Error Handling Python
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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
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parsing errors, are perhaps the most common kind of complaint you get error handling c++ while you are still learning Python: >>> while True print('Hello world') File "
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by (or at least detected at) the token preceding the arrow: in the example, the error is detected at the function 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,
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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 "
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how to handle those. Exception handling allows us to continue our program (or terminate it) http://www.pythonforbeginners.com/error-handling/python-try-and-except if an exception occurs. Error Handling Error handling in Python is http://www.python-course.eu/exception_handling.php done through the use of exceptions that are caught in try blocks and handled in except blocks. Try and Except If an error is encountered, a try block code execution is stopped and transferred down to the except block. In addition to using an except error handling 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 an exception in your own program by using the raise exception [, value] statement. Raising an exception breaks current code execution and error handling python 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 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
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