post.py

import sys
from mastodon import Mastodon
from urllib.parse import urlparse

# Replace these with your own values
instance_url = 'https://fine-instance.social'
client_id = 'also called client key'
client_secret = 'yup yup'
access_token = 'uh huh'

# Create a Mastodon API client
mastodon = Mastodon(
    client_id=client_id,
    client_secret=client_secret,
    access_token=access_token,
    api_base_url=instance_url
)

# Get the command-line arguments
args = sys.argv[1:]

if len(args) == 1:
    # Post a status update
    mastodon.status_post(args[0])
elif len(args) == 2:
    # Post a reply to an existing post
    parsed_url = urlparse(args[0])
    post_id = parsed_url.path.split('/')[-1]
    mastodon.status_post(
        args[1],
        in_reply_to_id=post_id
    )
else:
    print('Usage: python post.py [URL] "Some status"')
    print('       python post.py "Some status"')