demo_app.py

#!/usr/bin/env python
"""
Simple example of a full screen application with a vertical split.

This will show a window on the left for user input. When the user types, the
reversed input is shown on the right. Pressing Ctrl-Q will quit the application.
"""
from prompt_toolkit.application import Application
from prompt_toolkit.buffer import Buffer
from prompt_toolkit.key_binding import KeyBindings
from prompt_toolkit.layout.containers import HSplit, VSplit, HSplit, Window, WindowAlign
from prompt_toolkit.layout.controls import BufferControl, FormattedTextControl
from prompt_toolkit.layout.layout import Layout
from prompt_toolkit.layout.dimension import Dimension

# 3. Create the buffers
#    ------------------

left_buffer = Buffer()
right_buffer = Buffer()

# 1. First we create the layout
#    --------------------------

command_window = Window(BufferControl(buffer=left_buffer))
output_window = Window(BufferControl(buffer=right_buffer))


body = HSplit(
    [
        command_window,
        # A vertical line in the middle. We explicitly specify the width, to make
        # sure that the layout engine will not try to divide the whole width by
        # three for all these windows.
        Window(char="-", height=Dimension(min=1, max=1)),
        # Display the Result buffer on the right.
        output_window,
    ]
)

# As a demonstration. Let's add a title bar to the top, displaying "Hello world".

# somewhere, because usually the default key bindings include searching. (Press
# Ctrl-R.) It would be really annoying if the search key bindings are handled,
# but the user doesn't see any feedback. We will add the search toolbar to the
# bottom by using an HSplit.


def get_titlebar_text():
    return [
        ("class:title", " Hello world "),
        ("class:title", " (Press [Ctrl-Q] to quit.)"),
    ]


root_container = HSplit(
    [
        # The titlebar.
        Window(
            height=1,
            content=FormattedTextControl(get_titlebar_text),
            align=WindowAlign.CENTER,
        ),
        # Horizontal separator.
        Window(height=1, char="-", style="class:line"),
        # The 'body', like defined above.
        body,
    ]
)


# 2. Adding key bindings
#   --------------------

# As a demonstration, we will add just a ControlQ key binding to exit the
# application.  Key bindings are registered in a
# `prompt_toolkit.key_bindings.registry.Registry` instance. We use the
# `load_default_key_bindings` utility function to create a registry that
# already contains the default key bindings.

kb = KeyBindings()

# Now add the Ctrl-Q binding. We have to pass `eager=True` here. The reason is
# that there is another key *sequence* that starts with Ctrl-Q as well. Yes, a
# key binding is linked to a sequence of keys, not necessarily one key. So,
# what happens if there is a key binding for the letter 'a' and a key binding
# for 'ab'. When 'a' has been pressed, nothing will happen yet. Because the
# next key could be a 'b', but it could as well be anything else. If it's a 'c'
# for instance, we'll handle the key binding for 'a' and then look for a key
# binding for 'c'. So, when there's a common prefix in a key binding sequence,
# prompt-toolkit will wait calling a handler, until we have enough information.

# Now, There is an Emacs key binding for the [Ctrl-Q Any] sequence by default.
# Pressing Ctrl-Q followed by any other key will do a quoted insert. So to be
# sure that we won't wait for that key binding to match, but instead execute
# Ctrl-Q immediately, we can pass eager=True. (Don't make a habit of adding
# `eager=True` to all key bindings, but do it when it conflicts with another
# existing key binding, and you definitely want to override that behaviour.


@kb.add("c-c", eager=True)
@kb.add("c-q", eager=True)
def _(event):
    """
    Pressing Ctrl-Q or Ctrl-C will exit the user interface.

    Setting a return value means: quit the event loop that drives the user
    interface and return this value from the `Application.run()` call.

    Note that Ctrl-Q does not work on all terminals. Sometimes it requires
    executing `stty -ixon`.
    """
    event.app.exit()


# Now we add an event handler that captures change events to the buffer on the
# left. If the text changes over there, we'll update the buffer on the right.


def default_buffer_changed(_):
    """
    When the buffer on the left changes, update the buffer on
    the right. We just reverse the text.
    """
    right_buffer.text = left_buffer.text[::-1]


left_buffer.on_text_changed += default_buffer_changed


# 3. Creating an `Application` instance
#    ----------------------------------

# This glues everything together.

application = Application(
    layout=Layout(root_container, focused_element=command_window),
    key_bindings=kb,
    # Let's add mouse support!
    mouse_support=True,
    # Using an alternate screen buffer means as much as: "run full screen".
    # It switches the terminal to an alternate screen.
    full_screen=True,
)


# 4. Run the application
#    -------------------


def run():
    # Run the interface. (This runs the event loop until Ctrl-Q is pressed.)
    application.run()


if __name__ == "__main__":
    run()