloatingPointError Raised when a floating point operation fails. GeneratorExit Raise when a generator's close() method is called. It directly inherits from Exception instead of StandardError since it is technically not an error. IOError Raised when an I/O operation (such as a print statement, the built-in open() function or a method of a file object) fails for an I/O-related reason, e.g., ``file not found'' or ``disk full''. This class is derived from EnvironmentError. ImportError Raised when an import statement fails to find the module definition or when a from...import fails to find a name that is to be imported. IndexError Raised when a sequence subscript is out of range. KeyError Raised when a mapping (dictionary) key is not found in the set of existing keys. KeyboardInterrupt Raised when the user hits the interrupt key (normally Control-C or Delete). MemoryError Raised when an operation runs out of memory but the situation may
end-user then by having them run into an issue with your software and displaying a big ugly error message on the screen, followed by a program crash. Exception handling is all about ensuring that when your program encounters an issue, it will continue to run and provide informative feedback to the end-user or program administrator. Any Java programmer becomes familiar with exception handling on day one, as some Java code won’t even compile unless there is some form of exception handling put into place via the try-catch-finally syntax. Python has similar constructs to that of Java, and we’ll discuss them in this chapter. After you have found an exception, or preferably before your software is distributed, you should go through the code and debug it in order to find and repair the erroneous code. There are many different ways to debug and repair code; we will go through some debugging methodologies in this chapter. In Python as well as Java, the assert keyword can help out tremendously in this area. We’ll cover assert in depth here and learn the different ways that it can be used to help you out and save time debugging those hard-to-find errors. Exception Handling Syntax and Differences with Java¶ Java developers are very familiar with the try-catch-finally block as this is the main mechanism that is used to perform exception handling. Python exception handling differs a bit from Java, but the syntax is fairly similar. However, Java differs a bit in the way that an exception is thrown in code. Now, realize that I just used the term throw…this is Java terminology. Python does not throw exceptions, but instead it raises them. Two different terms which mean basically the same thing. In this section, we’ll step through the process of handling and raising exceptions in Python code, and show you how it differs from that in Java. For those who are unfamiliar, I will show you how to perform some exception handling in the Java language. This will give you an opportunity to compare the two syntaxes and appreciate the flexibility that Python offers. Listing 7-1. Exception Handling in Java try { // perform some tasks that may throw an exception } catch (ExceptionType messageVariable) { // perform some exception handling } fin