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you have probably seen some. There are (at least) two distinguishable kinds of errors: syntax errors and exceptions. 8.1. python raise custom exception Syntax Errors¶ Syntax errors, also known as parsing errors, are perhaps python error types the most common kind of complaint you get while you are still learning Python: >>> while True python raise valueerror print 'Hello world' File "", line 1 while True print 'Hello world' ^ SyntaxError: invalid syntax The parser repeats the offending line and displays a little ‘arrow' pointing

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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 print, since a colon (':') is missing before it. File name and line number are printed so syntax for raise clause in python 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 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 "", line 1, in ZeroDivisionError: integer division or modulo by zero >>> 4 + spam*3 Traceback (most recent call last): File "", line 1, in NameError: name 'spam' is not defined >>> '2' + 2 Traceback (most recent call last): File "", line 1, in TypeError: cannot concatenate 'str' and 'int' objects The last line of the error message indicates what happened. Exceptions come in different types, and the type is printed as part of the message: th

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Is Nested Try Block Possible In Python

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like you, helping each other. Join them; it only takes a minute: Sign up Manually raising (throwing) an exception in Python up vote 800 down vote favorite 189 How can I raise an exception in Python so https://docs.python.org/2.7/tutorial/errors.html that it can later be caught via an except block? python exception exception-handling share|improve this question edited Feb 3 '15 at 14:37 DavidRR 5,20472747 asked Jan 12 '10 at 21:07 TIMEX 41.2k201525826 add a comment| 3 Answers 3 active oldest votes up vote 787 down vote accepted How do I manually throw/raise an exception in Python? Use the most specific Exception constructor that semantically fits your issue. Be specific in your message, e.g.: raise http://stackoverflow.com/questions/2052390/manually-raising-throwing-an-exception-in-python ValueError('A very specific bad thing happened') Don't do this: Avoid raising a generic Exception, to catch it, you'll have to catch all other more specific exceptions that subclass it. Hiding bugs raise Exception('I know Python!') # don't, if you catch, likely to hide bugs. For example: def demo_bad_catch(): try: raise ValueError('represents a hidden bug, do not catch this') raise Exception('This is the exception you expect to handle') except Exception as error: print('caught this error: ' + repr(error)) >>> demo_bad_catch() caught this error: ValueError('represents a hidden bug, do not catch this',) Won't catch and more specific catches won't catch the general exception: def demo_no_catch(): try: raise Exception('general exceptions not caught by specific handling') except ValueError as e: print('we will not catch e') >>> demo_no_catch() Traceback (most recent call last): File "", line 1, in File "", line 3, in demo_no_catch Exception: general exceptions not caught by specific handling Best Practice: Instead, use the most specific Exception constructor that semantically fits your issue. raise ValueError('A very specific bad thing happened') which also handily allows an arbitrary number of arguments to be passed to the constructor. This works in Python 2 and 3. raise ValueError('A very specific bad thing happened', 'foo', 'bar', 'baz') These arguments are accessed by the args attribute on the Exception object. For example: try: some_code_that_may_raise_our_value_error() except ValueError as err: print(err.

here for a quick overview of the site Help Center Detailed answers to any questions you might have Meta Discuss http://stackoverflow.com/questions/6020450/oracle-pl-sql-raise-user-defined-exception-with-custom-sqlerrm the workings and policies of this site About Us Learn more about Stack Overflow the company Business Learn more about hiring developers or posting ads with us Stack Overflow Questions http://www.linuxtopia.org/online_books/programming_books/introduction_to_python/python_tut_64.html 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 other. python raise Join them; it only takes a minute: Sign up Oracle PL/SQL - Raise User-Defined Exception With Custom SQLERRM up vote 45 down vote favorite 21 Is it possible to create user-defined exceptions and be able to change the SQLERRM? For example: DECLARE ex_custom EXCEPTION; BEGIN RAISE ex_custom; EXCEPTION WHEN ex_custom THEN DBMS_OUTPUT.PUT_LINE(SQLERRM); END; / The output is "User-Defined clause in python Exception". Is it possible to change that message? EDIT: Here is some more detail. I hope this one illustrates what I'm trying to do better. DECLARE l_table_status VARCHAR2(8); l_index_status VARCHAR2(8); l_table_name VARCHAR2(30) := 'TEST'; l_index_name VARCHAR2(30) := 'IDX_TEST'; ex_no_metadata EXCEPTION; BEGIN BEGIN SELECT STATUS INTO l_table_status FROM USER_TABLES WHERE TABLE_NAME = l_table_name; EXCEPTION WHEN NO_DATA_FOUND THEN -- raise exception here with message saying -- "Table metadata does not exist." RAISE ex_no_metadata; END; BEGIN SELECT STATUS INTO l_index_status FROM USER_INDEXES WHERE INDEX_NAME = l_index_name; EXCEPTION WHEN NO_DATA_FOUND THEN -- raise exception here with message saying -- "Index metadata does not exist." RAISE ex_no_metadata; END; EXCEPTION WHEN ex_no_metadata THEN DBMS_OUTPUT.PUT_LINE('Exception will be handled by handle_no_metadata_exception(SQLERRM) procedure here.'); DBMS_OUTPUT.PUT_LINE(SQLERRM); END; / In reality, there are dozens of those sub-blocks. I'm wondering if there's a way to have a single user-defined exception for each of those sub-blocks to raise, but have it give a different message, instead of creating a separate user-defined exception for each sub-block. In .NET, it would be sort of like having a custom exce

Web Development GUI Toolkits/Desktop Databases Mail Systems openSolaris Eclipse Documentation Techotopia.com Virtuatopia.com How To Guides Virtualization General System Admin Linux Security Linux Filesystems Web Servers Graphics & Desktop PC Hardware Windows Problem Solutions <<< previous table of contents next >>> 10.5 User-defined Exceptions Programs may name their own exceptions by creating a new exception class. Exceptions should typically be derived from the Exception class, either directly or indirectly. For example: >>> class MyError(Exception): ... def __init__(self, value): ... self.value = value ... def __str__(self): ... return `self.value` ... >>> try: ... raise MyError(2*2) ... except MyError, e: ... print 'My exception occurred, value:', e.value ... My exception occurred, value: 4 >>> raise MyError, 'oops!' Traceback (most recent call last): File "", line 1, in ? __main__.MyError: 'oops!' Exception classes can be defined which do anything any other class can do, but are usually kept simple, often only offering a number of attributes that allow information about the error to be extracted by handlers for the exception. When creating a module which can raise several distinct errors, a common practice is to create a base class for exceptions defined by that module, and subclass that to create specific exception classes for different error conditions: class Error(Exception): """Base class for exceptions in this module.""" pass class InputError(Error): """Exception raised for errors in the input. Attributes: expression -- input expression in which the error occurred message -- explanation of the error """ def __init__(self, expression, message): self.expression = expression self.message = message class TransitionError(Error): """Raised when an operation attempts a state transition that's not allowed. Attributes: previous -- state at beginning of transition next -- attempted new

 

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