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Reading data from a file in python
Different predefined functions of Python to read data from file are::
1. read() method in Python
This function is used to read entire content of file or specific number of characters from file.
Syntax 1:
<file_object>.read()
Here file_object is the name of file handler object that is linked to a data file.
Example:
#Python Program to display entire content of text file data.txt
file1 = open(“data.txt”) #data.txt contains: I am a student s=file1.read() print(s)
Output
I am a student
** Above code will display contents of data file data,txt
Syntax 2:
<file_object>.read(N)
Here file_object is the name of file handler object that is linked to a data file.
N specified number of characters to be read from file.
Example:
file1 = open(“data.txt”) #data.txt contains: I am a student s=file1.read(6) print(s)
Output
I am a
** Above code will display first six characters (including spaces) from data file data.txt
2. readline() method in Python
This function is used to read single line at a time from an existing data file.
Syntax:
<file_object>.readline()
Here file_object is the name of file handler object that is linked to a data file.
Example 1:
#Python Program to display first line from text file data1.txt
Data file data1.txt contains following data:
This is a data file
It contains data about a student
Name of student is Amit
file1 = open(“data1.txt”) s=file1.readline() print(s)
Output
This is a data file
** Above code will display first line from data file data1.txt
Example 2:
#Python Program to display data from text data1.txt line wise.
f=open("data1.txt","r")
s=" "
while s:
s=f.readline()
print(s)
f.close()
Output
This is a data file It contains data about a student Name of student is Amit
** Above code will display complete data from file one line at a time from file data1.txt
3. readlines() method in Python
This function is used to read entire content from data file and store it in the form of a list. Each line of data file would be stored as list element.
Syntax:
<file_object>.readlines()
Here file_object is the name of file handler object that is linked to a data file.
Example:
Data file data1.txt contains following data:
This is a data file It contains data about a student Name of student is Amit
Example 1:
Program to demonstrate the use of readlines() method in Python.
file1 = open(“data1.txt”) s=file1.readlines() print(s)
Output
['This is a data file\n','It contains data about a student\n','Name of student is Amit\n']
** Above code will display data from data file data1.txt in the form of a list.
Example 2:
Python program to display the number of lines in a text file by using readlines() method in Python.
file1 = open(“data1.txt”) s=file1.readlines() count =len (s) print (“Number of lines=”, count) file1.close( )
Output
Number of lines=3
** Above code will display number of lines in data file data1.txt .
flush ( ) method in Python
When we write data into a file , Python keeps everything temporarily in buffer and saves it to actual file when close() function is called.
By using flush( ) function we can force Python to write the contents of buffer to the actual file on storage .
The syntax to use flush( ) function is :
<fileObject>. flush ( )
#Python program to demonstrate the use flush() method in Python
f = open ('newfile.txt', 'w+')
f.write ('Line 1')
f.flush( )
f.write ('Line 2')
f.flush( )
f.close( )
Other Programs
1. Python Program to read roll number and name of a students and store these details in a data file called “Marks.txt”.
Fileout = open ("Marks.txt", "a")
rollno= int (input("Enter Rollno="))
name= input ("Enter Name=")
record =str (rollno)+ "," + name + "\n"
Fileout.write(record)
Fileout.close( )
Output
Enter Rollno=101 Enter Name=aman
** Above code will read values of variables rollno and name and save it into data file Marks.txt in comma separated format. File has been opened in append mode i.e new records will be saved in the file at the end of existing file .
2. Python Program to display data saved in data file “Marks.txt” one line at a time.
Fileinput = open ("Marks.txt", "r")
s=" " #Blank space stored in string variable s.
while s :
s = Fileinput.readline( ) #Read one line at a time
print(s)
Fileinput.close ( )
Output
101,aman
3. Python Program to display data saved in data file data1.txt one word at a time.
Fileinput = open ("data1.txt", "r")
s=" "
while s :
s = Fileinput.readline( ) #Read a line from file
words=s.split() #break line into a list or words
for w in words: #Read one word at a time from list
print(w)
Fileinput.close ( )
Output
This is a data file It contains data about a student Name of student is Amit
4. Python Program to count number of words in text file data1.txt
Fileinput = open ("data1.txt", "r")
s=" "
count=0
while s :
s = Fileinput.readline( ) #Read a line from file
words=s.split() #break line into a list or words
for w in words: #Read one word at a time from list
count+=1
print("Number of words=",count)
Fileinput.close ()
Output
Number of words= 16
5. Python Program to count number of characters in data file data1.txt
Fileinput = open ("data1.txt", "r")
s=" "
count=0
while s :
s = Fileinput.read(1) #Read one character at a time.
count+=1
print("Number of characters=",count)
Fileinput.close ()
Output
Number of characters= 78
6. Python Program to count number of vowels and consonants in data file data1.txt
Fileinput = open ("data1.txt", "r")
s=" "
count=0
count1=0
while s :
s = Fileinput.read(1) #Read one character at a time.
if s in ['a','e','i','o','u']:
count+=1
else:
count1+=1
print("Number of vowels=",count)
print("Number of consonants=",count1)
Fileinput.close ()
Output
Number of vowels= 25 Number of consonants= 53
7. Python Program to add details of two students’ to the data file Marks.txt
Fileout = open (“Marks.txt”, “a”) for i in range (2) : print (“Enter details for student”, (i+1), “below :”) rollno = int(input(“Enter rollno=”)) name= input (“Enter Name=”) marks=float (input(“Enter Marks=”)) rec =str(rollno)+”,”+ name +”,”+ str(marks)+’\n’ Fileout.write(rec) Fileout.close( )
Output
>>> Enter details for student 1 below : Enter rollno :17 Name : Amit Marks : 74.6 Enter details for student 2 below : Rollno : 18 Name : John Marks : 99.2
8. Python Program to read and display details of students’ stored in data file Marks.txt .
Fileinp = open (“Marks.txt”, “r”)
while str :
str = fileinp.readline( )
print(str)
Fileinp.close ( )
Output
>>>
17,Amit , 74.6 18, John , 99.2
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