Difference between revisions of "Python-3.4.3/C2/Getting-started-with-files/English"

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Line 20: Line 20:
  
 
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| At the end of this tutorial, you will learn to -
 
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| At the end of this tutorial, you will learn to -
 
 
 
# Open a file.
 
# Open a file.
 
# Read the contents of the file line by line.
 
# Read the contents of the file line by line.
 
# Read the entire content of the file at once.
 
# Read the entire content of the file at once.
# Append the lines of a file to a list and
+
# Append the lines of a file to a '''list''' and
 
# Close the file.
 
# Close the file.
 
 
  
 
|-
 
|-
Line 39: Line 35:
 
* '''Python 3.4.3 '''and
 
* '''Python 3.4.3 '''and
 
* '''IPython 5.1.0'''<br/>  
 
* '''IPython 5.1.0'''<br/>  
 
 
 
  
 
|-
 
|-
Line 49: Line 42:
 
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| To practice this tutorial, you should know about
 
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| To practice this tutorial, you should know about
  
* Lists and
+
* '''Lists''' and
* '''for''' statement
+
* '''for statement'''
  
If not, see the pre-requisite Python tutorials on this website.
+
If not, see the pre-requisite '''Python''' tutorials on this website.
  
 
|-
 
|-
Line 70: Line 63:
 
Filename - name of the file to be opened.
 
Filename - name of the file to be opened.
  
Mode- indicates how the file is going to be opened.
+
Mode - indicates how the file is going to be opened.
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| To open a file for reading or writing, we can use a built in function called '''open()'''.
+
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| To open a file for reading or writing, we can use a '''built in function''' called '''open()'''.
  
  
'''Open() '''function returns a file object.
+
'''Open() function''' returns a '''file object'''.
  
  
The syntax is shown here:
+
The syntax is shown here.
  
  
'''Filename''' - is the name of the file to be opened.
 
  
'''Mode'''- This indicates how the file is going to be opened.
 
  
  
 +
'''Filename''' - is the name of the file to be opened.
  
 +
'''Mode'''- This indicates how the file is going to be opened.
  
 
|-
 
|-
Line 104: Line 97:
  
 
r+ - Read and Write
 
r+ - Read and Write
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| r- represent the Read mode
+
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| r- is for '''Read mode'''
  
w- is for Write mode  
+
w- is for '''Write mode'''
  
a - represents Appending mode and
+
a - represents '''Appending mode''' and
  
r+ - for both Read and Write mode
+
r+ - for both '''Read and Write mode'''
  
  
Specifying mode is optional.
+
Specifying '''mode''' is optional.
  
 
|-
 
|-
 
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| Open pendulum.txt in text editor  
 
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| Open pendulum.txt in text editor  
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| Let us open a file, '''pendulum.txt''' in a text editor.
+
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| Let us open a file '''pendulum.txt''' in a text editor.
  
 
|-
 
|-
 
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| Point to the columns in the file
 
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| Point to the columns in the file
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| This file contains 2 data columns, length and time of pendulum.
+
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| This file contains 2 data columns, '''length''' and '''time''' of '''pendulum'''.
  
  
 
We will be using this text file for our demonstration.
 
We will be using this text file for our demonstration.
 
 
 
  
 
|-
 
|-
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"|  
+
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| Text box on the screen as per the narration
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| The file '''pendulum.txt''' is available in the code file link of this tutorial.  
+
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| The file '''pendulum.txt''' is available in the '''Code File link''' of this tutorial.  
  
  
Please download it in '''Home''' directory and use it.
+
Please download it in '''Home directory''' and use it.
  
 
|-
 
|-
Line 141: Line 131:
 
Press '''Ctrl+Alt+T '''keys
 
Press '''Ctrl+Alt+T '''keys
  
Type
+
Type '''ipython3'''
 
+
'''ipython3'''
+
 
+
 
+
 
+
 
| style="background-color:#ffffff;border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.014cm;padding-right:0.191cm;"| Let us first open the '''Terminal '''by pressing '''Ctrl+Alt+T '''keys simultaneously.  
 
| style="background-color:#ffffff;border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.014cm;padding-right:0.191cm;"| Let us first open the '''Terminal '''by pressing '''Ctrl+Alt+T '''keys simultaneously.  
  
Line 158: Line 143:
  
 
'''%pylab '''and press '''Enter.'''
 
'''%pylab '''and press '''Enter.'''
| style="background-color:#ffffff;border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.014cm;padding-right:0.191cm;"| Let us initialise the '''pylab''' package.
+
| style="background-color:#ffffff;border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.014cm;padding-right:0.191cm;"| Let us initialise the '''pylab package'''.
  
  
 
Type '''%pylab '''and press''' Enter.'''
 
Type '''%pylab '''and press''' Enter.'''
  
Let us clear the terminal.
+
Let us clear the '''terminal'''.
  
 
|-
 
|-
| style="background-color:#ffffff;border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.014cm;padding-right:0.191cm;"|  
+
| style="background-color:#ffffff;border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.014cm;padding-right:0.191cm;"| Open pendulum.txt
| style="background-color:#ffffff;border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.014cm;padding-right:0.191cm;"| Let us open the file, '''pendulum.txt.'''
+
| style="background-color:#ffffff;border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.014cm;padding-right:0.191cm;"| Let us open the file '''pendulum.txt.'''
  
 
|-
 
|-
Line 173: Line 158:
  
  
Type
+
Type '''f = open('pendulum.txt')'''
 
+
'''f = open('pendulum.txt')'''
+
 
| style="background-color:#ffffff;border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.014cm;padding-right:0.191cm;"| Type  
 
| style="background-color:#ffffff;border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.014cm;padding-right:0.191cm;"| Type  
  
Line 182: Line 165:
  
  
Here the mode is not specified'''. '''
+
Here the '''mode''' is not specified.
  
By default, it is ‘r’.
+
By default, it is '''‘r’'''.
  
 
|-
 
|-
 
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| <nowiki>[IPython Terminal]</nowiki>
 
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| <nowiki>[IPython Terminal]</nowiki>
  
Type
+
Type '''f'''
 
+
'''f'''
+
 
+
 
+
  
 
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| Let us type '''f''' on the '''terminal''' to see what it is.
 
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| Let us type '''f''' on the '''terminal''' to see what it is.
  
  
The file object f, shows the filename and mode of the file, which is open.  
+
The '''file object f''' shows the filename and '''mode''' of the file which is open.  
  
 
|-
 
|-
Line 204: Line 183:
  
 
Highlight '''filename '''and '''mode 'r''''
 
Highlight '''filename '''and '''mode 'r''''
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| ''''r' '''stands for '''read''' only '''mode'''.
+
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| ''''r' '''stands for '''read only mode'''.
  
As you can see, this '''file''' is '''open''' in '''read''' only '''mode'''.
+
As you can see, this '''file''' is open in '''read only mode'''.
  
 
|-
 
|-
Line 213: Line 192:
  
  
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| Now let us learn to '''read''' the whole '''file''' into a single '''variable'''.  
+
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| Now let us learn to read the whole '''file''' into a single '''variable'''.  
  
 
|-
 
|-
Line 225: Line 204:
  
  
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| '''Type'''
+
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| Type
 
+
 
+
 
'''pend '''''equal to '''''f '''''dot '''''read'' '''open and close parentheses.''
 
'''pend '''''equal to '''''f '''''dot '''''read'' '''open and close parentheses.''
  
  
We use the '''read method''' to '''read''' all the contents of the file into the '''variable''', '''pend'''
+
We use the '''read method''' to read all the contents of the file into the '''variable pend'''
  
  
Line 237: Line 214:
  
  
To use read method we use the file object dot read method.
+
To use '''read method''' we use the '''file object dot read method'''.
  
 
|-
 
|-
Line 254: Line 231:
 
|-
 
|-
 
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| Point to the data
 
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| Point to the data
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| We can see that '''pend''' has all the '''data''' of the '''file pendulum.txt'''.
+
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| We can see that '''pend''' has all the data of the '''file pendulum.txt'''.
  
 
|-
 
|-
Line 265: Line 242:
  
  
We can see the newline characters as well in the output.
+
We can see the '''newline characters''' as well, in the output.
  
 
|-
 
|-
Line 272: Line 249:
  
  
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| Let us learn to split the variable '''pend''' into a list of lines in the file.
+
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| Let us learn to split the '''variable pend''' into a '''list''' of lines in the file.
  
  
We use the method '''splitlines''' to '''split''' a '''file''' of data into '''list''' of lines.
+
We use the '''method splitlines''' to split a file of data into '''list''' of lines.
  
 
|-
 
|-
Line 284: Line 261:
  
 
'''pend_list = pend.splitlines()'''
 
'''pend_list = pend.splitlines()'''
 
+
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| For this we need to store this '''list '''in a '''variable''', say '''pend_list'''
 
+
'''pend_list'''
+
 
+
 
+
Highlight the data into list of lines
+
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| For this we need to store this '''list '''in a variable, say '''pend_list'''
+
  
 
Type
 
Type
Line 298: Line 269:
 
Press '''Enter'''
 
Press '''Enter'''
  
 
+
|-
Type
+
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| Type '''pend_list'''
 
+
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"|
'''pend '''''underscore '''''list '''
+
Type '''pend '''''underscore '''''list '''
  
 
Press '''Enter'''
 
Press '''Enter'''
  
 
+
|-
We got the data into list of lines.
+
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"|Highlight the data into list of lines
 +
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| We got the data into '''list''' of lines.
  
 
|-
 
|-
 
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| Highlight the data into list of lines
 
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| Highlight the data into list of lines
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| '''pend_list''' does not contain '''newline''' '''characters '''like '''\n'''.
+
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| '''pend_list''' does not contain '''newline characters '''like '''\n'''.
  
  
This is because the string '''pend''' is '''split''' on the '''newline''' '''characters'''.  
+
This is because the '''string pend''' is split on the '''newline characters'''.  
  
 
|-
 
|-
 
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"|  
 
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"|  
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| Now, let us learn to read the file line-by-line.  
+
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"|  
 +
But, before that we will have to close the file, since the file has already been read till the end.
  
 
|-
 
|-
Line 324: Line 297:
  
 
'''f.close()'''
 
'''f.close()'''
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| But, before that we will have to close the file, since the file has already been read till the end.
+
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| Let us close the '''file''' opened into '''f'''.  
  
 +
Type '''f  dot close ''' ''open and close parentheses''
  
Let us close the '''file''' opened into f.
+
Press '''Enter'''
 
+
Type '''f '''''dot '''''close '''''open and close parentheses''
+
 
+
Press Enter
+
  
 
|-
 
|-
Line 341: Line 311:
  
  
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| It is a good programming practice to '''close''' any '''file''' '''objects''' that we have opened, after their job is done.
+
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| It is a good programming practice  
 
+
* to '''close''' any '''file objects''' that we have opened
|-
+
* after their job is done.
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"|
+
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| Let us, now move on to '''reading''' '''files''' '''line'''-'''by'''-'''line'''.  
+
  
 
|-
 
|-
Line 357: Line 325:
  
  
Re-open the file '''pendulum.txt''' with '''f''' as the file object.
+
Re-open the file '''pendulum.txt''' with '''f''' as the '''file object'''.
  
Recall, that we have closed the file earlier.
+
Recall that we have closed the file earlier.
 +
 
 +
Let us switch back to the terminal.
 +
 
 +
|-
 +
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"|
 +
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| Let us now move on to reading files line- by - line.  
  
 
|-
 
|-
Line 365: Line 339:
  
 
Type'''f = open('pendulum.txt')'''
 
Type'''f = open('pendulum.txt')'''
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| Let us switch back to the terminal.
+
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"|  
  
 
To re-open the file again, type  
 
To re-open the file again, type  
Line 380: Line 354:
 
'''print(line)'''
 
'''print(line)'''
  
 
+
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| Now, to read the file line-by-line, we '''iterate''' over the '''file object''' using the '''for loop'''.  
 
+
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| Now, to '''read''' the '''file''' line-by-line, we '''iterate''' over the '''file''' '''object''' line-by-line, using the '''for''' '''loop'''.  
+
  
  
Line 388: Line 360:
  
  
Let us clear the terminal.
+
Let us clear the '''terminal'''.
  
 
Type  
 
Type  
  
'''for line in f '''''colon ''press '''Enter'''
+
'''for line in f colon''' press '''Enter'''
  
''four spaces''''' print''''' inside parentheses '''''line'''
+
'''four spaces print inside parentheses line'''
  
 
|-
 
|-
Line 401: Line 373:
  
 
Highlight '''line'''
 
Highlight '''line'''
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| Here, '''line''' is a '''loop''' '''variable''', and it is not a keyword.  
+
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| Here, '''line''' is a '''loop variable''', and it is not a '''keyword'''.  
  
  
 
We could have used any other '''variable''' name, but '''line''' seems meaningful enough.
 
We could have used any other '''variable''' name, but '''line''' seems meaningful enough.
  
Press Enter twice.
+
Press '''Enter''' twice.
  
 
|-
 
|-
Line 413: Line 385:
  
 
Highlight '''line'''
 
Highlight '''line'''
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| Instead of just printing the lines, let us append them to a list, say '''line_list'''.  
+
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| Instead of just printing the lines, let us append them into a '''list''', say '''line_list'''.  
  
 
|-
 
|-
Line 426: Line 398:
 
Type,
 
Type,
  
line ''underscore ''list ''is'' ''equal to ''open and close square brackets.
+
'''line ''underscore ''list ''is'' ''equal to ''open and close square brackets.'''
 +
Press Enter
  
 
|-
 
|-
Line 445: Line 418:
  
  
for line in open ''inside parentheses inside quotes ''pendulum ''dot'' txt colon ''press enter''
+
'''for line in open ''inside parentheses inside quotes ''pendulum ''dot'' txt colon''' press '''Enter'''
  
''four space'' line'' underscore'' list ''dot ''append i''nside parentheses'' line
+
'''''four space'' line'' underscore'' list ''dot ''append i''nside parentheses'' line'''
  
Press Enter twice.
+
Press '''Enter''' twice.
  
  
Here, the '''for''' loop '''reads''' the file '''pendulum.txt '''line-by-line .
+
Here, the '''for loop '''reads the file '''pendulum.txt '''line-by-line.
  
  
The '''append''' method will add each of the line to the list, '''line_list.'''
+
The '''append method''' will add each of the line to the '''list, line_list.'''
  
 
|-
 
|-
 
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"|  
 
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"|  
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| We could, as usual '''close''' the file using '''f.close() '''and re-open it.  
+
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| We could, as usual close the file using '''f.close() '''and re-open it.  
  
 
|-
 
|-
 
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"|  
 
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"|  
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| But, this time, let's leave alone the '''file''' '''object''' '''f '''and directly open the file within the '''for''' '''statement'''.  
+
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| But, this time, let's leave the '''file object f '''and directly open the file within the '''for statement'''.  
  
  
Line 478: Line 451:
  
  
Type '''line '''''underscore '''''list '''and press '''Enter.'''
+
Type '''line ''underscore '' list '''and press '''Enter.'''
  
 
|-
 
|-
Line 485: Line 458:
  
 
Highlight '''newline characters'''
 
Highlight '''newline characters'''
 
+
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| '''line ''underscore '' list''' is a '''list''' of the lines in the file, along with the '''newline characters'''.  
 
+
 
+
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| If you noticed, '''line '''''underscore '''''list''' is a list of the lines in the file, along with the '''newline''' '''characters'''.  
+
  
 
|-
 
|-
 
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"|  
 
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"|  
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| We can '''strip''' out the '''newline''' '''characters''' from the lines by using some string methods.
+
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| We can strip out the '''newline characters''' from the lines by using some '''string methods'''.
  
This will be covered in the further tutorial on strings.
+
This will be covered in the further tutorial on '''strings'''.
  
 
|-
 
|-
Line 507: Line 477:
 
In this tutorial, we learnt to -
 
In this tutorial, we learnt to -
  
# Open and close files using the '''open''' and '''close''' methods respectively.
+
* Open and close files using the '''open''' and '''close methods''' respectively.
# Read the data in the files as a whole, by using the '''read''' method.
+
* Read the data in the files as a whole, by using the '''read method'''.
 
+
 
+
  
 
|-
 
|-
Line 518: Line 486:
 
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"|  
 
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"|  
  
# Read the data in the files line by line by iterating over the file object using the '''for loop'''.
+
* Read the data in the files line by line by iterating over the '''file object''' using the '''for loop'''.
# Append the lines of a file to a list using the '''append''' method within the '''for loop'''.
+
* Append the lines of a file to a '''list''' using the '''append method''' within the '''for loop'''.
 
+
 
+
  
 
|-
 
|-
Line 532: Line 498:
 
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| Here are some self assessment questions for you to solve
 
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| Here are some self assessment questions for you to solve
  
1. The '''open''' function returns a
+
1. The '''open function''' returns a
  
* string
+
* '''string'''
* list
+
* '''list'''
* file object
+
* '''file object'''
* function
+
* '''function'''
 
+
2. What does the function '''splitlines()''' do.
+
 
+
* Displays the '''data''' as '''strings''', all in a line
+
* Displays the '''data''' line by line as '''strings'''
+
* Displays the '''data''' line by line but not as '''strings'''
+
  
 +
2. What does the '''function splitlines()''' do.
  
 +
* Displays the data as '''strings''' all in a line
 +
* Displays the data line by line as '''strings'''
 +
* Displays the data line by line but not as '''strings'''
  
 
|-
 
|-
Line 554: Line 518:
 
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| And the answers are,
 
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| And the answers are,
  
# '''open '''function returns a '''file object'''
+
# '''open function''' returns a '''file object'''
# '''splitlines() '''displays the '''data''' line by line as '''strings'''
+
# '''splitlines() '''displays the data line by line as '''strings'''
 
+
 
+
  
 
|-
 
|-

Latest revision as of 12:09, 31 January 2018

Title of script: Getting started with files

Author: Trupti Kini

Keywords: IPython, files, read, write, append, mode, splitlines()

Visual Cue
Narration
Show Slide Hello Friends. Welcome to the tutorial on "Getting started with files".
Show Slide

Objectives


At the end of this tutorial, you will learn to -
  1. Open a file.
  2. Read the contents of the file line by line.
  3. Read the entire content of the file at once.
  4. Append the lines of a file to a list and
  5. Close the file.
Show slide

System Specifications

To record this tutorial, I am using
  • Ubuntu Linux 16.04 operating system
  • Python 3.4.3 and
  • IPython 5.1.0
Show Slide:

Pre-requisite

To practice this tutorial, you should know about
  • Lists and
  • for statement

If not, see the pre-requisite Python tutorials on this website.

Show slide

Open a file


Highlight according to narration: (open and file object)

syntax:


file_object = open(filename, mode)


Filename - name of the file to be opened.

Mode - indicates how the file is going to be opened.

To open a file for reading or writing, we can use a built in function called open().


Open() function returns a file object.


The syntax is shown here.



Filename - is the name of the file to be opened.

Mode- This indicates how the file is going to be opened.

Show slide

Open a file

syntax:


file_object = open(filename, mode)

r- Read mode

w- Write mode

a -Appending mode

r+ - Read and Write

r- is for Read mode

w- is for Write mode

a - represents Appending mode and

r+ - for both Read and Write mode


Specifying mode is optional.

Open pendulum.txt in text editor Let us open a file pendulum.txt in a text editor.
Point to the columns in the file This file contains 2 data columns, length and time of pendulum.


We will be using this text file for our demonstration.

Text box on the screen as per the narration The file pendulum.txt is available in the Code File link of this tutorial.


Please download it in Home directory and use it.

[Terminal]

Press Ctrl+Alt+T keys

Type ipython3

Let us first open the Terminal by pressing Ctrl+Alt+T keys simultaneously.


Type ipython3 and press Enter.

[IPython console]

Type

%pylab and press Enter.

Let us initialise the pylab package.


Type %pylab and press Enter.

Let us clear the terminal.

Open pendulum.txt Let us open the file pendulum.txt.
[IPython Terminal]


Type f = open('pendulum.txt')

Type


f is equal to open inside parentheses inside quotes pendulum dot txt


Here the mode is not specified.

By default, it is ‘r’.

[IPython Terminal]

Type f

Let us type f on the terminal to see what it is.


The file object f shows the filename and mode of the file which is open.

[IPython Terminal]

Highlight filename and mode 'r'

'r' stands for read only mode.

As you can see, this file is open in read only mode.

[IPython Terminal]


Now let us learn to read the whole file into a single variable.
Type

pend = f.read()


Highlight pend= f.read()


Type

pend equal to f dot read open and close parentheses.


We use the read method to read all the contents of the file into the variable pend


Press Enter


To use read method we use the file object dot read method.

[IPython Terminal]

Type

print(pend)

Now, let us see what pend contains, by typing

print inside parentheses pend.


Press Enter

Point to the data We can see that pend has all the data of the file pendulum.txt.
[IPython Terminal]

Type

pendHighlight data with newline characters

Type just pend to see more explicitly, what it contains.


We can see the newline characters as well, in the output.

[IPython Terminal]


Let us learn to split the variable pend into a list of lines in the file.


We use the method splitlines to split a file of data into list of lines.

[IPython Terminal]


Type

pend_list = pend.splitlines()

For this we need to store this list in a variable, say pend_list

Type

pend_list equal to pend dot splitlines open and close parentheses

Press Enter

Type pend_list

Type pend underscore list

Press Enter

Highlight the data into list of lines We got the data into list of lines.
Highlight the data into list of lines pend_list does not contain newline characters like \n.


This is because the string pend is split on the newline characters.

But, before that we will have to close the file, since the file has already been read till the end.

[IPython Terminal]


f.close()

Let us close the file opened into f.

Type f dot close open and close parentheses

Press Enter

[IPython Terminal]


Highlight closed file


It is a good programming practice
  • to close any file objects that we have opened
  • after their job is done.
Show Slide

Exercise 1


Pause the video here, try out the following exercise and then resume the video.


Re-open the file pendulum.txt with f as the file object.

Recall that we have closed the file earlier.

Let us switch back to the terminal.

Let us now move on to reading files line- by - line.
[IPython Terminal]

Typef = open('pendulum.txt')

To re-open the file again, type

f is equal to open inside parentheses inside quotes pendulum.txt

[IPython Terminal]

Type

for line in f:

print(line)

Now, to read the file line-by-line, we iterate over the file object using the for loop.


Let us iterate over the file line-wise and print each of the lines.


Let us clear the terminal.

Type

for line in f colon press Enter

four spaces print inside parentheses line

[IPython Terminal]


Highlight line

Here, line is a loop variable, and it is not a keyword.


We could have used any other variable name, but line seems meaningful enough.

Press Enter twice.

[IPython Terminal]


Highlight line

Instead of just printing the lines, let us append them into a list, say line_list.
[IPython Terminal]

Type

line_list = []

We first initialize a line_list as an empty-list


Type,

line underscore list is equal to open and close square brackets. Press Enter

[IPython Terminal]


Highlight according to narration.

Type

for line in open('pendulum.txt'):

line_list.append(line)


Type the code as


for line in open inside parentheses inside quotes pendulum dot txt colon press Enter

four space line underscore list dot append inside parentheses line

Press Enter twice.


Here, the for loop reads the file pendulum.txt line-by-line.


The append method will add each of the line to the list, line_list.

We could, as usual close the file using f.close() and re-open it.
But, this time, let's leave the file object f and directly open the file within the for statement.


This will save us the trouble of closing the file, each time we open it.

[IPython Terminal]


Type line_list and press Enter

Highlight data

Let us see what line_list contains.


Type line underscore list and press Enter.

[IPython Terminal]


Highlight newline characters

line underscore list is a list of the lines in the file, along with the newline characters.
We can strip out the newline characters from the lines by using some string methods.

This will be covered in the further tutorial on strings.

Show Slide

Summary


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.
  • Read the data in the files as a whole, by using the read method.
Show Slide

Summary

  • Read the data in the files line by line by iterating over the file object using the for loop.
  • Append the lines of a file to a list using the append method within the for loop.
Show Slide

Assignment


Here are some self assessment questions for you to solve

1. The open function returns a

  • string
  • list
  • file object
  • function

2. What does the function splitlines() do.

  • Displays the data as strings all in a line
  • Displays the data line by line as strings
  • Displays the data line by line but not as strings
Show Slide


Solutions

And the answers are,
  1. open function returns a file object
  2. splitlines() displays the data line by line as strings
Show Slide

Forum

Please post your timed queries in this forum.
Show Slide

Fossee Forum

Please post your general queries on Python in this forum.
Show Slide

Textbook Companion

FOSSEE team coordinates the TBC project.
Show Slide

Acknowledgment

http://spoken-tutorial.org

Spoken Tutorial Project is funded by NMEICT, MHRD, Govt. of India.

For more details, visit this website.

Previous slide This is Trupti Kini from IIT Bombay (or FOSSEE, if you wish) signing off.

Thank you.

Contributors and Content Editors

Nancyvarkey, Trupti