TypeError: Argument should be an integer or a float value raise TypeError('Argument should be an integer or a float value') if type(n1) not in types_allowed or type(n2) not in types_allowed: raise by itself re-raises the currently active exception, if any ( RuntimeError otherwise). And you can optionally specify an error message.
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It accepts an optional error type, which can be either a built-in or a user defined one (see docs.python: User-defined Exceptions). You can also manually raise exceptions if needed. Here's a sample run: $ python3.9 try_except_else.py Num = int(input('Enter an integer number: '))
TRY EXCEPT PYTHON CODE
The use of the else clause is better than adding additional code to the try clause because it avoids accidentally catching an exception that wasn’t raised by the code being protected by the try. This block should be defined after the except block(s). If there's no exception raised in the try block, then the code in the else block will be executed. The else clause behaves similarly to the else clause seen with loops. See awesome-python: code-analysis for more such tools. There are static code analysis tools like pylint, "which looks for programming errors, helps enforcing a coding standard, sniffs for code smells and offers simple refactoring suggestions". See stackoverflow: avoid bare exceptions for details. It is not recommended to use except without passing an error type. See docs.python: built-in exceptions for documentation on built-in exceptions. Oops something went wrong! the error msg is: print(f'oops something went wrong! the error msg is:\n""') You can also capture the error message using the as keyword (which you have seen previously with import statement, and will come up again in later chapters). Here's a sample run: $ python3.9 try_except.py If you wish to take the same alternate path for multiple errors, you can pass a tuple to except instead of a single error type. It so happens that both int() and factorial() generate ValueError in the above example. Print('Not a positive integer, try again') Num = int(input('Enter a positive integer: ')) Here's an example to get a positive integer number from the user, and continue doing so if the input was invalid. Put the code likely to generate an exception inside try block and provide alternate path(s) inside one or more except blocks. In some cases, you want the program to end, but display a user friendly message instead of developer friendly traceback. For example, you could allow the user to correct their input data. You could implement alternatives to be followed for certain types of errors instead of premature end to the program execution. This may differ for user defined error types. You also get an error type, such as ValueError and ZeroDivisionError seen in the above example, followed by a message.
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When an exception occurs, the program stops executing and displays the line that caused the error. ZeroDivisionError: float division by zero ValueError: invalid literal for int() with base 10: '42x' Such errors are typically difficult or impossible to determine just by looking at the code. For example, passing a wrong data type to a function, dividing a number by 0 and so on. Synta圎rror: leading zeros in decimal integer literals are not permitted Įxceptions happen when something goes wrong during the code execution. Can you spot the rest of the syntax issues in the above program? $ python3.9 syntax_error.pyįile "/home/learnbyexample/Python/programs/syntax_error.py", line 5 Note that the syntax check happens before any code is executed, which is why you don't see the output for the print('hello') statement. The above code is using an unsupported syntax for a numerical value. Here's an example program with syntax errors: # syntax_error.py There are (at least) two distinguishable kinds of errors: syntax errors and exceptions Quoting from docs.python: Errors and Exceptions:
TRY EXCEPT PYTHON HOW TO
You'll also see how to raise exceptions programmatically. This chapter will discuss different types of errors and how to handle some of the them within the program gracefully.