How to Check If a File Exists in Python

Before attempting to read from or write to a file in Python, it is crucial to verify its existence. Trying to access a non-existent file will raise a FileNotFoundError, crashing your script. Python provides robust tools for this, primarily via the classic os.path module and the modern pathlib object-oriented library.

This guide explains absolute versus relative paths and demonstrates two reliable methods for checking file existence.

Understanding File Paths (Absolute vs. Relative)

A file path tells the computer where a file is located.

• Absolute Path: The full address starting from the root (e.g., /home/user/project/data.txt or C:\Users\Name\data.txt). It works regardless of where your script is running.
• Relative Path: The address relative to the Current Working Directory (e.g., data.txt or ../data.txt).

import os

cwd = os.getcwd()
print(f"Current Directory: {cwd}")

filename = "my_file.txt"

abs_path = os.path.join(cwd, filename)
print(f"Absolute Path: {abs_path}")

Method 1: Using os.path.exists() (Legacy)

The standard way to check for a file or directory in older Python code is using the os.path module. It returns True if the path exists (whether it's a file or a folder) and False otherwise.

import os

filename = "my_file.txt"

if os.path.exists(filename):
    print(f"'{filename}' exists.")
else:
    print(f"'{filename}' does not exist.")

if os.path.isfile(filename):
    print("It is definitely a file.")

Method 2: Using pathlib.Path.exists() (Modern)

Introduced in Python 3.4, pathlib offers an object-oriented approach. It is generally preferred for new projects because path objects are easier to manipulate (e.g., joining paths with /) and work consistently across operating systems.

from pathlib import Path

file_path = Path("my_file.txt")

if file_path.exists():
    print(f"'{file_path}' exists.")
    
    if file_path.is_file():
        print("It is a file.")
    elif file_path.is_dir():
        print("It is a directory.")
else:
    print(f"'{file_path}' does not exist.")

Conclusion

To check if a file exists in Python:

1. Use pathlib.Path(path).exists() for modern, readable, object-oriented code.
2. Use os.path.exists(path) if working with legacy codebases.
3. Understand Paths: Remember that relative paths depend on where you run the script from (os.getcwd()).