playing with metaprogramming to create a spreasheet-like DSL. This is an extension of a Coding Dojo performed at Yipit (https://github.com/Yipit/yipit-dojo/tree/master/2018-07-25)

spreadsheet.py

from collections import defaultdict


class BaseCell(object):
    def __init__(self, value):
        self.value = value

    def __add__(self, other):
        if not isinstance(other, Cell):
            other = BaseCell(other)
        return Add(self, other)

    def __sub__(self, other):
        if not isinstance(other, Cell):
            other = BaseCell(other)
        return Sub(self, other)        


class Add(BaseCell):
    def __init__(self, x, y):
        self._x = x
        self._y = y

    @property
    def value(self):
        return self._x.value + self._y.value


class Sub(BaseCell):
    def __init__(self, x, y):
        self._x = x
        self._y = y

    @property
    def value(self):
        return self._x.value - self._y.value


class Cell(BaseCell):
    def __init__(self, value=''):
        self.value = value

    @property
    def value(self):
        value = self._value
        while isinstance(value, BaseCell):
            value = value.value
        return value

    @value.setter
    def value(self, new_value):
        if not isinstance(new_value, BaseCell):
            new_value = BaseCell(new_value)
        self._value = new_value


class Spreadsheet(object):
    def __init__(self):
        self._cells = defaultdict(Cell)

    def set(self, value, axis):
        self._cells[axis].value = value

    def get(self, axis):
        return self.cell(axis).value

    def cell(self, axis):
        return self._cells[axis]

    def evaluate(self, axis):
        value = self.get(axis)
        try:
            return float(value)
        except (TypeError, ValueError):
            return value

spreadsheet2.py

from collections import defaultdict


class BaseCell(object):
    def __init__(self, value):
        self.value = value

    def __add__(self, other):
        if not isinstance(other, Cell):
            other = BaseCell(other)
        return BinOp(self, other, lambda x, y: x.value + y.value)

    def __sub__(self, other):
        if not isinstance(other, Cell):
            other = BaseCell(other)
        return BinOp(self, other, lambda x, y: x.value - y.value)


class BinOp(BaseCell):

    def __init__(self, x, y, calculator):
        self._x = x
        self._y = y
        self._calc = calculator

    @property
    def value(self):
        return self._calc(self._x, self._y)



class Cell(BaseCell):
    def __init__(self, value=''):
        self.value = value

    @property
    def value(self):
        value = self._value
        while isinstance(value, BaseCell):
            value = value.value
        return value

    @value.setter
    def value(self, new_value):
        if not isinstance(new_value, BaseCell):
            new_value = BaseCell(new_value)
        self._value = new_value


class Spreadsheet(object):
    def __init__(self):
        self._cells = defaultdict(Cell)

    def set(self, value, axis):
        self._cells[axis].value = value

    def get(self, axis):
        return self.cell(axis).value

    def cell(self, axis):
        return self._cells[axis]

    def evaluate(self, axis):
        value = self.get(axis)
        try:
            return float(value)
        except (TypeError, ValueError):
            return value

tests.py

from spreadsheet import Cell, Spreadsheet

def test_cell():
    cell = Cell('12')
    assert cell.value == '12'


def test_sheet():
    spreadsheet = Spreadsheet()
    spreadsheet.set('12', 'A1')
    assert spreadsheet.get('A1') == '12'


def test_sheet_with_unset_cel():
    spreadsheet = Spreadsheet()
    assert spreadsheet.get('A1') == ''


def test_sheet_can_evaluate_cell():
    spreadsheet = Spreadsheet()
    spreadsheet.set(12.2, 'A1')
    assert spreadsheet.evaluate('A1') == 12.2


def test_sheet_can_evaluate_strings():
    spreadsheet = Spreadsheet()
    spreadsheet.set('test string', 'A1')
    assert spreadsheet.evaluate('A1') == 'test string'


def test_sheet_can_evaluate_formula_with_addition():
    spreadsheet = Spreadsheet()
    spreadsheet.set(1 + 2, 'A1')
    assert spreadsheet.evaluate('A1') == 3.0


def test_spreadsheet_can_get_cell():
    spreadsheet = Spreadsheet()
    spreadsheet.set('abc', 'A1')
    assert spreadsheet.cell('A1').value == 'abc'


def test_sheet_can_store_evaluate_formulas_with_axis():
    spreadsheet = Spreadsheet()
    spreadsheet.set(1, 'A1')
    spreadsheet.set(spreadsheet.cell("A1") + 2 + 1 - 2, 'A2')
    assert spreadsheet.evaluate('A2') == 2.0
    spreadsheet.set(2, 'A1')
    assert spreadsheet.evaluate('A2') == 3.0
    spreadsheet.set(spreadsheet.cell("A1") + spreadsheet.cell("A2"), 'A3')
    assert spreadsheet.evaluate('A3') == 5