Python-3.4.3/C3/Parsing-data/English-timed

Time	Narration
00:01	Welcome to the spoken tutorial on Parsing data.
00:06	In this tutorial, we will learn to- Split a string using a delimiter. Remove the leading, trailing and all whitespaces in a string and Convert between different built-in datatypes
00:22	To record this tutorial, I am using Ubuntu Linux 16.04 operating system Python 3.4.3 and IPython 5.1.0
00:38	To practice this tutorial, you should know how to use lists. If not, see the relevant Python tutorials on this website.
00:49	First, let us understand, what is meant by parsing data. Parsing the data is reading data in text form. It is converted into a form which can be used for computations.
01:04	Next we will learn about split() function.
01:08	split() function breaks up a larger string into smaller strings using a defined separator.
01:15	If no argument is specified, then whitespace is used as default separator.
01:22	Syntax is: str dot split inside parentheses argument
01:29	The split function parses a string and returns an array of tokens. This is called string tokenizing.
01:38	Let us first open the terminal by pressing Ctrl+Alt+T keys simultaneously.
01:46	Type ipython3 and press Enter.
01:52	Let us initialize the pylab package. Type percentage sign pylab and press Enter.
02:02	From here onwards, please remember to press the Enter key after typing every command on the terminal.
02:09	Let us define a variable str1 as string data type.
02:14	Type, str1 is equal to inside double quotes Welcome to insert some whitespaces, then Python tutorials
02:24	We can have any number of whitespaces between to and Python tutorials. But all the spaces are treated as one space.
02:34	Now, we are going to split this string on whitespace.
02:38	Type, str1 dot split open and close parentheses.
02:44	As we can see, we get a list of strings.
02:48	Let us take another example for split() function with argument. Type as shown.
02:57	Type, x dot split inside parentheses inside single quotes semicolon.
03:04	We get a list of strings separated by comma.
03:08	Pause the video. Try this exercise and then resume the video.
03:14	Split x using space as argument. Is it same as splitting without an argument?
03:22	Switch to the terminal for the solution.
03:26	Type b is equal to x dot split open and close parentheses.
03:32	Type c is equal to x dot split inside parentheses and inside single quotes space.
03:41	Type b
03:44	Type c
03:47	We can see that splitting without argument is same as giving space as argument.
03:54	Splitting the string without argument will split the string separated by any number of spaces.
04:01	And giving space as argument will split the sentence specifically on single whitespace.
04:08	Let us recall the variable str1.
04:12	Now, we will split this string without argument. Type b is equal to str1 dot split open and close parentheses.
04:24	Type c is equal to str1 dot split inside parentheses and inside single quotes space.
04:33	Type b
04:36	Type c
04:38	As you can see, here b is not equal to c since c has whitespaces as entries, whereas b has only words.
04:49	Next we will learn about strip method.
04:53	strip function removes all leading and trailing whitespaces in a string
04:59	Let us define a string by typing unstripped is equal to inside double quotes space Hello world space
05:09	Now to remove the whitespace, type, unstripped dot strip open and close parentheses.
05:18	We can see that strip removes all the whitespaces in the beginning and at the end of the string.
05:25	After splitting and stripping we get a list of strings with leading and trailing spaces stripped off.
05:32	Now we shall look at converting strings into floats and integers.
05:38	Type, mark underscore str is equal to inside double quotes 1.25
05:46	Note that 1.25 is a string and not a float as it is within double quotes.
05:53	Type, mark is equal to float inside parentheses mark underscore str. Here we are converting string to float.
06:05	Type type inside parentheses mark underscore str. This tells you the datatype of mark_str i.e. string.
06:17	Type type inside parentheses mark . This shows mark is a float datatype.
06:26	We can see that string is converted to float. Now we can perform mathematical operations on them.
06:34	Pause the video. Try this exercise and then resume the video.
06:40	What happens if you type, int inside parentheses inside double quotes 1.25 in the terminal?
06:48	Switch to the terminal for the solution.
06:52	Type, int inside parentheses inside double quotes 1.25
06:59	We can see a ValueError. We cannot convert a string to integer directly.
07:06	Let us see the correct solution for this. Type dcml underscore str is equal to inside double quotes 1.25.
07:18	Type flt is equal to float inside parentheses dcml underscore str.
07:27	Here we are converting the string into float as we cannot directly convert it into integer.
07:34	Type flt
07:37	Type, number is equal to int inside parentheses flt. We are now converting float into integer.
07:48	Type number We got the output as integer.
07:54	This is how we should convert strings into floats and integers.
07:59	Next, we will use a data file to parse the data.
08:04	Let me open the file student underscore record.txt in text editor.
08:10	The file student underscore record.txt is available in the Code files link of this tutorial. Please download it in your Home directory and use it.
08:22	We will first read the file line by line and parse each record in this file.
08:28	It contains records of students and their marks in the State Secondary Board Examination.
08:35	It has 1 lakh 80 thousand lines of record. We are going to read it and process this data.
08:43	Each line in the file is a set of fields separated by semicolons.
08:49	Consider a sample record from this file.
08:53	The following are the fields in any given line. Region Code Roll Number Name Marks of 5 subjects Total marks
09:08	Open a new text editor. Type the code as shown.
09:14	Let me explain this program.
09:17	We have already learnt for loop in earlier tutorial. The for loop will process the student record and split the fields of each record.
09:28	The math marks are then converted to float.
09:32	Then it is appended and stored as a list in a variable math underscore marks underscore A for region code A.
09:41	Save the file as marks.py in the Home directory.
09:48	Switch to the terminal.
09:51	Execute the file with percentage sign run space marks.py.
09:58	Switch back to the editor. Now we have all the math marks for region A in the list math underscore marks underscore A.
10:09	Add the below lines to calculate the mean of math marks for region A.
10:15	For this, we just have to sum the math marks and divide by the length.
10:21	Note that the length will give the number of students in region ‘A’.
10:26	Let us save the file.
10:29	Switch to the terminal.
10:32	Execute the file again with percentage sign run space marks.py.
10:40	Hence we got our final output.
10:43	Here the mean value for region A is calculated roughly for 1 lakh 80 thousand records.
10:51	This is how we split and read a huge data and perform computations on it.
10:57	This brings us to the end of this tutorial.
11:01	In this tutorial, we learnt to, Tokenize a string Split a string separated by delimiters with split() function
11:11	Remove whitespaces using the strip() function. Convert datatypes of numbers from one type to another Parse input data and perform computations on it.
11:25	Here are some self assessment questions for you to solve 1. How do you split the string “Guido;Rossum;Python" to get the words?
11:36	2. What does int inside paranthesis inside double quotes 20.0 produce?
11:43	And the answers - 1. line.split inside parantheses inside single quotes comma 2. int inside parantheses inside double quotes 20.0 will give an error, because converting a string directly into integer is not possible.
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12:16	Spoken Tutorial Project is funded by NMEICT, MHRD, Govt. of India. For more details, visit this website.
12:27	This is from IIT Bombay signing off. Thanks for watching.

Contributors and Content Editors

Pratik kamble