Python Exception Handling (Python Course)
- 1. Exception Handling Anton ( 王惇瑞） (F11157801)
- 3. INTRODUCTION Until now error messages haven’t been more than 2 type. There are (at least) two distinguishable kinds of errors: syntax errors and exceptions Source : https://docs.python.org/3/tutorial/errors.html#exceptions
- 4. SYNTAX ERROR The parser repeats the offending line and displays a little arrow pointing at the earliest point in the line where the error was detected. The error is caused by the token preceding the arrow. In the example the error is detected at the function print() since a colon (:) is missing ^ : indicate the part of error
- 5. EXCEPTION 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
- 6. EXCEPTION The last line of the error message indicates what happened, exception come in different types, and the type is printed as part of the message. For example ZeroDivisionError, NameError, and TypeError. The string printed as the exception type is the name of the built-in exception that occurred.
- 10. EXCEPTION HANDLING Illustration how exception handling works
- 11. EXCEPTION HANDLING It is possible to write programs that handle selected exceptions, like example in the above which asks the user for input until a valid integer has been entered, but allows the user to interrupt the program using “ctrl + c”
- 12. EXCEPTION HANDLING The try statement works as follows: 1. First, the try clause (the statement between try and except keywords) is executed 2. If no exception occurs, the except clause is skipped and execution of the try statement 3. If an exception occurs during execution of the try clause, the rest of the clause is skipped. Then if it’s type matches the exception named after the except keyword, the except clause is executed, then execution continues after the try/except block 4. If an exception occurs which does not match the exception named in the except clause, it is passed on to outer try statement; if no handler is found, it is an unhandled exception and execution stops
- 13. RAISING EXCEPTION The raise statement allows you to force an error to occur. We can define both the type of error and the text that prints to the user. That the argument to raise must either be an exception instance or a subclass deriving from an exception
- 14. RAISING EXCEPTION In the code block in the left, TypeError is the specified error. It has been set to occur anytime the variable x is not a string. The text inside the parentheses represents your chosen text to print to the user
- 15. Conclusion
- 16. Glosarium