How to Get File Extension in Python?

Best practices

Use `os.path.splitext()` to reliably get the file extension, including the dot, which helps in distinguishing files without an extension from those with one.
Prefer using `pathlib.Path.suffix` in modern Python (3.4+) for a more object-oriented approach, which directly provides the extension with the dot.
When using `split('.')` method, ensure the file name does not contain dots other than the one before the extension to avoid incorrect results.
Validate the presence of an extension after extraction to handle cases where the file might not have one, enhancing the robustness of your code.

# Import os module
import os

# Example file path
file_path = "https://sandbox.oxylabs.io/products/data.json"

# Method 1: Using os.path.splitext
extension = os.path.splitext(file_path)[1]
print("Extension using os.path.splitext:", extension) # Output: .json

# Method 2: Using split on dot and getting the last part
extension = file_path.split('.')[-1]
print("Extension using split:", extension) # Output: json

# Method 3: Using pathlib (for Python 3.4 and above)
from pathlib import Path

# Create a Path object
path = Path(file_path)

# Get the suffix
extension = path.suffix
print("Extension using pathlib:", extension) # Output: .json

Common issues

Ensure that the file path is correctly formatted and accessible before attempting to extract the extension to prevent runtime errors.
Consider using `pathlib.Path.suffixes` if dealing with files that might have multiple extensions, like `.tar.gz`, to capture all parts accurately.
When using `os.path.splitext()`, be aware that it will return an empty string as the extension for files starting with a dot unless there's another dot present.
For web URLs or paths that might contain parameters or fragments, preprocess the string to isolate the file name before extracting the extension to ensure accuracy.

# Incorrectly formatted file path
file_path = "C:\path\to\your\file.json" # Backslashes are not properly escaped
extension = os.path.splitext(file_path)[1]
print(extension) # May not work as expected

# Correctly formatted file path
file_path = r"C:\path\to\your\file.json" # Raw string to handle backslashes
extension = os.path.splitext(file_path)[1]
print(extension) # Outputs: .json

# Handling files with multiple extensions incorrectly
file_path = "archive.tar.gz"
extension = os.path.splitext(file_path)[1]
print(extension) # Outputs: .gz, misses .tar

# Handling files with multiple extensions correctly
from pathlib import Path
file_path = "archive.tar.gz"
path = Path(file_path)
extensions = path.suffixes
print(extensions) # Outputs: ['.tar', '.gz']

# Using os.path.splitext on a dotfile incorrectly
file_path = ".bashrc"
extension = os.path.splitext(file_path)[1]
print(extension) # Outputs: '', which is not expected

# Correct approach for files starting with a dot
file_path = ".bashrc"
extension = file_path.split('.')[-1] if file_path.count('.') > 1 else 'No extension'
print(extension) # Outputs: 'No extension'

# Extracting extension from a URL with parameters incorrectly
url = "http://example.com/download/file.tar.gz?download=true"
extension = os.path.splitext(url)[1]
print(extension) # Outputs: '?download=true', which is incorrect

# Correctly extracting extension from a URL
from urllib.parse import urlparse
url = "http://example.com/download/file.tar.gz?download=true"
path = urlparse(url).path
extension = os.path.splitext(path)[1]
print(extension) # Outputs: .gz