Command Line File Downloader in Python

Python provides powerful libraries for creating command line applications. A command line file downloader allows you to download files from the internet directly through your terminal without using a browser.

This tutorial shows how to build a simple file downloader using Python's requests and argparse libraries. The application accepts a URL and filename as command line arguments and downloads the file to your local system.

Required Libraries

We need two Python libraries for this project:

• requests For making HTTP requests to download files
• argparse For handling command line arguments

Install the requests library using pip (argparse is built into Python):

pip install requests

Building the File Downloader

Step 1: Import Required Libraries

Start by importing the necessary libraries ?

import requests
import argparse

Step 2: Create the Download Function

Define a function that downloads a file from a given URL and saves it locally ?

def download_file(url, filename):
    try:
        response = requests.get(url)
        response.raise_for_status()  # Raises an HTTPError for bad responses
        
        with open(filename, "wb") as f:
            f.write(response.content)
        return True
    except requests.exceptions.RequestException as e:
        print(f"Error downloading file: {e}")
        return False

This function uses requests.get() to fetch the file content and writes it to a local file in binary mode. The with statement ensures the file is properly closed after writing.

Step 3: Parse Command Line Arguments

Set up argument parsing to handle URL and filename inputs ?

def main():
    parser = argparse.ArgumentParser(description="Download files from URLs")
    parser.add_argument("--url", help="URL of the file to download", required=True)
    parser.add_argument("--filename", help="Local filename to save as", required=True)
    
    args = parser.parse_args()
    return args

Step 4: Complete Implementation

Here's the complete command line file downloader ?

import requests
import argparse

def download_file(url, filename):
    try:
        print(f"Downloading {url}...")
        response = requests.get(url)
        response.raise_for_status()
        
        with open(filename, "wb") as f:
            f.write(response.content)
        
        print(f"File downloaded successfully as {filename}")
        return True
    except requests.exceptions.RequestException as e:
        print(f"Error downloading file: {e}")
        return False

def main():
    parser = argparse.ArgumentParser(description="Download files from URLs")
    parser.add_argument("--url", help="URL of the file to download", required=True)
    parser.add_argument("--filename", help="Local filename to save as", required=True)
    
    args = parser.parse_args()
    download_file(args.url, args.filename)

if __name__ == "__main__":
    main()

Usage Example

Save the code as downloader.py and run it from the command line ?

python downloader.py --url https://httpbin.org/json --filename sample.json

This command downloads the JSON data from httpbin.org and saves it as sample.json in your current directory.

Enhanced Features

You can extend this downloader with additional features ?

import requests
import argparse
import os
from urllib.parse import urlparse

def download_file_with_progress(url, filename=None):
    try:
        # Generate filename from URL if not provided
        if not filename:
            parsed_url = urlparse(url)
            filename = os.path.basename(parsed_url.path) or "downloaded_file"
        
        response = requests.get(url, stream=True)
        response.raise_for_status()
        
        total_size = int(response.headers.get('content-length', 0))
        downloaded = 0
        
        with open(filename, "wb") as f:
            for chunk in response.iter_content(chunk_size=8192):
                if chunk:
                    f.write(chunk)
                    downloaded += len(chunk)
                    if total_size > 0:
                        percent = (downloaded / total_size) * 100
                        print(f"\rProgress: {percent:.1f}%", end="")
        
        print(f"\nFile downloaded successfully as {filename}")
        return True
        
    except requests.exceptions.RequestException as e:
        print(f"Error downloading file: {e}")
        return False

Conclusion

Building a command line file downloader in Python is straightforward using the requests and argparse libraries. This tool provides a convenient way to download files programmatically and can be extended with features like progress bars, resume capability, and error handling for production use.