Python-3.4.3/C3/Getting-started-with-files/English-timed

Time	Narration
00:01	Hello Friends. Welcome to the tutorial on "Getting started with files".
00:07	At the end of this tutorial, you will learn to Open a file.
00:13	Read the contents of the file line by line.
00:16	Read the entire content of the file at once.
00:20	Append the lines of a file to a list and Close the file.
00:26	To record this tutorial, I am using Ubuntu Linux 16.04 operating system Python 3.4.3 and IPython 5.1.0
00:40	To practice this tutorial, you should know about Lists and for statement
00:48	If not, see the pre-requisite Python tutorials on this website.
00:54	To open a file for reading or writing, we can use a built in function called open().
01:01	Open() function returns a file object. The syntax is shown here. Filename is the name of the file to be opened.
01:12	Mode- This indicates how the file is going to be opened.
01:17	r is for Read mode
01:20	w is for Write mode
01:23	a represents Appending mode and r+ for both Read and Write mode Specifying mode is optional.
01:32	Let us open a file pendulum.txt in a text editor.
01:38	This file contains 2 data columns, length and time of pendulum. We will be using this text file for our demonstration.
01:49	The file pendulum.txt is available in the Code File link of this tutorial. Please download it in Home directory and use it.
02:00	Let us first open the Terminal by pressing Ctrl+Alt+T keys simultaneously.
02:07	Type ipython3 and press Enter.
02:12	Let us initialise the pylab package. Type %pylab and press Enter.
02:20	Let us clear the terminal.
02:23	Let us open the file pendulum.txt.
02:27	Type f is equal to open inside parentheses inside quotes pendulum dot txt
02:38	Here the mode is not specified. By default, it is ‘r’.
02:43	Let us type f on the terminal to see what it is.
02:48	The file object f shows the filename and mode of the file which is open.
02:57	'r' stands for read only mode. As you can see, this file is open in read only mode.
03:06	Now let us learn to read the whole file into a single variable.
03:11	Type pend equal to f dot read open and close parentheses.
03:18	We use the read method to read all the contents of the file into the variable pend Press Enter
03:27	To use read method we use the file object dot read method.
03:34	Now, let us see what pend contains, by typing print inside parentheses pend. Press Enter
03:44	We can see that pend has all the data of the file pendulum.txt.
03:50	Type just pend to see more explicitly, what it contains.
03:56	We can see the newline characters as well, in the output.
04:01	Let us learn to split the variable pend into a list of lines in the file.
04:07	We use the method splitlines to split a file of data into list of lines.
04:14	For this we need to store this list in a variable, say pend_list
04:21	Type pend_list equal to pend dot splitlines open and close parentheses Press Enter
04:33	Type pend underscore list Press Enter
04:37	We got the data into list of lines.
04:41	pend_list does not contain newline characters like \n.
04:47	This is because the string pend is split on the newline characters.
04:53	Let us close the file opened into f.
04:57	Type f dot close open and close parentheses Press Enter
05:04	It is a good programming practice to close any file objects that we have opened after their job is done.
05:11	Pause the video here, try out the following exercise and then resume the video.
05:17	Re-open the file pendulum.txt with f as the file object.
05:23	Recall that we have closed the file earlier.
05:27	Let us switch back to the terminal.
05:30	Let us now move on to reading files line by line.
05:34	To re-open the file again, type f is equal to open inside parentheses inside quotes pendulum.txt
05:47	Now, to read the file line-by-line, we iterate over the file object using the for loop.
05:54	Let us iterate over the file line-wise and print each of the lines. Let us clear the terminal.
06:03	Type for line in f colon press Enter four spaces print inside parentheses line
06:16	Here, line is a loop variable, and it is not a keyword.
06:21	We could have used any other variable name, but line seems meaningful enough. Press Enter twice.
06:30	Instead of just printing the lines, let us append them into a list, say line_list.
06:37	We first initialize a line_list as an empty-list
06:42	Type, line underscore list is equal to open and close square brackets. Press Enter
06:54	Type the code as for line in open inside parentheses inside quotes pendulum dot txt colon press Enter
07:10	four space line underscore list dot append inside parentheses line Press Enter twice.
07:23	Here, the for loop reads the file pendulum.txt line-by-line.
07:29	The append method will add each of the line to the list, line_list.
07:35	We could, as usual close the file using f.close() and re-open it.
07:42	But, this time, let's leave the file object f and directly open the file within the for statement.
07:50	This will save us the trouble of closing the file, each time we open it.
07:55	Let us see what line_list contains. Type line underscore list and press Enter.
08:05	line underscore list is a list of the lines in the file, along with the newline characters.
08:13	We can strip out the newline characters from the lines by using some string methods.
08:20	This will be covered in the further tutorial on strings.
08:25	This brings us to the end of this tutorial. In this tutorial, we learnt to - Open and close files using the open and close methods respectively.
08:38	Read the data in the files as a whole, by using the read method.
08:43	Read the data in the files line by line by iterating over the file object using the for loop.
08:50	Append the lines of a file to a list using the append method within the for loop.
08:56	Here are some self assessment questions for you to solve
09:01	1. The open function returns a string, list, file object, function
09:07	2. What does the function splitlines() do.
09:11	Displays the data as strings all in a line
09:14	Displays the data line by line as strings
09:18	Displays the data line by line but not as strings
09:24	And the answers are, 1. open function returns a file object
09:31	splitlines() displays the data line by line as strings
09:37	Please post your timed queries in this forum.
09:41	Please post your general queries on Python in this forum.
09:46	FOSSEE team coordinates the TBC project.
09:50	Spoken Tutorial Project is funded by NMEICT, MHRD, Govt. of India. For more details, visit this website.
10:01	Thats it for the tutorial. This is Trupti Kini from IIT Bombay (or FOSSEE, if you wish) signing off. Thank you.

Contributors and Content Editors

PoojaMoolya