PoojaMoolya: Created page with "{|- border=1 | '''Time''' | '''Narration''' |- | 00:01 | Hello Friends. Welcome to the tutorial on "Getting started with '''files'''". |-..."

2019-05-30T12:20:46Z

Created page with "{|- border=1 | <center>'''Time'''</center> | <center>'''Narration'''</center> |- | 00:01 | Hello Friends. Welcome to the tutorial on "Getting started with '''files'''". |-..."

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{|- border=1
| <center>'''Time'''</center>
| <center>'''Narration'''</center>

|-
| 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'''

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| 01:20
|w is for '''Write mode'''

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| 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.

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| 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'''

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| 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'''

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| 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.

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| 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'''.

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| 04:57
|Type '''f dot close ''' ''open and close parentheses''

Press '''Enter'''

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| 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'''.

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| 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.

|}

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

PoojaMoolya: Created page with "{|- border=1 | '''Time''' | '''Narration''' |- | 00:01 | Hello Friends. Welcome to the tutorial on "Getting started with '''files'''". |-..."