exercise-8-4.md

Exercise 8-4: Find the Largest Files in Any Dataset

This exercise teaches you to use the [Click])(https://click.palletsprojects.com/) module to make CLI programs in Python.

You can find my solution for this exercise assignment in exercise-8-4.py.

If you haven't installed click yet, install it with pip:

python3 -m pip install click

In this solution, the Python script starts by importing the two modules that we need, os and click:

import os
import click

It then defines the main() function as a Click command. It takes a path argument, and it takes a password option. Click is smart enough so that, when the main() function is called, it passes in path and password as arguments to the function.

@click.command()
@click.argument("path")
@click.option("--password", prompt="Enter password", help="Password is required")
def main(path, password):
    """Get information about files and folders"""

Just this code alone will create the help text for this CLI command:

micah@trapdoor chapter-8 % python3 exercise-8-4.py --help         
Usage: exercise-8-4.py [OPTIONS] PATH

  Get information about files and folders

Options:
  --password TEXT  Password is required
  --help           Show this message and exit.

The first requirement is make sure the password is yourefired, and if it's not quit with an error message. Here's the code that does that:

    # Make sure the password is valid
    if password != "yourefired":
        click.echo("Access Denied")
        return

Just calling return will quit from the main() function early. If the password is anything except yourefired, the script quits early:

micah@trapdoor chapter-8 % python3 exercise-8-4.py click-example.py --password letmein
Access Denied

The next step is to make sure that path is an actual valid path:

    # Make sure the path is valid
    if not os.path.exists(path):
        click.echo("Error: Invalid path")
        return

If the path doesn't exist, it displays an error and quits early.

If we've made it past this check, we know for sure that it's a valid path. So the next step is to check to see if it's a file or a folder. In this solution I'm just using an if statement to check if os.path.isfile(path) is True. If it's false, the code assumes that it's a folder, and the else block runs.

    # See if the path is a file
    if os.path.isfile(path):
        # Display information about this file
        # -

    # See if the path is a folder
    else:
        # Display information about this folder
        # --snip--

If the path is a file, the code looks up the file size and displays this information:

        # Display information about this file
        file_size = os.path.getsize(path)
        click.echo(f"{path} is a file that is {file_size} bytes.")

If it's a folder, it's slightly more complicated. First, it loops through the output of os.listdir(path), which is a list of all the files in the folder. Then for each filename in the output, if it's a file it displays the filename and its file size, and if it's a folder it just displays its filename:

        # Display information about this folder
        click.echo(f"{path} is a folder. Here are the files inside it:")
        for filename in os.listdir(path):
            if os.path.isfile(os.path.join(path, filename)):
                file_size = os.path.getsize(os.path.join(path, filename))
                click.echo(f"- FILE: {filename} ({file_size} bytes)")
            else:
                click.echo(f"- FOLDER: {filename}")

Here is the script in action. In my case, I don't have a file called does-not-exist in my working folder, and I have a file called Docker.dmg and a few other files, and a folder called old, in my Downloads folder.

micah@trapdoor chapter-8 % python3 exercise-8-4.py does-not-exist
Enter password: letmein
Access Denied
micah@trapdoor chapter-8 % python3 exercise-8-4.py does-not-exist
Enter password: yourefired
Error: Invalid path
micah@trapdoor chapter-8 % python3 exercise-8-4.py ~/Downloads/Docker.dmg
Enter password: yourefired
/Users/micah/Downloads/Docker.dmg is a file that is 589068342 bytes.
micah@trapdoor chapter-8 % python3 exercise-8-4.py ~/Downloads/ --password yourefired
/Users/micah/Downloads/ is a folder. Here are the files inside it:
- FILE: .DS_Store (6148 bytes)
- FILE: .localized (0 bytes)
- FOLDER: old
- FILE: Docker.dmg (589068342 bytes)