pyrepl-hacks 0.5.0

Hacky extensions and helper functions for the new Python REPL.

pyrepl-hacks 🙀

Hacky extensions and helper functions for the new Python REPL.

import pyrepl_hacks as repl

repl.bind("Alt+M", "move-to-indentation")   # Move to first non-space in current line
repl.bind("Shift+Tab", "dedent")            # Dedent the whole input
repl.bind("Alt+Down", "move-line-down")     # Swap current line with next in block
repl.bind("Alt+Up", "move-line-up")         # Swap current line with previous in block
repl.bind("Shift+Home", "home")             # Move to first character in the input
repl.bind("Shift+End", "end")               # Move to last character in the input
repl.bind("Alt+{", "previous-paragraph")  # Move to previous blank line
repl.bind("Alt+}", "next-paragraph")    # Move to next blank line

# Make Ctrl+N insert a specific list of numbers
repl.bind_to_insert("Ctrl+N", "[2, 1, 3, 4, 7, 11, 18, 29]")


@repl.bind(r"Ctrl+X Ctrl+R", with_event=True)
def subprocess_run(reader, event_name, event):
    """Ctrl+X followed by Ctrl+R will insert a subprocess.run command."""
    reader.insert("import subprocess\n")
    code = 'subprocess.run("", shell=True)'
    reader.insert(code)
    for _ in range(len(code) - code.index('""') - 1):
        repl.commands.left(reader, event_name, event)

⚠️ WARNING: here be dragons 🐉

This library relies on Python implementation details which may change in future Python versions.

This library uses the _pyrepl module (and optionally _colorize). As the _ prefix implies, these modules are not designed for public use.

That means that when you upgrade to a newer Python (for example Python 3.15) this code may break. For that reason, the Python versions this package claims to work with are pinned to only known-to-be-working Python versions.

Installing 💾

This package is meant to be installed in its own directory that will then be added to sys.path within your PYTHONSTARTUP file.

For example, you could install pyrepl-hacks into a ~/.pyhacks directory:

mkdir -p ~/.pyhacks
python -m pip install --upgrade pyrepl-hacks --target ~/.pyhacks

Then you can use it in a ~/.pythonrc file:

def _main():
    from pathlib import Path
    import sys
    sys.path.append(str(Path.home() / ".pyhacks"))
    try:
        import pyrepl_hacks as repl
    except ImportError:
        pass  # We must be on Python 3.12 or earlier
    else:
        repl.bind("Alt+M", "move-to-indentation")
        repl.bind("Shift+Tab", "dedent")
        repl.bind("Alt+Down", "move-line-down")
        repl.bind("Alt+Up", "move-line-up")
        repl.bind("Shift+Home", "home")
        repl.bind("Shift+End", "end")
        repl.bind("Alt+{", "previous-paragraph")
        repl.bind("Alt+}", "next-paragraph")

        repl.bind_to_insert("Ctrl+N", "[2, 1, 3, 4, 7, 11, 18, 29]")

_main()
del _main  # Don't pollute the global namespace in our REPL

And put this something like this in your shell configuration file (~/.bashrc, ~/.zshrc, etc.):

export PYTHONSTARTUP="$HOME/.pythonrc"

This will modify the REPL in every Python environment you start.

See my blog post on pyrepl-hacks for more explanation on PYTHONSTARTUP files and that sys.path.append call above.

Command Registering and Key Binding ⌨️

This library includes features for easily registering and binding new REPL commands.

Binding to existing commands

You can bind a key to an existing command:

import pyrepl_hacks as repl

repl.bind("Shift+Home", "home")

Inserting text with a binding

You can use the bind_to_insert helper to bind a key to insert specific text:

import pyrepl_hacks as repl

repl.bind_to_insert("Ctrl+P", "Python?!")

Registering new commands

Need something fancy that doesn't exist yet?

You can register a new command:

import pyrepl_hacks as repl

@repl.register_command
def exit(reader):
    """Exits Python immediately."""
    import sys
    sys.exit(0)

The register_command decorator will turn the under_score separated name into a kebab-case name by default.

The register_command can optionally accept a command name and, if the command needs access to the event name and event object, a with_event=True argument can be provided:

import pyrepl_hacks as repl

@repl.register_command("delete-line", with_event=True)
def delete_whole_line(reader, event_name, event):
    """Move to beginning of line and delete all text."""
    reader.pos = reader.bol()
    repl.commands.kill_line(reader, event_name, event)

After commands have been registered, they can be used with the bind function to bind them to specific keys:

import pyrepl_hacks as repl

repl.bind("F4", "exit")
repl.bind("Ctrl+X Ctrl+D", "delete-line")

Binding keys while registering

The bind function can also be used as a decorator to register a command and bind it to a specific key combination at the same time:

import pyrepl_hacks as repl

@repl.bind("F4")
def exit(reader):
    """Exits Python immediately."""
    import sys
    sys.exit(0)

Since there's not much point in making a new command without binding it, you'll usually want to use bind instead of register_command.

Just like register_command, bind decorator can also accept a with_event=True argument to pass the event name and event object into the command function.

Available Commands 📑

Here are some of the interesting commands provided by Python (in _pyrepl.commands):

• clear-screen: Clear screen (Ctrl+L)
• previous-history: Show previous block (Ctrl+P)
• next-history: Show next block (Ctrl+N)
• accept: Run current code block (Alt+Enter)
• beginning-of-line: Move cursor to the first character of the current line (Ctrl+A or Home)
• end-of-line: Move cursor to the last character of the current line (Ctrl+E or End)
• home: Move cursor the first character in the code block
• end: Move cursor the last character in the code block
• kill-line: Delete to end of line (Ctrl+K)
• unix-line-discard: Delete to beginning of line (Ctrl+U)
• backward-word: Move cursor back one word (Ctrl+Left)
• forward-word: Move cursor forward one word (Ctrl+Right)
• backward-kill-word: Delete to beginning of word (Alt+Backspace)
• kill-word: Delete to end of word (Alt+D)

See here for which keyboard shortcuts these are bound to by default.

This pyrepl-hacks project provides some additional commands as well:

• move-to-indentation: Move to first non-space in current line
• dedent: Dedent the whole code block
• move-line-down: Swap current line with next one in the block
• move-line-up: Swap current line with previous one in the block
• previous-paragraph: Move to the previous blank line
• next-paragraph: Move to the next blank line

These 6 additional commands have no key bindings by default.

I recommend binding these commands as well as the home and end commands (provided by _pyrepl.commands) which are also unbound by default:

repl.bind("Alt+M", "move-to-indentation")   # Move to first non-space in current line
repl.bind("Shift+Tab", "dedent")            # Dedent the whole input
repl.bind("Alt+Down", "move-line-down")     # Swap current line with next in block
repl.bind("Alt+Up", "move-line-up")         # Swap current line with previous in block
repl.bind("Shift+Home", "home")             # Move to first character in the input
repl.bind("Shift+End", "end")               # Move to last character in the input
repl.bind("Alt+{", "previous-paragraph")    # Move to previous blank line
repl.bind("Alt+}", "next-paragraph")        # Move to next blank line

Note that these custom REPL commands and all existing commands provided by _pyrepl.commands include wrapper functions in the commands submodule. These functions are named the same as their command name, except - must be replaced by _:

from pyrepl_hacks.commands import move_to_indentation, clear_screen

Customizing Your Syntax Theme 🎨

Python 3.14 includes syntax highlighting in the REPL.

You can use the update_theme command from pyrepl-hacks to customize the colors your REPL uses:

try:
    import pyrepl_hacks as repl

    repl.update_theme(
        keyword="green",
        builtin="blue",
        comment="intense blue",
        string="cyan",
        number="cyan",
        definition="blue",
        soft_keyword="bold green",
        op="intense green",
        reset="reset, intense green",
    )
except ImportError:
    pass  # We're on Python 3.13 or below

These are the supported colors:

• black
• blue
• cyan
• green
• grey
• magenta
• red
• white
• yellow

Each supports the modifiers bold, intense, background and intense background.

Also the "color" of reset will reset all modifiers.

The Future is Obsolescence? 🦤

This project came out of the things I learned while hacking on my own REPL shortcuts and customizing my REPL's syntax highlighting.

My hope is that this package will be obsolete one day.

I hope that Python will eventually include an official interface for creating new REPL commands and binding keys to commands.

I also hope that some (or all?) of the 4 new commands this module includes will eventually be included with Python by default.