How to Check If a File Exists in Python

Introduction

In this lab, you will learn how to check if a file exists in Python using different methods. The lab begins with an introduction to file paths, explaining the difference between absolute and relative paths. You'll create a sample text file and a Python script to demonstrate how to obtain the current working directory and define both relative and absolute paths to the file.

The lab will then guide you through using the os.path.exists() function and the pathlib.Path object to verify the existence of a file. These methods provide reliable ways to determine whether a file exists before attempting to read from or write to it, preventing potential errors in your Python programs.

Skills Graph

Introduction to File Paths

In this step, we'll explore the concept of file paths in Python. Understanding file paths is crucial for reading from and writing to files, as well as for navigating your file system within your Python programs.

A file path is essentially the address of a file or directory on your computer. There are two main types of file paths:

• Absolute paths: These paths provide the complete location of a file or directory, starting from the root directory of your file system. For example, on a Linux system, an absolute path might look like /home/labex/project/my_file.txt.
• Relative paths: These paths specify the location of a file or directory relative to your current working directory. For example, if your current working directory is /home/labex/project, then the relative path my_file.txt would refer to the same file as the absolute path /home/labex/project/my_file.txt.

Let's start by creating a simple text file in your ~/project directory using the VS Code editor. Create a new file named my_file.txt and add the following content:

Hello, LabEx!
This is a test file.

Save the file in the ~/project directory.

Now, let's create a Python script to interact with this file. Create a new file named file_paths.py in the same ~/project directory and add the following code:

import os

## Get the current working directory
current_directory = os.getcwd()
print("Current working directory:", current_directory)

## Define a relative path to the file
relative_path = "my_file.txt"
print("Relative path:", relative_path)

## Define an absolute path to the file
absolute_path = os.path.join(current_directory, relative_path)
print("Absolute path:", absolute_path)

In this script:

• We import the os module, which provides functions for interacting with the operating system.
• We use os.getcwd() to get the current working directory.
• We define a relative path to the my_file.txt file.
• We use os.path.join() to combine the current working directory and the relative path to create an absolute path.

Now, let's run the script. Open your terminal in VS Code and navigate to the ~/project directory (you should already be there by default). Then, execute the script using the following command:

python file_paths.py

You should see output similar to this:

Current working directory: /home/labex/project
Relative path: my_file.txt
Absolute path: /home/labex/project/my_file.txt

This demonstrates how to obtain the current working directory and construct both relative and absolute file paths in Python. Understanding these concepts is fundamental for working with files and directories in your Python programs.

Use os.path.exists()

In this step, we'll learn how to use the os.path.exists() function to check if a file or directory exists. This is a fundamental operation when working with files, as it allows you to handle cases where a file might be missing or a directory might not be present.

The os.path.exists() function takes a single argument: the path to the file or directory you want to check. It returns True if the file or directory exists, and False otherwise.

Let's modify the file_paths.py script we created in the previous step to use os.path.exists(). Open the file_paths.py file in your VS Code editor and add the following code:

import os

## Get the current working directory
current_directory = os.getcwd()

## Define a relative path to the file
relative_path = "my_file.txt"

## Define an absolute path to the file
absolute_path = os.path.join(current_directory, relative_path)

## Check if the file exists using the relative path
if os.path.exists(relative_path):
    print("The relative path 'my_file.txt' exists.")
else:
    print("The relative path 'my_file.txt' does not exist.")

## Check if the file exists using the absolute path
if os.path.exists(absolute_path):
    print("The absolute path", absolute_path, "exists.")
else:
    print("The absolute path", absolute_path, "does not exist.")

## Check if a directory exists
directory_path = current_directory
if os.path.exists(directory_path):
    print("The directory", directory_path, "exists.")
else:
    print("The directory", directory_path, "does not exist.")

## Check if a non-existent file exists
non_existent_file = "non_existent_file.txt"
if os.path.exists(non_existent_file):
    print("The file", non_existent_file, "exists.")
else:
    print("The file", non_existent_file, "does not exist.")

In this script:

• We use os.path.exists() to check if the my_file.txt file exists, using both the relative and absolute paths.
• We also check if the current directory exists, which should always be the case.
• Finally, we check if a non-existent file exists, which should return False.

Now, let's run the script again. Open your terminal in VS Code and execute the script using the following command:

python file_paths.py

You should see output similar to this:

The relative path 'my_file.txt' exists.
The absolute path /home/labex/project/my_file.txt exists.
The directory /home/labex/project exists.
The file non_existent_file.txt does not exist.

This demonstrates how to use os.path.exists() to verify the existence of files and directories in your Python programs. This is a crucial step before attempting to read from or write to a file, as it can prevent errors and ensure that your program behaves as expected.

Verify with pathlib.Path

In this step, we'll explore the pathlib module, which provides an object-oriented way to interact with files and directories. We'll specifically focus on using pathlib.Path to verify the existence of files and directories, offering an alternative to os.path.exists().

The pathlib module offers a more modern and intuitive approach to file path manipulation compared to the older os.path module. It represents file paths as objects, allowing you to perform various operations using methods of those objects.

Let's modify the file_paths.py script we've been working with to use pathlib.Path. Open the file_paths.py file in your VS Code editor and add the following code:

import os
from pathlib import Path

## Get the current working directory
current_directory = os.getcwd()

## Define a relative path to the file
relative_path = "my_file.txt"

## Define an absolute path to the file
absolute_path = os.path.join(current_directory, relative_path)

## Create Path objects for relative and absolute paths
relative_path_obj = Path(relative_path)
absolute_path_obj = Path(absolute_path)

## Check if the file exists using the relative path object
if relative_path_obj.exists():
    print("The relative path 'my_file.txt' exists (using pathlib).")
else:
    print("The relative path 'my_file.txt' does not exist (using pathlib).")

## Check if the file exists using the absolute path object
if absolute_path_obj.exists():
    print("The absolute path", absolute_path, "exists (using pathlib).")
else:
    print("The absolute path", absolute_path, "does not exist (using pathlib).")

## Check if a directory exists using pathlib
directory_path_obj = Path(current_directory)
if directory_path_obj.exists():
    print("The directory", current_directory, "exists (using pathlib).")
else:
    print("The directory", current_directory, "does not exist (using pathlib).")

## Check if a non-existent file exists using pathlib
non_existent_file = "non_existent_file.txt"
non_existent_path_obj = Path(non_existent_file)
if non_existent_path_obj.exists():
    print("The file", non_existent_file, "exists (using pathlib).")
else:
    print("The file", non_existent_file, "does not exist (using pathlib).")

In this script:

• We import the Path class from the pathlib module.
• We create Path objects for both the relative and absolute paths to my_file.txt.
• We use the exists() method of the Path objects to check if the file exists.
• We also check for the existence of the current directory and a non-existent file using pathlib.

Now, let's run the script again. Open your terminal in VS Code and execute the script using the following command:

python file_paths.py

You should see output similar to this:

The relative path 'my_file.txt' exists (using pathlib).
The absolute path /home/labex/project/my_file.txt exists (using pathlib).
The directory /home/labex/project exists (using pathlib).
The file non_existent_file.txt does not exist (using pathlib).

This demonstrates how to use pathlib.Path as an alternative to os.path.exists() for verifying the existence of files and directories. The pathlib module offers a more object-oriented and often more readable way to interact with file paths in Python.

Summary

In this lab, we began by exploring the concept of file paths in Python, differentiating between absolute and relative paths. We learned that absolute paths provide the complete location of a file, while relative paths specify the location relative to the current working directory.

We then created a text file named my_file.txt and a Python script file_paths.py to demonstrate how to obtain the current working directory using os.getcwd() and how to define both relative and absolute paths to the created file using the os module.