Understanding Python’s open() Function: A Comprehensive Guide

In this tutorial, we will delve into the usage of Python’s built-in open() function. This function is used to open a file in either read, write or append mode.

Basic Usage of open()

The basic syntax for using the open() function is as follows:

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

The “filename” is a string that represents the name (and path if not in the same directory) of the file you want to access. The “mode” is another string that defines which mode you want to open the file in. There are several modes available but here are three most commonly used ones:

  • “r”: Read mode which is used when the file is only being read
  • “w”: Write mode which is used to edit and write new information to the file
  • “a”: Append mode, which is used to add new data to the end of the file

Detailed Walkthrough

Opening a File in Read Mode

file = open("test.txt", "r")

This code opens “test.txt” in read mode, prints its contents on screen and then closes it.

Opening a File in Write Mode

file = open("test.txt", "w")
file.write("Hello World!")

This code opens “test.txt” in write mode, writes ‘Hello World!’ into it and then closes it. If “test.txt” didn’t exist before, it will be created.

Opening a File in Append Mode

file = open("test.txt", "a")
file.write("\nHello again!")

This code opens “test.txt” in append mode and adds ‘Hello again!’ to the end of its contents. The ‘\n’ character is used to add a new line before our appended text.


The open() function is a powerful tool for handling files in Python. It’s important to remember to close your files after you’re done with them, as not doing so can lead to data loss or corruption. Happy coding!

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