textual-diff-view 0.1.2

Beautiful Diff view widget for Textual applications

Textual Diff View

Textual Diff View is a Textual widget to display beautiful diffs in your terminal application. Originally built for Toad, this widget may be used standalone.

This is what it can look like...

Features

The DiffView widget displays two versions of a file with syntax and changes clearly highlighted. Deleted lines / characters are shown with a red highlight. Added lines / characters are shown with a green highlight.

There are two layout options; a unified view which shows the two files top-to-bottom with highlights, and a split view which shows the two files next to each other.

DiffView can also display annotations ("+" and "-" for added and deleted), to improve readability for color blind users.

Textual's theming system provides a variety of themes for the diff view, both light and dark.

Example

The following is a simple app to display a diff between two files from the command line.

from textual.app import App, ComposeResult
from textual import containers
from textual.reactive import var
from textual import widgets

from textual_diff_view import DiffView, LoadError


class DiffApp(App):
    """Simple app to display a diff between two files."""

    BINDINGS = [
        ("space", "toggle('split')", "Toggle split"),
        ("a", "toggle('annotations')", "Toggle annotations"),
    ]

    split = var(True)
    annotations = var(True)

    def __init__(self, original: str, modified: str) -> None:
        self.original = original
        self.modified = modified
        super().__init__()

    def compose(self) -> ComposeResult:
        yield containers.VerticalScroll(id="diff-container")
        yield widgets.Footer()

    async def on_mount(self) -> None:
        try:
            diff_view = await DiffView.load(self.original, self.modified)
        except LoadError as error:
            self.notify(str(error), title="Failed to load code", severity="error")
        else:
            diff_view.data_bind(DiffApp.split, DiffApp.annotations)
            await self.query_one("#diff-container").mount(diff_view)


if __name__ == "__main__":
    import sys

    if len(sys.argv) != 3:
        print("Usage python tdiff.py PATH1 PATH2\nTry: python tdiff.py")
    else:
        app = DiffApp(sys.argv[1], sys.argv[2])
        app.run()

You can find this file in the examples/ directory. Run it with the following:

uv run python tdiff.py example1.rs example2.rs

Use space to toggle unified / split, and a to toggle annotations.

Screenshots

A few screenshots taken from the example app:

Installing

Texual Diff View is on PyPI and may be installed with pip, or uv.

Here's how to install with uv:

uv add textual-diff-view

How to use

Import the widget with the following:

from textual_diff_view import DiffView

Then yield an instance of DiffView in your compose method.

The constructor accepts 4 positional arguments:

Argument	type	Purpose
path_original	str	A path to the original code
path_modified	str	A path to the modified code
code_original	str	The contents of the original code
code_modified	str	The contents of the modified code

Additionally, the constructor accepts the standard keyword arguments, name, id, and classes——which have the same meaning as Textual's built in widgets.

Here's a very simple example:

from textual.app import App, ComposeResult
from textual import containers

from textual_diff_view import DiffView

HELLO1 = """
def greet():
    print "Hello!"

greet()
"""

HELLO2 = """
def greet(name:str):
    print(f"Hello, {name}!")

greet('Will')
"""


class Hello(App):
    def compose(self) -> ComposeResult:
        with containers.VerticalScroll():
            yield DiffView("hello1.py", "hello2.py", HELLO1, HELLO2)


Hello().run()

Note that we put the DiffView within a VerticalScroll, so the user may scroll the container if the diff doesn't fit.

The above code will generate the following output:

Load constructor

DiffView provides an alternative constructor, DiffView.load, which also loads the code. If both your original code and modified code is on disk, this may be simpler than the standard constructor.

DiffView.load accepts the following positional arguments:

Argument	Type	Purpose
path_original	str or Path	A path to the original code
path_modified	str or Path	A path to the modified code

Since load is a coroutine, you would typically call it from a message handler in another widget, or App, then mount it somewhere in the DOM.

The code would look something like the following:

diff_view = await DiffView.load("original.py", "modified.py")
await self.query_one("VerticalScroll").mount(diff_view)

Reactives

The DiffView supports the following reactive attributes.

Name	Type	Explanation
split	bool	Enables split view when True, or unified view when False
auto_split	bool	Automatically enable split view if there is enough space to fit the longest lines from both file.
annotations	bool	Enable annotations ("+" or "-" symbols). It is reccomended that apps always offer this for color blind users.

Roadmap

There are a few remaining features that I anticipate a need for:

• Word wrapping The widget currently supports horizontal scrolling (via mouse-wheel, trackpad, or shift+mouse-wheel). This works rather well, but has the downside that it is not especially discoverable. An option to enable word wrapping would be useful.
• ANSI theme A future version will add support for ANSI themes, which is limited to the user's choice of 16 colors. It will never look as good, but some people say they prefer it.

There are also a few more high-effort features that I could be tempted to implement:

• Swappable diff methods. There is no perfect diff algorithm. They all have their trade-offs. The DiffView widget uses Python's difflib but it could offer an interface to add other diff algorithms.
• AST level diffs A diff view that works at the AST level can offer diffs that more closely reflect how a human might edit code.

License

DiffView is licensed under the terms of the AGPL license. A commercial license is available if you aren't comfortable with the copyleft restriction. Contact Will McGugan for more information.