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In our last article, we have explained how to write to a file on the disk. In this tutorial, we are going to explain how to append new data at the end of an existing file on disk. But before we perform the append operation on a file, we must open it.

For this, the Python language provides us a function named open(), using which we open a the file in a specific mode in order to perform file append operation.

• Calling the open() function to open a file to append to it


In order to open a file to perform the append operation, we could call the open() function of io module, which is a default module for performing file operations. Using the open() function, we could provide location of the file stored on the disk and in return(if the file is found), the open() function opens the file in a mode of your choice, to let you perform the specific operation.

Let us take a look at a general syntax of open() function to open a file.



open('filename', mode);



• filename(a string value), is the name of file on which we are going to open and perform a specific file operation.
• mode(a string value), is a single or multiple file modes in which we are going to open a file.

Let's read about the required file mode value, to append new content to the end of a file.






• Mode to append to a file


Let's look at the mode required to write a file.



File Mode	Description
a	Searches for the file and opens it in append mode i.e. this mode allows you to append new data to the end of a file. If file is not found, a new file is created. Allows you to append to the file by setting the cursor position to the end of file.








• Methods to append to a file


We can append new content to the end of a file using the methods available to all the file objects. Let us take a look at these methods.



Methods	Description
write(str)	The write() method writes and appends a string(str) value to the end of file.
writelines(lines)	The writelines() method writes and appends a list of lines to the end of a file.






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• Appending to a file using write() method


Let's say that we already have an existing file on disk, named File1.txt, with content :



Greetings! Hope you are doing well. 


Now let's try to write and append data to this file by taking input from an already initialized strings using the write(str) method. This file will be searched in the current directory(the same directory where we are going to store the upcoming Python program.).




# Python - Appending new data to a file using the write() method.
 


# Calling the open() function to open a file named File1.txt in write mode
file = open('File1.txt', 'a')


# Creating 3 strings and appending the newline character \n at their beginning of each string
# to make the appended string appear in the new line.
str1 = '\n' + 'Never give up and keep learning.'
str2 = '\n' + 'Keep smiling :-)'


# Writing the first string value to the file using the write() method of file object
file.write(str1)


# Writing the second value to the file using the write() method of file object
file.write(str2)


# Closing the file after completing the write operation on it
file.close()




Output


Executing this program will create a file named File1.txt in the current directory, with its content-



Greetings! Hope you are doing well.
Never give up and keep learning
Keep Smiling :-)








• Appending to a file by taking input from user at console


Let's say that we already have an existing file on disk, named File2.txt, with content :



Fun facts!


Let us see a code to write and append to a file on disk by taking input from the user at the console, using the built-in input() function This file will be searched in the current directory(the same directory where we are going to store the upcoming program.)



# Python - Appending new data to the file by taking input from the user.
 


# Calling the open() function to open a file named File2.txt in write mode
file = open('File2.txt', 'a')


# Creating 3 strings
str1 = input('Which month has 28 days? : ')
str2 = input('What is the color of a block box on an airplane : ')
str3 = input('What comes down but never goes up? : ')


# Writing the first string value to the file using the write() method of file object 
# Also, appending the newline character \n at their beginning of each string
# to make the appended string appear in the new line.
file.write('\n' + str1)


# Writing the second value to the file using the write() method of file object
file.write('\n' + str2)


# Writing the third string value to the file using the write() method of file object
file.write('\n' + str3)


# Closing the file after completing the write operation on it
file.close()




Output




Which month has 28 days? : All months have 28 days :-)
What is the color of a block box on an airplane : The color of black box is always bright, so it is easy to find it.
What comes down but never goes up? : Rain always comes down, does it ever go up? Nah :-)



Executing this program will append the data entered by the user at the console at the end of a file named File2.txt in the current directory. Let's see the content of this file


File2.txt

Fun Facts!
All months have 28 days :-)
The color of black box is always bright, so it is easy to find it.
Rain always comes down, does it ever go up? Nah :-)








• Appending to a file using writelines() method


Let's say that we already have an existing file on disk, named File3.txt, with content :



All work and no plan could make Jack a dull boy!


Let us see a program to write and append a list of lines(where each line is a string value), to the end of a file on disk usign using writelines() method.



# Python - Appending lines to a file.
 


# Calling the open() function to open a file named File3.txt in write mode
file = open('File7.txt', 'a')


# Creating 3 strings and appending the newline character \n at their beginning
# To make the appended string appear in the new line.
str1 = '\n' + 'Hello World!'
str2 = '\n' + 'Can you answer a question?'
str3 = '\n' + 'Which came first - Chicken or Egg?'


# Creating a list of lines, where each line is a string value.
a_list = [str1, str2, str3]


# Writing a list of lines to the file using the writelines() method of file object
file.writelines(a_list)


# Closing the file after completing the write operation on it
file.close()




Output


Executing this program will append some new content to the end of a file named File3.txt in the current directory, with its content looking like :



All work and no plan could make Jack a dull boy!
Hello World! 
Can you answer a question? 
Which came first - Chicken or Egg? 








• Using a+ mode to append and read a file


We can even use the a+(append plus read mode), which allows us to not just append to a file but also read its content. Let's say that we already have an existing file on disk, named File4.txt, with content :



Hello there!


Let us see a program to first read the file and then append a string to the end of a file on disk usign a+ file mode.

Note: By default the a file mode(or a+ mode), allows you to append to the file by setting the cursor position to the end of file, therefore in order to read the file in an append mode, we will have to use seek() method of file object, to set the cursor position to the beginning of the file, so we could read the file from the beginning. Let us see how it is done.



# Python - Modifying a file
 
import os



# Calling the open() function to open a file named File3.txt in append + read mode
file = open('File11.txt', 'a+')



# os.SEEK_SET = sets the cursor  to the beginning of the file
# os.SEEK_CUR = sets the cursor  to the current position in the file
# os.SEEK_END = sets the cursor  to the end position in the file
# Setting the cursor position to zero bytes from the beginning of the file
# So we could read the file from the beginning.
file.seek(0, os.SEEK_SET)



# Calling the read() method for file objects, to read all its content.
print('File content before appending : ')
print(file.read())



# Creating a string and appending the newline character \n at their end
str1 = 'Ting Tong!'



# Writing a string to the file using the write() method of file object
file.write(str1)


# Calling the seek method to set the cursor position to Zeroth bytes from the beginning of the file
# os.SEEK_SET = sets the cursor  to the beginning of the file
# os.SEEK_CUR = sets the cursor  to the current position in the file
# os.SEEK_END = sets the cursor  to the end position in the file
file.seek(0, os.SEEK_SET)



# Calling the read() method for file objects, to read all its content after appending data to it
print('File content before appending : ')
print(file.read())



# Closing the file after completing the write operation on it
file.close()




Output


Executing this program will append some new content to the end of a file named File3.txt in the current directory, with its content looking like :



File content before appending : 
Hello World. Keep Smiling!
File content after appending :
Hello World. Keep Smiling!Ting Tong! 



In the next tutorial, we are going to explain how to modify the content of an existing file.






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