Python-3.4.3/C4/Handling-Errors-and-Exceptions/English-timed

Time	Narration
00:01	Welcome to the spoken tutorial on Handling errors and exceptions.
00:07	In this tutorial, you will learn to, Understand errors and exceptions
00:14	Handle errors and exceptions
00:17	To record this tutorial, I am using Ubuntu Linux 16.04 operating system
00:25	Python 3.4.3 and IPython 5.1.0
00:32	To practise this tutorial, you should know how to use functions and carry-out testing and debugging.
00:43	If not, see the relevant Python tutorials on this website.
00:48	In Python there are two kinds of errors: syntax errors and exceptions
00:57	Syntax errors are caused by incorrect usages and these are detected by parser.
01:04	For example: if True print inside brackets inside double quotes done
01:11	It will give Syntax Error since colon is missing after True.
01:17	Exception is an error that occurs during execution of a program.
01:23	Python generates an exception that can be handled, which avoids the program to crash.
01:30	For example: 1/0 It will give ZeroDivisionError exception.
01:37	Let us see these examples in action. Open the terminal.
01:43	Type ipython3 and press Enter.
01:48	From here onwards remember to press the Enter key after typing every command on the terminal.
01:55	Now type if True print inside brackets inside double quotes done.
02:03	The output shows SyntaxError.
02:06	It displays an ‘arrow’ pointing at the earliest point in the line where the error was detected.
02:13	In our case, the error is caused by missing colon after True in If clause
02:20	Now type, 1 / 0 Python throws an exception called ZeroDivisionError.
02:29	Even though the expression is syntactically correct, we cannot divide a number by zero.
02:36	Exception is a special kind of failure reported by the programming language.
02:42	Let us see how can be deal with the Exceptions that occured in Programs
02:48	Type a = input inside brackets inside double quotes Enter an integer
02:57	I will enter ac as input. Now type, num is equal to int inside brackets a
03:07	When you run this code, it throws a 'ValueError' Exception. This is because, we are trying to convert the string to integer.
03:17	So now we can 'catch exceptions and write code to handle it. For this we have try and except clause in Python.
03:27	Here is the syntax of try....except...else blocks. First, the statements between the try and except keywords is executed.
03:38	If the statements do not cause any exception, the except clause is skipped.
03:44	If the statements cause any exception, then except clause is executed if exception name matches.
03:52	And the execution continues after the try statement
03:57	The code in the else-block executes if the code in the try: block does not raise an exception.
04:05	Type as shown. Give ac as input.
04:12	Now we will type the try and except blocks.
04:16	Press Enter twice to get the output.
04:20	In the previous example, We encountered a problem because we tried to convert the string ‘ac’ to integer.
04:28	Here conversion of string value to an integer is given inside try block.
04:34	ValueError exception is raised and so the output is displayed as Wrong input.
04:41	In the previous example, we found out what caused the error and then resolved to get a solution for it. This whole process is called debugging.
04:53	Next we will see another case in try except statement with else clause.
04:59	Lets change our previous code slightly. Type as shown. I will give input as 23.
05:10	Now type as shown. This try… except statement has an optional else clause.
05:20	It is useful if the try clause does not raise an exception.
05:25	Lets see another example for debugging. Create a file mymodule.py with the following code.
05:34	The variable ‘i’ is iterated from 0 to 9.
05:39	Let us run this code in Ipython. Type, from mymodule import test test open and close brackets
05:52	Interpreter gives us ZeroDivisionError because there is a division by zero error.
05:59	To find the value which caused the error, type Percentage debug
06:06	The code which caused the error is shown by an arrow.
06:11	The prompt has changed to ipdb which is the ipython debugger mode.
06:18	Using this debugger here, you can access variables in the previous code block.
06:24	We can check values of variables to inspect what went wrong.
06:29	For example, on typing ‘i’, we get 5 as output.
06:36	This means that the error was caused when the value of i became 5.
06:42	To exit from the ipdb prompt, press q and press Enter.
06:48	This brings us to the end of this tutorial. Let us summarize.
06:54	In this tutorial, we have learnt about Errors and exceptions.
07:00	Handling exception using try and except. Using percentage debug for debugging in ipython.
07:09	Here is a self assessment question for you to solve How do you start the debugger on ipython?
07:17	And the answer, We start the debugger on ipython by saying, percentage debug
07:25	Please post your timed queries in this forum.
07:29	Please post your general queries on Python in this forum.
07:34	FOSSEE team coordinates the TBC project.
07:38	Spoken Tutorial Project is funded by NMEICT, MHRD, Govt. of India. For more details, visit this website.
07:49	This is Priya from IIT Bombay signing off. Thank you.

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PoojaMoolya