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

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Timing Narration
0:00 Hello Friends and Welcome to the tutorial on "Getting started with files".
0:08 At the end of this tutorial, you will be able to,
  1. Open a file.
  2. Read the contents of the file line by line.
  3. Read the entire content of file at once.
  4. Append the lines of a file to a list.
  5. Close the file.
0:24 Before beginning this tutorial,we would suggest you to complete the tutorial on "Getting started with Lists" and "Getting started with For".
0:34 So now, open the terminal and start ipython
0:37 So type ipython space hyphen pylab.
0:46 Let us first open the file, pendulum dot txt present in slash home slash fossee slash .
0:54 So type f is equal to open within brackets and single quotes slash home slash fossee slash pendulum dot txt.
1:11 Here f is called a file object.
1:14 Let us type f on the terminal to see what it is.
1:17 So type f and hit Enter.
1:22 The file object shows the filepath and mode of the file which is open.
1:27 'r' stand for read only mode and 'w' stands for write mode.
1:32 As you can see, this file is open in read only mode.
1:40 We shall first learn to read the whole file into a single variable.
1:47 We use the read method to read all the contents of the file into the variable,pend.
1:53 So type pend is equal to f dot read closing brackets and hit Enter.
2:02 Now, let us see what pend contains, by typing Print space pend
2:11 We can see that pend has all the data of the file.
2:15 Type just pend to see more explicitly, what it contains.
2:25 So now, Pause the video here, try out the following exercise and resume the video.
2:30 Split the variable into a list, pend underscore list, of the lines in the file.
2:40 We use the function split lines to solve this problem.
2:44 So type pend underscore list is equal to pend dot split lines closing brackets and hit Enter.
3:05 Now, let us learn to read the file line-by-line.
3:11 But, before that we will have to close the file, since the file has already been read till the end.
3:19 Let us close the file opened into f.
3:24 Then type f dot close closing brackets and hit Enter.
3:29 Again type f on the prompt to see what it contains.
3:37 Notice, that it now says the file has been closed.
3:42 It is a good programming practice to close any file objects that we have opened, after their job is done.
3:50 Let us, now move on to reading files line-by-line.
3:54 Pause the video here, try out the following exercise and resume the video.
4:00 Re-open the file pendulum dot txt with f as the file object.
4:05 We just use the up arrow until we reach the open command and issue it again.Then hit Enter.
4:18 Now, to read the file line-by-line, we iterate over the file object line-by-line, using the for command.
4:27 Let us iterate over the file line-wise and print each of the lines.
4:35 So type in the command for space line space in space f colon , then , print line.
4:47 line is a variable, sometimes called the loop variable, and it is not a keyword.
4:53 We could have used any other variable name, but line seems meaningful enough.
5:00 Instead of just printing the lines, let us append them to a list, line underscore list .


5:07 We first initialize an empty list, line underscore list.
5:12 for that type line underscore list is equal to square bracket and hit Enter.
5:22 Let us then read the file line-by-line and then append each of the lines to the list.
5:30 We could, as usual close the file using f.close and re-open it.
5:36 But, this time, let's leave alone the file object f and directly open the file within the for statement.
5:43 This will save us the trouble of closing the file, each time we open it.
5:49 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.


6:22 Let us see what line underscore list contains.
6:26 so type line underscore list and hit Enter.
6:33 Notice that line_list is a list of the lines in the file, along with the newline characters.
6:42 If you noticed, pend underscore list did not contain the newline characters, because the string pend was split on the newline characters.
6:52 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.
7:04 So now, This brings us to the end of this tutorial. Lets revise what we have learnt,
7:12 1. Open and close files using the open and close functions respectively.
7:17 2. Read the data in the files as a whole,by using the read function.
7:22 3. Read the data in the files line by line by iterating over the file object using the for loop.
7:31 and finally Append the lines of a file to a list using the append function within the for loop.
7:38 Here are some self assessment questions for you
7:42 1. The open function returns a
7:46 string
7:48 list
7:49 file object
7:50 function
7:52 2. What does the function splitlines() do.
7:57 Displays the data as strings,all in a line
8:01 Displays the data line by line as strings
8:03 Displays the data line by line but not as strings
8:07 So now,let us look at the answers,
8:09 1.The function open , returns a file object.
8:15 2. The function splitlines displays the data line by line as strings.


8:21 So we hope you have enjoyed this tutorial and found it useful.
8:27 Thank you!

Contributors and Content Editors

Gaurav, Minal, PoojaMoolya, Sneha