Python/C3/Parsing-data/English-timed

Time	Narration
00:00	Hello friends and welcome to the tutorial on "Parsing Data".
00:06	At the end of this tutorial, you will be able to, Split a string using a delimiter. Remove the whitespace around the string. Convert the datatypes of variables from one type to other.
00:18	Before beginning this tutorial,we would suggest you to complete the tutorial on "Getting started with Lists".
00:23	Now, invoke the ipython interpreter by typing ipython on your terminal.
00:32	As you can see, each record consists of fields separated by a colon in the file sslc.txt.
00:51	The first record is region code, then roll number,name, marks of second language,first language, maths, science and social and total marks.
01:06	Our job is to calculate the arithmetic mean of all the maths marks in the region "B".
01:14	Now let us understand, what is meant by 'parsing data'.
01:19	From the input file, we can see that the data we have is in the form of text.
01:25	Parsing this data is all about reading it and converting it into a form which can be used for computations -- in our case,it will be a sequence of numbers.
01:40	We can clearly see that the problem involves reading files and tokenizing.
01:45	Let us learn about tokenizing strings.
01:48	We shall define a string first. Type line = within double quotes "parse this (a long space) string"
02:05	We are now going to split this string on white space. type line.split()
02:17	As you can see, we get a list of strings, which means, when split is called without any arguments, it splits on whitespace.
02:24	In simple words, all the spaces are treated as one big space.
02:29	The function split can also split on a string of our choice.
02:34	This is achieved by passing that as an argument.
02:36	But first lets define a sample record from the file.record = "A;015163;JOSEPH RAJ S;083;042;47;0;72;244" now type record.split within bracket in single quotes (';')
03:12	We can see that the string is split on the semi-colon and we get each field separately.
03:18	We can also observe that an empty string appears in the list since there are two semi colons without anything in between.
03:25	In short, split splits on white space if called without an argument and splits on the given argument if it is called with an argument.
03:33	Pause the video here, try out the following exercise and resume the video
03:39	Split the variable line using a space as argument.
03:43	Is it same as splitting without an argument ?Type on terminal record.split()
03:57	We see that when we split on space, multiple whitespaces are not clubbed as one and there is an empty string every time there are two consecutive spaces.
04:09	Now that we know how to split a string, we can split the record and retrieve each field separately.
04:16	But there is one problem,The region code "B" and a "B" surrounded by whitespace are treated as two different regions.
04:23	Hence, we must find a way to remove all the whitespace around a string so that the region code "B" and a "B" with white spaces are dealt as same.
04:32	This is possible by using the strip method of strings.
04:36	Let us define a string by typing unstripped = within double quotes a long space B again a long space unstripped.strip()
05:01	We can see that strip removes all the white space around the sentence.
05:07	Pause the video here, try out the following exercise and resume the video
05:13	What happens to the white space inside the sentence when it is stripped
05:19	We see that, the whitespace inside the sentence is only removed and the rest remains unaffected.
05:54	type a_str = " (a long space) white (again long space) space (and long space)"a_str.strip()By now we know enough to separate fields from the record and to strip out any white space.
06:06	The only road block we now have, is conversion of string to float.
06:12	The splitting and stripping operations are done on a string and their result is also a string.
06:17	Hence the marks that we have, are still strings and mathematical operations are not possible on them.
06:21	We must convert them into numbers (integers or floats), before we can perform mathematical operations on them.
06:31	So, We shall now look at converting strings into floats.
06:33	We define a float string first.
06:36	So Type mark_str = "1.25" mark = int(float(mark_str)) type within bracket(mark_str) type within bracket(mark)
07:22	We can see that string is converted to float.
07:26	We can perform mathematical operations on them now.
07:29	Pause the video here, try out the following exercise and resume the video
07:39	What happens if you do int within brackets "1.25"
07:46	So type int within brackets 1.25 in the terminal; it raises an error that converting an integer to float directly is not possible
08:00	It involves an intermediate type of conversion to float; hence you have to follow the following type of conversion
08:08	So type dcml underscore str is equal to within double quotes 1.25; then flt = float within brackets dcml underscore str ; then type flt
08:45	Then number is equal to int within brackets flt; then type number.
09:00	Using int, it is also possible to convert float into integers.
09:05	Now that we have all the machinery required to parse the file, let us solve the problem.
09:10	We first read the file line by line and parse each record.
09:14	We then see if the region code is B and store the marks accordingly.
09:26	So type math underscore marks underscore B is equalto empty brackets for line in open within brackets and double quotes slash home slash fossee slash sslc dot txt colon fields is equal to line dot split within brackets in double quotes colon; region underscore code is equal to fields within square brackets 0.region underscore code underscore stripped is equal to region underscore code dot strip and empty brackets.math underscore mark underscore str is equalto fields within square brackets 5 math underscore mark = float within brackets math underscore mark underscore str if region underscore code double equalto "B" colon math underscore marks underscore B dot append within brackets math underscore mark and hit enter
12:37	Now we have all the math marks of region "B" in the list math_marks_B.
12:45	To get the mean, we just have to sum the marks and divide by the length.type math_marks_mean = sum within brackets (math_marks_B)divided by that is slash / len within brackets(math_marks_B)math_marks_mean
13:24	Hence we get our final output.
13:27	This is how we split and read such a huge data and perform computations on it.
13:32	So, this brings us to the end of the tutorial.
13:37	In this tutorial, we have learnt to,1. Tokenize a string using various delimiters like semi-colons.
13:44	2. Split a data separated by delimiters by using the function split().
13:50	3. Get rid of extra white spaces around using the strip() function.
13:55	Convert data types of numbers from one type to another.
13:59	Parse input data and perform computations on it.
14:05	Here are some self assessment questions for you to solve
14:12	1. How do you split the string within double quotes "Guido;Rossum;Python" to get the words.
14:26	2. How will you remove the extra whitespace in this sentence " Hello World "
14:34	3. What does int within brackets in double quotes ("20.0") produce and the options are
14:40	20
14:42	20.0, Error
14:44	within double quotes "20"
14:47	And just look at the answers,
14:50	1. We can split the string the semi-colons by passing it as an argument to the split function as line.split within brackets(';')
15:03	" Hello World ".strip() will remove the extra whitespaces around the string.
15:11	and the last one int("20.0") will give an error, because converting a float string, 20.0, directly into integer is not possible.
15:25	Hope you have enjoyed this tutorial and found it useful.
15:28	Thank you.

Contributors and Content Editors

Gaurav, Minal, PoojaMoolya, Ranjana, Sneha