Full code listing for a blogpost of mine - https://alcarney.me/2019/01/05/til-python-cmd.html

stylo-cmd.py

import cmd
import textwrap
import matplotlib.pyplot as plt

from stylo import __version__
from stylo.color import FillColor
from stylo.image import LayeredImage
from stylo.shape import Circle, Square


intro_text = """\
Interactive Shell for Stylo v{}
----------------------------------

Type `q` or `Ctrl-D` to quit.
Type `help` or `?` for an overview `help <command>` for more details.
"""

doc_text = """\
Interactive Shell for Stylo v{}
-------------------------------

This is an interactive shell interface to the Stylo Python package.

Commands:
---------
"""


class StyloPrompt(cmd.Cmd):

    prompt = "-> "
    ruler = ""
    intro = intro_text.format(__version__)
    doc_header = doc_text.format(__version__)

    def __init__(self):
        super().__init__()
        self.image = LayeredImage()

        self.fig, self.ax = plt.subplots(1, figsize=(12, 12))
        self.ax.get_yaxis().set_visible(False)
        self.ax.get_xaxis().set_visible(False)

        self.update_image()

    def do_reset(self, args):
        """reset <size> <color>

        Reset the image back to a blank canvas with a given <size>
        and background <color>.

        The <size> parameter is a dimensionless scale applied to the image
        and corresponds to the distance between the top and bottom of the
        image.

        The <color> parameter is a 6 digit hex number which represents the
        color in RGB format.

        Example:

        -> reset 2.5 00aaff
        """

        size, color = args.split(" ")

        size = float(size)

        self.image = LayeredImage(background=color, scale=size)

    def do_save(self, args):
        """save <width> <height> <filename>

        Save the current image to <filename> with a given <width> and
        <height>. Dimensions are in pixels.

        Example:

        -> save 1920 1080 image.png
        """

        width, height, filename = args.split(" ")

        width = int(width)
        height = int(height)

        self.image(width, height, filename=filename)

    def do_circle(self, args):
        """circle <x> <y> <r> <color>

        This command will draw a circle centered at the coordinates (<x>, <y>)
        with radius given by <r>. The <color> argument is a 6 digit hex
        representing a color in RGB format.

        Example:

        -> circle 0.5 0.5 1 ff0000
        """

        x, y, r, color = args.split(" ")

        circle = Circle(float(x), float(y), float(r), fill=True)
        self.image.add_layer(circle, FillColor(color))

    def do_square(self, args):
        """square <x> <y> <size> <color>

        This command will draw a square centered as (<x>, <y>) with side
        length given by <size>. The <color> argument is a 6 digit hex color
        representing a color in RGB format.

        Example:

        -> square -0.2 0.4 1.5 00ff00
        """

        x, y, size, color = args.split(" ")

        square = Square(float(x), float(y), float(size))
        self.image.add_layer(square, FillColor(color))

    def default(self, line):
        """This method is called whenever the command doesn't match any of
        the builtin commands or the commands defined above."""

        if line == "q" or line == "EOF":
            return True

        return super().default(line)

    def postcmd(self, stop, line):
        """This method is called after each command has been processed and
        this is where we can add feddback for the user by drawing the image
        they have defined so far.
        """

        if stop:
            return True

        self.update_image()

    def update_image(self):

        # Re-render the image
        self.image(1920, 1080)

        # Update the preview
        self.ax.imshow(self.image.data)
        self.fig.show()


if __name__ == "__main__":
    prompt = StyloPrompt()
    prompt.cmdloop()