classdiff - Python Class Difffer

This is a small library to diff (data) classes or any other objects. It is intended two work one obejcts of the same time or NoneType. Diffing different classes is possible but might result in unexpected result. Different from most existing diff tools that produce data structures that show adds, removes or changes, this tool is intended to use for printing a dataclass and higlight the diff with different color coding, similar to the output of Terraform or Pulumi.

Usage

Just pass your classes to the diff function to get back a representation of the diff.

Given the following two classes:

new = SomeResource(
    name="my-data",
    price=2.3,
    quantity=4,
    dangerous=True,
    other=OtherClass(name="OA"),
    not_changed=OtherClass(name="Same"),
)

old = SomeResource(
    name="my-data",
    price=3.3,
    quantity=4,
    dangerous=False,
    other=OtherClass(name="OB"),
    not_changed=OtherClass(name="Same"),
)

Passing them to classdiff.diff in combinations of (None, new), (old, new) and (old, None) and printing the lines in the returned value, the following will be printed with colored output (green for added, red for removed and yellow for changed). Note that each element in the returned list is of type DiffInfo which implements __repr__ to print with proper prefix and color.

> diff(None, new)
----------------------------------------
+ SomeResource(
+   dangerous = True
+   name = my-data
+   not_changed = OtherClass(
+     name = Same
+   )
+   other = OtherClass(
+     name = OA
+   )
+   price = 2.3
+   quantity = 4
+ )

> diff(old, new)
----------------------------------------
~ SomeResource(
~   dangerous = False => True
    name = my-data
    not_changed = OtherClass(
      name = Same
    )
~   other = OtherClass(
~     name = OB => OA
~   )
~   price = 3.3 => 2.3
    quantity = 4
~ )

> diff(old, None)
----------------------------------------
- SomeResource(
-   dangerous = False
-   name = my-data
-   not_changed = OtherClass(
-     name = Same
-   )
-   other = OtherClass(
-     name = OB
-   )
-   price = 3.3
-   quantity = 4
- )

Development

All code is formatted and analyzed with ruff. Tests are run with pytest.

› poetry run ruff check .
› poetry run ruff format .
› poetry run mypy .
› poetry run pytest tests/