Python programs for file handling Pract 7

File handling in python is vital with automation perspective.Files can be handled in python using many file operations,file modes,file methods and file attributes.

1. Write a Python program to read an entire text file.

2. Write a Python program to append text to a file and display the text.

3. Write a Python program to read last n lines of a file.

4. Write a Python program to show difference between ‘w’ mode and ‘a’ mode of file.

5. Write a Python program to calculate length of each line in file.

6. Write a Python program to read lines by applying loop on file object

7. Write a Python program to print specified characters from a file.

8. Write a Python program to print lines with ‘*’.

9. Write a Python program to show use of read(), readline() and readlines().

10. Write a Python program to show use of write(), writelines() and multiple write().

11. Write a Python program to determine file position using tell().

12. Write a Python program to get file position using seek().

Practical 6a : Write a Python program to read an entire text file.

"""
Author : ITVoyagers (https://itvoyagers.in)

Date :12th August 2019

Description :  Write a Python program to read an entire text file.
"""
def file_read(filename):
        #open() is used to open a file and to create a file object
        #txt is file object
        txt = open(filename)  
        print(txt.read()) #read() is used to read entire data in file 
file_read('itvoyagers.txt') #text file must be created priorly

OUTPUT

 >>> 

There are two types of files :
i) Text Files
ii) Binary Files

Text Files:
A text file is a structure containing sequence of lines and a line containing sequence of characters.A line is terminated by EOL (End OF Line) character.This type of file can hold alphabets, digits and symbols.
Commonly used extensions : database(csv,..),source files(c,py,cpp,..), etc
Binary files:
Binary files can be any sequence of bytes and must be opened in an appropriate program that knows the specific file format.
Commonly used extensions : images(jpg,gif,..), database(mdb,sqlite,..), executable(exe,dll,..) etc

To know more about file handling visit:

File Systems and File Handling in Python

NOTE : To get above output you must first create a text file named as itvoyagers.txt and write data into it

Practical 6b : Write a Python program to append text to a file and display the text.

"""
Author : ITVoyagers (https://itvoyagers.in)

Date :12th August 2019

Description : Write a Python program to append text to a file and display the text.
"""
#'a' mode can create a file if it does not exist
f=open('abc.txt','a')
#write() is used to write text into file in both 'a' and 'w' modes
f.write("easy to learnn")
f=open('abc.txt','r')
container=f.read()
print(container)
f.close()

OUTPUT

 >>> 

>>> 
easy to learn
easy to learn
easy to learn
easy to learn

NOTE : Program is executed 4 times to get above output

Practical 6c : Write a Python program to read last n lines of a file.

"""
Author : ITVoyagers (https://itvoyagers.in)

Date :12th August 2019

Description : Write a Python program to read last n lines of a file.
"""
f=open('itvoyagers.txt','r')
#readlines() is used to read entire file and returns list of lines
list_of_lines=f.readlines() 
n=int(input("enter number of of lines"))
print(list_of_lines[-n])
f.close() #close() performs clean up activities

OUTPUT

 >>> 
enter number of of lines 8
Commonly used extensions : database(csv,..),source files(c,py,cpp,..), etc

>>> ================================ RESTART ================================
>>> 
enter number of of lines 6
Binary files can be any sequence of bytes and must be opened in an appropriate program that knows the specific file format.

NOTE : itvoyagers.txt is already created in advance before using in this code

Practical 6d : Write a Python program to show difference between ‘w’ mode and ‘a’ mode of file.

"""
Author : ITVoyagers (https://itvoyagers.in)

Date :12th August 2019

Description : Write a Python program to show difference between 'w' mode and 'a' mode of file.
"""
#difference between 'w' and 'a'
""" 'w' mode is used to write in the file
by overwriting existing content"""

a=open("trial.txt","w")
a.write("itv n")
a.write("itv2 n")

a=open("trial.txt","r")
print(a.read())

""" 'a' mode is used to write in the file
by adding content at the end without overwriting"""

a=open("trial.txt","a")
a.write("itv3 n")

a=open("trial.txt","r")
print(a.read())

OUTPUT

 >>> 
itv 
itv2 

itv 
itv2 
itv3 

NOTE : Above program explains difference between append and write mode

Practical 6e : Write a Python program to calculate length of each line in file.

"""
Author : ITVoyagers (https://itvoyagers.in)

Date :12th August 2019

Description : Write a Python program to calculate length of each line in file.
"""
#prog to find length of each line of a file
f=open("abc.txt","r")
text=f.readlines()
print(text)
for line in text:
    print(len(line))

OUTPUT

 
>>> 
['easy to learnn', 'easy to learnn', 'easy to learnn', 'easy to learnn']
14
14
14
14


NOTE : As readlines() returns list of lines from file we can apply for loop on list and calculate length of each value.

Practical 6f : Write a Python program to read lines by applying loop on file object.

"""
Author : ITVoyagers (https://itvoyagers.in)

Date :12th August 2019

Description : Write a Python program to read lines by applying loop on file object
"""
f=open("abc.txt","r")
for line in f:
    print(line,end="")

OUTPUT

 
>>> 
easy to learn
easy to learn
easy to learn
easy to learn

NOTE : file object holds entire file ,so we can apply loops on it to retrieve data

Practical 6g : Write a Python program to print specified characters from a file.

"""
Author : ITVoyagers (https://itvoyagers.in)

Date :12th August 2019

Description : Write a Python program to print specified characters from a file.
"""
with open("abc.txt","r") as f:
    c=f.read(11)
    print(c)

OUTPUT

 
>>> 
easy to lea
>>> 

NOTE : We can provide n to read(n) to give number of characters to read.

Practical 6h : Write a Python program to print lines with ‘*’.

"""
Author : ITVoyagers (https://itvoyagers.in)

Date :12th August 2019

Description : Write a Python program to print lines with '*'.
"""
with open("abc.txt","r") as g:
    s=1
    c=g.read(s)
    while len(c)>0:
        print(c,end="*")
        c=g.read(s)

OUTPUT

 
>>> 
e*a*s*y* *t*o* *l*e*a*r*n*
*e*a*s*y* *t*o* *l*e*a*r*n*
*e*a*s*y* *t*o* *l*e*a*r*n*
*e*a*s*y* *t*o* *l*e*a*r*n*
*

NOTE : Here we are seeing a different syntax to create file object and also the use of “end”

Practical 6i : Write a Python program to show use of read(), readline() and readlines().

"""
Author : ITVoyagers (https://itvoyagers.in)

Date :12th August 2019

Description : Write a Python program to show use of read(), readline() and  readlines().
"""
with open("abc.txt",'r') as f:
    c=f.read()
    print("OUTPUT OF read()")
    print(c)

with open ("abc.txt") as f:
    c=f.readline()
    print("OUTPUT OF readline()")
    print(c)

with open ("abc.txt") as f:
    c=f.readlines()
    print("OUTPUT OF readlines()")
    print(c)

OUTPUT

 
>>> 
OUTPUT OF read()
easy to learn
easy to learn
easy to learn
easy to learn

OUTPUT OF readline()
easy to learn

OUTPUT OF readlines()
['easy to learnn', 'easy to learnn', 'easy to learnn', 'easy to learnn']

Practical 6j : Write a Python program to show use of write(), writelines() and multiple write().

"""
Author : ITVoyagers (https://itvoyagers.in)

Date :12th August 2019

Description : Write a Python program to show use of write(), writelines() and multiple write().
"""
itv=open("file1.txt","w")
itv.write("Python is easy")
itv.write("n Python is interpreted language")
lot=("n I","n love","n python")
itv.writelines(lot)
itv=open("file1.txt","r")
c=itv.read()
print(c)

OUTPUT

 
>>> 
Python is easy
 Python is interpreted language
 I
 love
 python

NOTE : Python does not have any writeline().

Practical 6k : Write a Python program to determine file position using tell().

"""
Author : ITVoyagers (https://itvoyagers.in)

Date :12th August 2019

Description : Write a Python program to determine file position using tell().
"""
with open("abc.txt","r") as g:
          s=10
          c=g.read(s)
          print("tell() returns : ",g.tell())


OUTPUT

 
>>> 
tell() returns 10
>>> 
 python

Practical 6l : Write a Python program to get file position using seek().

"""
Author : ITVoyagers (https://itvoyagers.in)

Date :12th August 2019

Description : Write a Python program to get file position using seek().
"""
with open("itvoyagers.txt","r") as f:
          s=10
          c=f.read(s)
          print("output of read(s) when s=10",c,end='n')
          #seek(0,0) will take cursor to the beginning of file
          f.seek(0,0)
          c=f.read(s)
          print("output in returned with seek(0,0)",c)
          #seek(0,1) will take cursor to the current location in the file
          f.seek(0,1)
          c=f.read(s)
          print("output in returned with seek(0,1)",c)
          #seek(0,2) will take cursor to the end of file
          f.seek(0,2)
          c=f.read(s)
          print("output in returned with seek(0,2)",c)


OUTPUT

 
>>> 
output of read(s) when s=10 
There are
output in returned with seek(0,0) 
There are
output in returned with seek(0,1)  two types
output in returned with seek(0,2) 

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