Python Exceptions Error Handling
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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 while python exception message you are still learning Python: >>> while True print 'Hello world' File "
Python Print Exception
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
Python Try Without Except
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 them in Python programs. syntax for generic except clause in python 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 "
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how to handle those. Exception handling allows us to continue our program (or terminate it) if an exception occurs. Error Handling Error handling in Python is done through the use of exceptions http://www.pythonforbeginners.com/error-handling/python-try-and-except that are caught in try blocks and handled in except blocks. Try and Except If http://www.pythonforbeginners.com/error-handling/exception-handling-in-python an error is encountered, a try block code execution is stopped and transferred down to the except block. In addition to using an except block after the try block, you can also use the finally block. The code in the finally block will be executed regardless of whether an exception occurs. Raising an Exception You can raise python exception an exception in your own program by using the raise exception [, value] statement. Raising an exception breaks current code execution and returns the exception back until it is handled. Example A try block look like below try: print "Hello World" except: print "This is an error message!" Exception Errors Some of the common exception errors are: IOError If the file cannot be opened. ImportError If python cannot find the module ValueError Raised python exceptions error when a built-in operation or function receives an argument that has the right type but an inappropriate value KeyboardInterrupt Raised when the user hits the interrupt key (normally Control-C or Delete) EOFError Raised when one of the built-in functions (input() or raw_input()) hits an end-of-file condition (EOF) without reading any data Example Let's have a look at some examples using exceptions. except IOError: print('An error occured trying to read the file.') except ValueError: print('Non-numeric data found in the file.') except ImportError: print "NO module found" except EOFError: print('Why did you do an EOF on me?') except KeyboardInterrupt: print('You cancelled the operation.') except: print('An error occured.') There are a number of built-in exceptions in Python. Recommended Python Training – Treehouse For Python training, our top recommendation is Treehouse. Treehouse is an online training service that teaches web design, web development and app development with videos, quizzes and interactive coding exercises. Treehouse has beginner to advanced Python training that programmers of all levels benefit from. Tweet Read more about: Error Handling pythonforbeginners Nov. 12, 2013, 12:59 a.m. this will print the exception: except Exception, e: print str(e) or, more complete, with the name of the Exception and the value: except Exception, e: print repr(e)
Prachi Nov. 12, 2013, 12:44 a.m. Wht if i didn't know the excptwith exceptions. What is an Exception? An exception is an error that happens during execution of a program. When that error occurs, Python generate an exception that can be handled, which avoids your program to crash. Why use Exceptions? Exceptions are convenient in many ways for handling errors and special conditions in a program. When you think that you have a code which can produce an error then you can use exception handling. Raising an Exception You can raise an exception in your own program by using the raise exception statement. Raising an exception breaks current code execution and returns the exception back until it is handled. Exception Errors Below is some common exceptions errors in Python: IOError If the file cannot be opened. ImportError If python cannot find the module ValueError Raised when a built-in operation or function receives an argument that has the right type but an inappropriate value KeyboardInterrupt Raised when the user hits the interrupt key (normally Control-C or Delete) EOFError Raised when one of the built-in functions (input() or raw_input()) hits an end-of-file condition (EOF) without reading any data Exception Errors Examples Now, when we know what some of the exception errors means, let's see some examples: except IOError: print('An error occurred trying to read the file.') except ValueError: print('Non-numeric data found in the file.') except ImportError: print "NO module found" except EOFError: print('Why did you do an EOF on me?') except KeyboardInterrupt: print('You cancelled the operation.') except: print('An error occurred.') Try to use as few try blocks as possible and try to distinguish the failure conditions by the kinds of exceptions they throw. Set up exception handling blocks To use exception handling in Python, you first need to have a catch-all except clause. The words "try" and "except" are Python keywords and are used to catch exceptions. try-except [exception-name] (see above for examples) blocks The code within the try clause will be executed statement by statement. If an exception occurs, the rest of the try block will be skipped and the except clause will be executed. try: some statements here except: exception handling Let's see a short example on how to do this: try: print 1/0 except ZeroDivisionError: print "You can't divide by zero, you're silly." How does it work? The error handling is done through the use of exceptions that are caught in try blocks and handled in except blocks. If an error is encountered, a try block code execution is st