README.md

POOP 💩

Python Object Oriented Programming: Python 3.15, infected by Smalltalk.

In POOP there is no if, no for, no print(). Every literal is an object, and every operation is a message sent to one. True decides for itself, a list walks itself, a string prints itself.

"Hello, World!".print()

POOP runs 73 validators on every program, and each one that refuses tells you what to write instead:

$ poop loop.py
poop: for loops are forbidden — use col.do(block) instead
  1 | for i in range(3):
    | ^

POOP is a playground for exploring message passing without leaving Python, not a production tool. It is not on PyPI and has no releases: clone it and play.

Try it

git clone https://github.com/cassiobotaro/poop.git
cd poop
uv sync
uv run poop examples/basics/fizzbuzz.py

Run uv run poop with no arguments for the REPL. :methods "abc" lists what an object understands, and :explain if says why a construct is gone and what replaces it.

FizzBuzz, the POOP way

range(1, 16).do(
    lambda i: (i % 15 == 0).if_true_if_false(
        lambda: "FizzBuzz".print(),
        lambda: (i % 3 == 0).if_true_if_false(
            lambda: "Fizz".print(),
            lambda: (i % 5 == 0).if_true_if_false(
                lambda: "Buzz".print(),
                lambda: i.print(),
            ),
        ),
    )
)

The range is asked to do something for each number. Each comparison answers a Boolean, and the Boolean picks which block to run.

The ten essentials

Python	POOP
print(x)	x.print()
if cond: … / else:	cond.if_true(lambda: …) / cond.if_true_if_false(lambda: …, lambda: …)
for x in col: …	col.do(lambda x: …)
while cond: …	(lambda: cond).while_true(lambda: …)
len(x)	x.len()
x[i]	x.at(i)
x[a:b]	x.slice(a, b)
not x	x.not_()
x and y / x or y	x.and_(lambda: y) / x.or_(lambda: y)
-x	x.negated()

Learn by example

examples/ goes from hello world to the whole Gang of Four catalogue: Composite in place of isinstance, State in place of if, Null Object in place of None checks.

Where to next

• examples/: every example program, grouped by what it teaches
• MIGRATION.md: the Python → POOP recipe book
• INFECTIONS.md: every ban, rewrite and type, and why each exists
• CONTRIBUTING.md: dev setup and conventions
• Issues: bugs and ideas