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Hello.

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Welcome to the session on errors and exceptions.

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There are two types of arrows that typically occur when writing programs.

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Syntax errors and exceptions syntax errors occurred due to incorrect structure of the program.

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This means that the programmer has made a mistake in the structure of a statement or an expression even

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lousy.

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An example in the Jupiter note book.

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In this example here I have a print function that in an if statement and when we executed this line

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Python interpreter has thrown a syntax error.

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And if you notice in the output the line where the error was detected is displayed.

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And also we have a little arrow here pointing at the earliest point in the line where the error was

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detected.

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And if you notice carefully the colon that should follow after the next statement is missing and apart

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from the error messages and the line where the error was detected in the output the file name and a

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line number are printed so we know where to look.

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In case the input came from a script so we will put a call in after the if statement here and then execute

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this line.

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So there are no syntax errors in this line.

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All right next even if a statement or an expression is syntactically correct it may cause a Nader when

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an attempt is made to executed and errors that occur while executing a program are known as exceptions

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and we will see examples of different types of exceptions built in exceptions raised while executing

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our code.

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Both types of these errors these syntax errors and exceptions hide the execution of the program as soon

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as they're encountered.

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So now let's go and see some examples of exceptions next.

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In this example here I'm trying to divide the number two by zero and when we tried to execute this line

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the Python interpreter has thrown this exception and in the last line of the error message indicate

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what happened says Zito.

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Division error and the rest of the line provide details based on the type of the exception and what

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caused it.

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So.

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Division by zero is not allowed.

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So let's change this denominator.

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Say we will give 2 divided by 7 and then execute so here we have a floating point number.

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Now let's look at another example.

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Let us know divide the number 2 with debatable X and now the Python interpreter has raised an exception

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and this exception is name error and the last line of the error message displays what kind of exception

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is encountered.

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So name error is the exception and in the details we see that the name X or the variable x is not defined.

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So nowhere in our program we have defined the variable X and we have started using this variable in

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our operations and it is not allowed let's look at another example.

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We will not concatenate a string with a number and see if this is possible.

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And then execute.

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Now the Python interpreter has thrown an exception.

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The exception is a tight budget.

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That's because we are trying to concatenate a string but an integer which is not possible.

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Now let let's define a list list one contains the numbers 1 2 and 3.

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Now let's try accessing these elements in the list.

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List of 0 gives me the first element.

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Let's try to access element number four element add position 4.

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So as you can see there are only three elements that we have defined in the list.

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List 1.

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But when we are trying to access the elements in the list we have given the index number as for and

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there is no number.

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With this index in the list and hence the interpreter has raised this exception Index a list index out

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of range.

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Next we will try to import a script using the import statement and then execute this line and the interpreter

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has thrown this exception module not phone we have not created any module with this name test.

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So these are all the different errors that have occurred while executing the program and these errors

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are called exceptions.

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And when this happens we say Python has raised an exception or an exception is thrown whenever such

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errors or exceptions happen.

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Python creates a special type of object which contains all the relevant information about the error

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that has occurred.

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For example it contains the line number at which the edit occurred.

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The error messages and so on and by default the exceptions hard the execution of the program.

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The last line of the error message indicates what happened and the rest of the line provides details

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based on the type of exception and what caused it and the preceding part of the error message here shows

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the context where the exception happened in the form of a stack trace back.

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So when our program detects a fund that will keep it from completing as expected or will generate erroneous

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results we should hold for the execution and report the error by throwing an exception and bringing

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an exception to attention as call raising the exception and if the exception is left unattended the

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default behavior is for the interpreter to print a full trace back an error message included in the

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exception for some script.

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This behavior is sufficient but it is nice to catch the exception and print a more user friendly version

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of the error so we can decide how our programs respond to different types of errors.

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We may want to prompt the user for more input or display extended a road or a warning message.