Python – File Handling: Reading and Writing Files

File Handling in Python

File handling in Python involves interacting with files on your computer to read data from them or write data to them. Python provides several built-in functions and methods for creating, opening, reading, writing, and closing files. This tutorial covers the basics of file handling in Python with examples.

Opening a File in Python

To perform any file operation, the first step is to open the file. Python’s built-in open() function is used to open files in various modes, such as reading, writing, and appending. The syntax for opening a file in Python is −

file = open("filename", "mode")

File Opening Modes

Following are the file opening modes −

Once a file is opened and you have one file object, you can get various information related to that file.

Example 1

In the following example, we are opening a file in different modes −

# Opening a file in read mode
file = open("example.txt", "r")
# Opening a file in write mode
file = open("example.txt", "w")
# Opening a file in append mode
file = open("example.txt", "a")
# Opening a file in binary read mode
file = open("example.txt", "rb")

Example 2

In here, we are opening a file named “foo.txt” in binary write mode (“wb”), printing its name, whether it’s closed, and its opening mode, and then closing the file −

# Open a file
fo = open("foo.txt", "wb")
print("Name of the file: ", fo.name)
print("Closed or not: ", fo.closed)
print("Opening mode: ", fo.mode)
fo.close()

Reading a File in Python

Reading a file in Python involves opening the file in a mode that allows for reading, and then using various methods to extract the data from the file. Python provides several methods to read data from a file −

• read() − Reads the entire file.
• readline() − Reads one line at a time.
• readlines() − Reads all lines into a list.

To read a file, you need to open it in read mode. The default mode for the open() function is read mode (‘r’), but it’s good practice to specify it explicitly.

Example: Using read() Method

In the following example, we are using the read() method to read the whole file into a single string −

with open("example.txt", "r") as file:
   content = file.read()
   print(content)

Example: Using readline() Method

In here, we are using the readline() method to read one line at a time, making it memory efficient for reading large files line by line −

with open("example.txt", "r") as file:
   line = file.readline()
   while line:
      print(line, end='')
      line = file.readline()

Example: Using readlines() Method

Now, we are using the readlines() method to read the entire file and splits it into a list where each element is a line −

with open("example.txt", "r") as file:
   lines = file.readlines()
   for line in lines:
      print(line, end='')

Writing to a File in Python

Writing to a file in Python involves opening the file in a mode that allows writing, and then using various methods to add content to the file.

To write data to a file, use the write() or writelines() methods. When opening a file in write mode (‘w’), the file’s existing content is erased.

Example: Using the write() Method

In this example, we are using the write() method to write the string passed to it to the file. If the file is opened in ‘w’ mode, it will overwrite any existing content. If the file is opened in ‘a’ mode, it will append the string to the end of the file −

with open("foo.txt", "w") as file:
   file.write("Hello, World!")
   print("Content added Successfully!!")

Example: Using the writelines() Method

In here, we are using the writelines() method to take a list of strings and writes each string to the file. It is useful for writing multiple lines at once −

lines = ["First line\n", "Second line\n", "Third line\n"]
with open("example.txt", "w") as file:
   file.writelines(lines)
   print("Content added Successfully!!")

Closing a File in Python

We can close a file in Python using the close() method. Closing a file is an essential step in file handling to ensure that all resources used by the file are properly released. It is important to close files after operations are completed to prevent data loss and free up system resources.

Example

In this example, we open the file for writing, write data to the file, and then close the file using the close() method −

file = open("example.txt", "w")
file.write("This is an example.")
file.close()
print("File closed successfully!!")

Using “with” Statement for Automatic File Closing

The with statement is a best practice in Python for file operations because it ensures that the file is automatically closed when the block of code is exited, even if an exception occurs.

with open("example.txt", "w") as file:
   file.write("This is an example using the with statement.")
   print("File closed successfully!!")

Handling Exceptions When Closing a File

When performing file operations, it is important to handle potential exceptions to ensure your program can manage errors gracefully.

In Python, we use a try-finally block to handle exceptions when closing a file. The “finally” block ensures that the file is closed regardless of whether an error occurs in the try block −

try:
   file = open("example.txt", "w")
   file.write("This is an example with exception handling.")
finally:
   file.close()
   print("File closed successfully!!")

Key Takeaway: Master file handling with open(), reading methods (read(), readline()), writing (write()), and safe closing—essential skills for file operations!