Call a text-editor from within a Python script to get user input

Question

Motivation

I'd like to know how integrate the use of text editors (e.g. emacs, vim, etc.) into command-line Python programs.

Features

I'd like to be able to do the following:

• Call a text editor from within a program in order to edit a file or buffer

• Regain control after the text editor exits

• Use temporary files, i.e. don't leave anything lying around after the program exits

• Prepopulate the file or buffer with data

• Get the edited text back for use in the program

Implementation

I wrote a small module named callvim.py (betraying my preferred choice of text editor) which creates a temporary file, populates it with some text, opens it with a text editor (defaults to vim), and prints the modified text:

#!/usr/bin/env python
# -*- encoding: ascii -*-
"""callvim.py

Demonstrates calling a text-editor (e.g. Vim) from within a Python script,
including passing input to the editor and reading output from the editor.
"""

import tempfile
import os
from subprocess import call

# Get the text editor from the shell, otherwise default to Vim
EDITOR = os.environ.get('EDITOR','vim')

# Set initial input with which to populate the buffer
initial_message = "Hello world!"

# Open a temporary file to communicate through (`tempfile` should avoid any filename conflicts)
#
# NOTE: Don't autodelete the file on close!
#       We want to reopen the file incase the editor uses a swap-file.
#
with tempfile.NamedTemporaryFile(suffix=".tmp", delete=False) as tf:

    # Write the initial content to the file I/O buffer
    tf.write(initial_message)

    # Flush the I/O buffer to make sure the data is written to the file
    tf.flush()

    # Open the file with the text editor
    call([EDITOR, tf.name])

# Reopen the file to read the edited data
with open(tf.name, 'r') as tf:

    # Read the file data into a variable
    edited_message = tf.read()

    # Output the data
    print(edited_message)

Answer 1

click is a great library for command line processing and it has some utilities, click.edit() is portable and uses the EDITOR environment variable. I typed the line, stuff, into the editor. Notice it is returned as a string. Nice.

So, rather then write any code, you could consider replacing what your working on with these two lines:

(venv) /tmp/editor $ export EDITOR='=mvim -f'
(venv) /tmp/editor $ python
>>> import click
>>> click.edit()
'stuff\n'

Check out the docs https://click.palletsprojects.com/en/7.x/utils/#launching-editors My entire experience:

/tmp $ mkdir editor
/tmp $ cd editor
/tmp/editor $ python3 -m venv venv
/tmp/editor $ source venv/bin/activate
(venv) /tmp/editor $ pip install click
Collecting click
  Using cached https://files.pythonhosted.org/packages/fa/37/45185cb5abbc30d7257104c434fe0b07e5a195a6847506c074527aa599ec/Click-7.0-py2.py3-none-any.whl
Installing collected packages: click
Successfully installed click-7.0
You are using pip version 19.0.3, however version 19.3.1 is available.
You should consider upgrading via the 'pip install --upgrade pip' command.
(venv) /tmp/editor $ export EDITOR='=mvim -f'
(venv) /tmp/editor $ python
Python 3.7.3 (v3.7.3:ef4ec6ed12, Mar 25 2019, 16:52:21)
[Clang 6.0 (clang-600.0.57)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import click
>>> click.edit()
'stuff\n'
>>>

I would check out the source code for click.edit() if you want to write your own.

Answer 2

If I read it correctly, your edited_message would also contain your initial_message, is this expected?

I think this could be fixed by wrapping your input message this way in the file :

<Input message>

Input above this line will be ignored
###########################

<end of file>

You could then do :

edited_message = tf.read()
start_input_index = edited_message.find("###########################")

# Use the +2 to account for the \n
edited_message = edited_message[start_input_index + 2 :]

Maybe this exact code wouldn't work, I didn't test it, but the main idea is there, it would make more sense to your code.