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

Time	Narration
00:00	Hello Friends and Welcome to the tutorial on "Getting started with files".
00:08	At the end of this tutorial, you will be able to, Open a file. Read the contents of the file line by line. Read the entire content of file at once. Append the lines of a file to a list. Close the file.
00:24	Before beginning this tutorial,we would suggest you to complete the tutorial on "Getting started with Lists" and "Getting started with For".
00:34	So now, open the terminal and start ipython
00:37	So type ipython space hyphen pylab.
00:46	Let us first open the file, pendulum dot txt present in slash home slash fossee slash .
00:54	So type f is equal to open within brackets and single quotes slash home slash fossee slash pendulum dot txt.
01:11	Here f is called a file object.
01:14	Let us type f on the terminal to see what it is.
01:17	So type f and hit Enter.
01:22	The file object shows the filepath and mode of the file which is open.
01:27	'r' stand for read only mode and 'w' stands for write mode.
01:32	As you can see, this file is open in read only mode.
01:40	We shall first learn to read the whole file into a single variable.
01:47	We use the read method to read all the contents of the file into the variable,pend.
01:53	So type pend is equal to f dot read closing brackets and hit Enter.
02:02	Now, let us see what pend contains, by typing Print space pend
02:11	We can see that pend has all the data of the file.
02:15	Type just pend to see more explicitly, what it contains.
02:25	So now, Pause the video here, try out the following exercise and resume the video.
02:30	Split the variable into a list, pend underscore list, of the lines in the file.
02:40	We use the function split lines to solve this problem.
02:44	So type pend underscore list is equal to pend dot split lines closing brackets and hit Enter.
03:05	Now, let us learn to read the file line-by-line.
03:11	But, before that we will have to close the file, since the file has already been read till the end.
03:19	Let us close the file opened into f.
03:24	Then type f dot close closing brackets and hit Enter.
03:29	Again type f on the prompt to see what it contains.
03:37	Notice, that it now says the file has been closed.
03:42	It is a good programming practice to close any file objects that we have opened, after their job is done.
03:50	Let us, now move on to reading files line-by-line.
03:54	Pause the video here, try out the following exercise and resume the video.
04:00	Re-open the file pendulum dot txt with f as the file object.
04:05	We just use the up arrow until we reach the open command and issue it again.Then hit Enter.
04:18	Now, to read the file line-by-line, we iterate over the file object line-by-line, using the for command.
04:27	Let us iterate over the file line-wise and print each of the lines.
04:35	So type in the command for space line space in space f colon , then , print line.
04:47	line is a variable, sometimes called the loop variable, and it is not a keyword.
04:53	We could have used any other variable name, but line seems meaningful enough.
05:00	Instead of just printing the lines, let us append them to a list, line underscore list .
05:07	We first initialize an empty list, line underscore list.
05:12	for that type line underscore list is equal to square bracket and hit Enter.
05:22	Let us then read the file line-by-line and then append each of the lines to the list.
05:30	We could, as usual close the file using f.close and re-open it.
05:36	But, this time, let's leave alone the file object f and directly open the file within the for statement.
05:43	This will save us the trouble of closing the file, each time we open it.
05:49	So type for line in open within brackets and single quotes slash home slash fossee slash pendulum dot txt colon line underscore list dot append within brackets line,Hit Enter.
06:22	Let us see what line underscore list contains.
06:26	so type line underscore list and hit Enter.
06:33	Notice that line_list is a list of the lines in the file, along with the newline characters.
06:42	If you noticed, pend underscore list did not contain the newline characters, because the string pend was split on the newline characters.
06:52	We can strip out the newline characters from the lines by using some string methods which we shall look in the further tutorial on strings.
07:04	So now, This brings us to the end of this tutorial. Lets revise what we have learnt,
07:12	Open and close files using the open and close functions respectively.
07:17	Read the data in the files as a whole,by using the read function.
07:22	Read the data in the files line by line by iterating over the file object using the for loop.
07:31	and finally Append the lines of a file to a list using the append function within the for loop.
07:38	Here are some self assessment questions for you
07:42	The open function returns a
07:46	string
07:48	list,file object
07:50	function
07:52	What does the function splitlines() do.
07:57	Displays the data as strings,all in a line
08:01	Displays the data line by line as strings
08:03	Displays the data line by line but not as strings
08:07	So now,let us look at the answers,
08:09	The function open , returns a file object.
08:15	The function splitlines displays the data line by line as strings.
08:21	So we hope you have enjoyed this tutorial and found it useful.
08:27	Thank you!

Contributors and Content Editors

Gaurav, Minal, PoojaMoolya, Sneha