Text File Handling in Python

File Handling in Python

What is Text File Handling

Text File Handling is a process in which we create a text file and store data permanently on a hard disk so that it can be retrieved from the memory later for use in a program.

In a text file, whatever data we store is treated as text. Even if we store numbers, it is treated as text.

Operation on Text File

There are different types of operations that we can perform on a text file, they are:

• Opening and Closing a Text File.
• Write to a file.
• Read from a file.
• Copy a file from one location to another.
• Rename a file.
• Delete a file.

Text File Opening Modes

Below we have discussed the different types of text file opening modes used to open a text file in python.

Open a text file

We use open() function to open a text file in python. The syntax is given below.

file_object = open('file_name', 'access_mode')

In the above syntax, file_object is the variable's name in which the file handle will be stored as an object. The file_name is the name of the file along with its path. The access_mode is the mode which is used while opening a file..

fileobj = open('D:/data.txt','w+')

In the above statement, the file data.txt is opened in reading and writing modes under D drive in the windows operating system. The file pointer will stand at the beginning of the file. That means we can write data, and at the same time, we can also read data from the file using the file object named fileobj.

Open a text file using with statement

In python, we can also open a text using a with statement. The syntax is given below.

with open('file_name', 'access_mode') as file_object:

with open('D:/data.txt','w+') as fileobj:
    fileobj.write('Hello World')

The advantage of using a with statement while opening a file is that it ensures that the file will close automatically when the program comes out of the with block. This way the user don't have to close the file explicitly.

Close a file

We use the close() method to close a file in python. Any unsaved data is written to the file before it is closed.

file_object.close():

fileobj = open('D:/data.txt','w+')
fileobj.close()

Writing to a text file

To write data in a text file, first, we have to open the file either in write or append mode. If we open an existing file in write mode, the previous data will be erased, and the file pointer will stand at the beginning of the file.

If the file already exists, we will open the file in append mode so the file pointer will stand at the end, and we can add new data to the file. In append mode, the previous data is not erased.

There are two methods that we can use to write data in a text file, and they are:

• write()
• writelines()

write() Method

The write() method is used to write a string in an opened file. This method does not automatically add a newline character (\n) at the end of the string. We need to manually add the newline character (\n) at the end of the string to mark the end of the line.

with open('D:/data.txt','w+') as fileobj:
    print('Enter five animals names')
    for i in range(5):
        name=input('Enter the animal name: ')
        fileobj.write(name)
        fileobj.write('\n')

Enter five animals names
Enter the animal name: Dog
Enter the animal name: Cat
Enter the animal name: Mouse
Enter the animal name: Elephant
Enter the animal name: Horse

writelines() Method

The writelines() method is used to write a list of strings in an opened file. Like the write() method, this method does not automatically add a newline character (\n) at the end of the string. We need to manually add the newline character (\n) at the end of the string to mark the end of the line.

with open('D:/countries.txt','w+') as fileobj:
    print('Enter five countries names')
    country = []    # An emplty list
    for i in range(5):
        name=input('Enter the country name: ')
        country.append(name + '\n')

    fileobj.writelines(country)

Enter five countries names
Enter the country name: America
Enter the country name: India
Enter the country name: Korea
Enter the country name: Japan
Enter the country name: Australia

Reading from a text file

To read data from a text file, we have to open the file in read mode.

There are three methods that we can use to read data from a text file, and they are:

• read()
• readline(n)
• readlines()

read() Method

The read() method reads a specified number of bytes of data from a file. The entire file content is read if the number of bytes is not given.

with open('D:/countries.txt','r') as fileobj:
    # read 5 bytes from the file
    data = fileobj.read(5)
    print(data)

    # read the entire content of the file
    data = fileobj.read()
    print(data)

Ameri
ca
India
Korea
Japan
Australia

In the above program, we first read 5 bytes (characters) from the file, so it reads up to Ameri, and the file pointer stands after i in the file. Later we read the entire file content, so it starts reading from ca to Australia.

readline(n) Method

The readline(n) method reads one complete line from a file that terminates with a newline (\n) character. It can also read a specified number of bytes from a file but ends reading when a newline (\n) character is found while reading the specified number of bytes.

with open('D:/countries.txt','r') as fileobj:
    # read the first line from the file
    data = fileobj.readline()
    print(data)

    # read 10 bytes from the file
    data = fileobj.readline(10)
    print(data)

America

India

readlines() Method

The readlines() method reads all the lines from the file, including the newline (\n) character, and returns the lines as a list of strings.

with open('D:/countries.txt','r') as fileobj:
    # read all the lines from the file including the newline (\n) character
    data = fileobj.readlines()
    print(data)

['America\n', 'India\n', 'Korea\n', 'Japan\n', 'Australia\n']

We can use the for loop to print all the lines on the screen. See the example given below.

with open('D:/countries.txt','r') as fileobj:
    # read all the lines from the file
    data = fileobj.readlines()

    # print all the lines on the screen using the for loop
    for line in data:
        print(line, end='')

America
India
Korea
Japan
Australia

In the above program, the line is a variable that reads each element from the list data and prints it on the screen.

Setting file pointer (cursor)

To read a file randomly, we need to place the file pointer (cursor) in a file at the specified location so we can read characters from that location onwards. To do so, python provides two methods to work with the file pointer, and they are:

• tell()
• seek()

tell() Method

The tell() method returns an integer that specifies the position of the file pointer in a file. The position specifies the number of bytes the file pointer is standing at from the beginning of the file.

with open('D:/countries.txt','r') as fileobj:
    # read 5 bytes from the beginning of the file
    data = fileobj.read(5)
    print(data)

    # print the file pointer position in the file
    x = fileobj.tell()
    print('The file pointer is standing at position %d in the file' %(x))

    # read next byte from the file
    data = fileobj.read(1)
    print(data)

    # print the file pointer position in the file
    x = fileobj.tell()
    print('The file pointer is standing at position %d in the file' %(x))

Ameri
The file pointer is standing at position 5 in the file
c
The file pointer is standing at position 6 in the file

After reading 5 bytes from the file in the above program, the file pointer stands at the 5th position (at i in the file). So the next byte in the file after i is c. When we read one more byte from the file, it reads the character c, and then the file pointer stands at position 6.

seek() Method

The seek() method sets the file pointer at a specific position in a file. Using the seek() method, we can move the file pointer in a file either forward or backwards. The syntax is given below.

fileobj.seek(offset, whence)

Here the offset is the number of bytes to move forward or backwards in the file from the whence arguments. The whence argument specifies from which position the file pointer should move forward or backwards in the file.

The whence argument provides the following values.

• 0 means moving the file pointer from the beginning of the file.
• 1 means moving the file pointer from the current position in file position.
• 2 means moving the file pointer from the end of the file.

The default value of the whence argument is 0, which means from the beginning of the file.

See the examples below to clearly understand how to implement the seek() method in file handling.

with open('D:/countries.txt','r') as fileobj:
    # read 5 bytes from the beginning of the file
    data = fileobj.read(5)
    print(data)

    # move file pointer to the beginning of the file
    fileobj.seek(0)

    # read a complete line from the beginning of the file
    data = fileobj.readline()
    print(data)

Ameri
America

with open('D:/countries.txt','r+') as fileobj:
    # move file pointer to the end of the file
    fileobj.seek(0,2)

    # write canada at the end of the file
    fileobj.write('Canada\n')

    # move file pointer to the beginning of the file
    fileobj.seek(0)

    # read the complete content of the file
    data = fileobj.read()
    print(data)

America
India
Korea
Japan
Australia
Canada

with open('D:/countries.txt','r') as fileobj:
    # move the file pointer 10 bytes ahead from the beginning of the file
    fileobj.seek(10)

    # now read 8 bytes
    data = fileobj.read(8)
    print(data)

ndia
Kor

with open('D:/countries.txt','r') as fileobj:
    # read 36 bytes from the file
    data = fileobj.read(36)
    print(data)

    # move the file pointer 11 bytes backward from the current location in the file
    fileobj.seek(fileobj.tell()-11)

    # now read the full content of the file from the current location onwards
    data = fileobj.read()
    print(data)

America
India
Korea
Japan
Australia

Australia
Canada

Note: If the file is opened in non-binary mode (without using b in the access mode), then we can't move the file pointer backwards with a negative value from the current location in the file. If we do so, it will give the following error, as shown below.

with open('D:/countries.txt','r') as fileobj:
    # read 36 bytes from the file
    data = fileobj.read(36)
    print(data)

    # move the file pointer 11 bytes backward from the current location in the file
    fileobj.seek(-11,1)

    # now read the full content of the file from the current location onwards
    data = fileobj.read()
    print(data)

Traceback (most recent call last):
  File "D:\python\example.py", line 7, in 
    fileobj.seek(-11,1)
io.UnsupportedOperation: can't do nonzero cur-relative seeks

We have to open the file in binary mode to move the file pointer backwards with a negative value. See the example given below.

with open('D:/countries.txt','rb') as fileobj:
    # read 36 bytes from the file
    data = fileobj.read(36).decode('utf-8')
    print(data)

    # move the file pointer -11 bytes backward from the current location in the file
    fileobj.seek(-11,1)

    # now read the full content of the file from the current location onwards
    data = fileobj.read().decode('utf-8')
    print(data)

America
India
Korea
Japan
Austra
pan
Australia
Canada

The newline character in binary mode in the above program is \r\n. So 36 bytes will end at Austra, where \r\n is included at the end of each line. Now moving backwards, -11 bytes will move the file pointer to the pan of Japan. When we are reading the entire content of the file from the current location, this will print the content starting from pan to Canada.

The decode('utf-8') converts the text into readable format. Without it, the content will look as shown below.

with open('D:/countries.txt','rb') as fileobj:
    # read 36 bytes from the file
    data = fileobj.read(36)
    print(data)

    # move the file pointer -11 bytes backward from the current location in the file
    fileobj.seek(-11,1)

    # now read the full content of the file from the current location onwards
    data = fileobj.read()
    print(data)

b'America\r\nIndia\r\nKorea\r\nJapan\r\nAustra'
b'pan\r\nAustralia\r\nCanada\r\n'

In the above output, b at the beginning of each line represents the string into binary format, and \r\n represents the newline characters in the binary format.

Write multiple lines in a file

Let's write a program where we will create a file and write multiple lines in it.

# create the file record.txt at D:/ drive
with open('D:/record.txt','a+') as fileobj:

    # write some text in the file and press enter key twice to end writing
    print('Write some text and press enter key twice to end writing')
    data = input()
    while len(data)>0:
        fileobj.write(data+'\n')
        data = input()

    # move the file pointer to the beginning of the file
    fileobj.seek(0)

    # read the full content of the file
    data = fileobj.read()
    print(data)

Write some text and press enter key twice to end writing
We are learning text file handling in python.
We have create a file record.txt and writing this text in it.

We are learning text file handling in python.
We have create a file record.txt and writing this text in it.

Copy a file from one location to another

To copy a file from one location to another, we need to use the shutil.copy() method. This method is available in the shutil module.

import shutil

src_file = r'D:\countries.txt'
dest_file = r'E:\countries.txt'
shutil.copy(src_file, dest_file)
print('File Copied Successfully')

File Copied Successfully

Rename a file

We need to use the os.rename() method to rename a file. This method is available in the os module.

import os

old_name = r'D:\countries.txt'
new_name = r'D:\countries2.txt'
os.rename(old_name, new_name)
print('File Renamed Successfully')

File Renamed Successfully

Delete a file

We need to use the os.remove() method to delete a file. This method is available in the os module.

import os

file_name = r'D:\countries2.txt'
os.remove(file_name)
print('File Deleted Successfully')

File Deleted Successfully