Reading and Writing to text files in Python

Python provides built-in functions for creating, writing, and reading files. Two types of files can be handled in Python, normal text files and binary files (written in binary language, 0s, and 1s).

• Text files: In this type of file, Each line of text is terminated with a special character called EOL (End of Line), which is the new line character (‘\n’) in Python by default.
• Binary files: In this type of file, there is no terminator for a line, and the data is stored after converting it into machine-understandable binary language.

This article will focus on opening, closing, reading, and writing data in a text file. Here, we will also see how to get Python output in text file.

File Access Modes

Access modes govern the type of operations possible in the opened file. It refers to how the file will be used once its opened. These modes also define the location of the File Handle in the file. The file handle is like a cursor, which defines from where the data has to be read or written in the file and we can get Python output in text file.

There are 6 access modes in Python:

• Read Only (‘r’)
• Read and Write (‘r+’)
• Write Only (‘w’)
• Write and Read (‘w+’)
• Append Only (‘a’)
• Append and Read (‘a+’)

Read Only (‘r’) : Open text file for reading. The handle is positioned at the beginning of the file. If the file does not exist, raises the I/O error. This is also the default mode in which a file is opened.

Read and Write (‘r+’): Open the file for reading and writing. The handle is positioned at the beginning of the file. Raises I/O error if the file does not exist.

Write Only (‘w’) : Open the file for writing. For the existing files, the data is truncated and over-written. The handle is positioned at the beginning of the file. Creates the file if the file does not exist.

Write and Read (‘w+’) : Open the file for reading and writing. For an existing file, data is truncated and over-written. The handle is positioned at the beginning of the file.

Append Only (‘a’): Open the file for writing. The file is created if it does not exist. The handle is positioned at the end of the file. The data being written will be inserted at the end, after the existing data.

Append and Read (‘a+’) : Open the file for reading and writing. The file is created if it does not exist. The handle is positioned at the end of the file. The data being written will be inserted at the end, after the existing data.

How Files are Loaded into Primary Memory?

There are two kinds of memory in a computer i.e. Primary and Secondary memory every file that you saved or anyone saved is on secondary memory cause any data in primary memory is deleted when the computer is powered off. So when you need to change any text file or just to work with them in python you need to load that file into primary memory. Python interacts with files loaded in primary memory or main memory through “file handlers” ( This is how your operating system gives access to python to interact with the file you opened by searching the file in its memory if found it returns a file handler and then you can work with the file ).

Opening a Text File in Python

It is done using the open() function. No module is required to be imported for this function.

File_object = open(r"File_Name","Access_Mode")

The file should exist in the same directory as the python program file else, the full address of the file should be written in place of the filename. Note: The r is placed before the filename to prevent the characters in the filename string to be treated as special characters. For example, if there is \temp in the file address, then \t is treated as the tab character, and an error is raised of invalid address. The r makes the string raw, that is, it tells that the string is without any special characters. The r can be ignored if the file is in the same directory and the address is not being placed. 

# Open function to open the file "MyFile1.txt"
# (same directory) in append mode and
file1 = open("MyFile1.txt","a")

# store its reference in the variable file1
# and "MyFile2.txt" in D:\Text in file2
file2 = open(r"D:\Text\MyFile2.txt","w+")

Here, file1 is created as an object for MyFile1 and file2 as object for MyFile2

Closing a Text File in Python

close() function closes the file and frees the memory space acquired by that file. It is used at the time when the file is no longer needed or if it is to be opened in a different file mode. File_object.close() 

# Opening and Closing a file "MyFile.txt"
# for object name file1.
file1 = open("MyFile.txt","a")
file1.close()

Writing to a file in Python

There are two ways to write in a file:

• Using write()
• Using writelines()

Writing to a Python Text File Using write()

write() : Inserts the string str1 in a single line in the text file.

File_object.write(str1)

Writing to a Text File Using writelines()

writelines() : For a list of string elements, each string is inserted in the text file.Used to insert multiple strings at a single time.

File_object.writelines(L) for L = [str1, str2, str3]

Reference: write() VS writelines()

Reading from a file in Python

There are three ways to read data from a text file:

• Using read()
• Using readline()
• Using readlines()

Reading From a File Using read()

read() : Returns the read bytes in form of a string. Reads n bytes, if no n specified, reads the entire file.

File_object.read([n])

Reading a Text File Using readline()

readline() : Reads a line of the file and returns in form of a string.For specified n, reads at most n bytes. However, does not reads more than one line, even if n exceeds the length of the line.

File_object.readline([n])

Reading a File Using readlines()

readlines() : Reads all the lines and return them as each line a string element in a list.

  File_object.readlines()

Note: ‘\n’ is treated as a special character of two bytes.

In this example, a file named “myfile.txt” is created and opened in write mode ("w"). Data is written to the file using write and writelines methods. The file is then reopened in read and append mode ("r+"). Various read operations, including read, readline, readlines, and the use of seek, demonstrate different ways to retrieve data from the file. Finally, the file is closed.

# Program to show various ways to read and
# write data in a file.
file1 = open("myfile.txt", "w")
L = ["This is Delhi \n", "This is Paris \n", "This is London \n"]

# \n is placed to indicate EOL (End of Line)
file1.write("Hello \n")
file1.writelines(L)
file1.close()  # to change file access modes

file1 = open("myfile.txt", "r+")

print("Output of Read function is ")
print(file1.read())
print()

# seek(n) takes the file handle to the nth
# byte from the beginning.
file1.seek(0)

print("Output of Readline function is ")
print(file1.readline())
print()

file1.seek(0)

# To show difference between read and readline
print("Output of Read(9) function is ")
print(file1.read(9))
print()

file1.seek(0)

print("Output of Readline(9) function is ")
print(file1.readline(9))

file1.seek(0)
# readlines function
print("Output of Readlines function is ")
print(file1.readlines())
print()
file1.close()

Output:

Output of Read function is 
Hello 
This is Delhi 
This is Paris 
This is London 
Output of Readline function is 
Hello 
Output of Read(9) function is 
Hello 
Th
Output of Readline(9) function is 
Hello 
Output of Readlines function is 
['Hello \n', 'This is Delhi \n', 'This is Paris \n', 'This is London \n']

Appending To a File in Python

In this example, a file named “myfile.txt” is initially opened in write mode ("w") to write lines of text. The file is then reopened in append mode ("a"), and “Today” is added to the existing content. The output after appending is displayed using readlines. Subsequently, the file is reopened in write mode, overwriting the content with “Tomorrow”. The final output after writing is displayed using readlines.

# Python program to illustrate
# Append vs write mode
file1 = open("myfile.txt","w")
L = ["This is Delhi \n","This is Paris \n","This is London \n"]
file1.writelines(L)
file1.close()

# Append-adds at last
file1 = open("myfile.txt","a")#append mode
file1.write("Today \n")
file1.close()

file1 = open("myfile.txt","r")
print("Output of Readlines after appending")
print(file1.readlines())
print()
file1.close()

# Write-Overwrites
file1 = open("myfile.txt","w")#write mode
file1.write("Tomorrow \n")
file1.close()

file1 = open("myfile.txt","r")
print("Output of Readlines after writing")
print(file1.readlines())
print()
file1.close()

Output:

Output of Readlines after appending
['This is Delhi \n', 'This is Paris \n', 'This is London \n', 'Today \n']
Output of Readlines after writing
['Tomorrow \n']

Related Article:

• File Objects in Python 

Reading and Writing to text files in Python – FAQs

Which methods are used for reading and writing files in Python?

• For reading files: read(), readline(), readlines()
• For writing files: write(), writelines()

How to read a file and write to another file in Python?

You can achieve this by opening two files: one for reading and another for writing, and then using appropriate methods to read from one file and write to another.

# Read from 'input.txt' and write to 'output.txt'
with open('input.txt', 'r') as file_in:
    with open('output.txt', 'w') as file_out:
        for line in file_in:
            file_out.write(line)

What is the difference between reading and writing files in Python?

• Reading files: Involves methods (read(), readline(), readlines()) to retrieve data from a file.
• Writing files: Involves methods (write(), writelines()) to store data into a file.

Which function is used to read data from a text file?

The read() method is commonly used to read data from a text file in Python.

with open('file.txt', 'r') as file:
    data = file.read()
    print(data)

What is file.read() in Python?

file.read() is a method in Python used to read the entire contents of a file as a string. It reads from the current position until the end of the file or until a specified number of bytes.

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