Python-3.4.3/C3/Getting-started-with-files/English-timed
From Script | Spoken-Tutorial
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| 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. |
