default-class

The default_class library in Python

Installation

$ pip install default-class

Usage

default_class.StrAndRepr

The StrAndRepr class gives better __str__ and __repr__ methods:

from default_class import StrAndRepr

class Foo(StrAndRepr):
    def __init__(self, a, b, c):
        self.a = a
        self.b = b
        self.c = c
        
obj = Foo(1, 'a', True)
print(obj)

Output:

Foo(a=1, b='a', c=True)

default_class.Comparisons

from default_class import StrAndRepr, Comparisons

class String(StrAndRepr, Comparisons):
    def __init__(self, s):
        self.s = s
    def __eq__(self, x):
        return self.s == x
    def __lt__(self, x):
        return self.s in x

obj = String('abc')
print(obj <= 'bc') # False
print(obj > 'abcd') # False
print(obj >= 'bc') # True
print(obj != 'abcd') # True

default_class.Numeric

The Numeric class in the default_class library uses arithmatic rules to define magic methods.

See this example:

from default_class import Numeric

class Number(Numeric):
    def __init__(self, n):
        self.n = n
        if isinstance(n, Number):
            self.n = n.n
    def __int__(self):
        return int(self.n)
    def __sub__(self, x):
        return Number(self.n - x)
    def __mul__(self, x):
        return Number(self.n * x)
    def __rtruediv__(self, x):
        return Number(x / self.n)
    def __neg__(self):
        return Number(-self.n)

Here, only 5 magic methods (__int__, __sub__, __mul__, __rtruediv__ and __neg__) have been defined, but the Numeric class fills in 14 others. See below:

num = Number(123)

print(num)
print(num + 5)
print(5 + num)
print(1000 - num)
print(5 * num)
print(num / 5)
print(num // 5)
print(1000 // num)
print(num % 5)
print(1000 % num)
print(divmod(num, 5))
print(divmod(1000, num))
print(+num)

Output:

Number(n=123)
Number(n=128)
Number(n=128)
Number(n=877)
Number(n=615)
Number(n=24.6)
Number(n=24)
Number(n=8)
Number(n=3)
Number(n=16)
(Number(n=24), Number(n=3))
(Number(n=8), Number(n=16))
Number(n=123)
Number(n=-123)

Magic methods filled in

StrAndRepr methods have no dependencies

Method
__str__
__repr__

Comparison methods have two sets of dependencies: either can be used

Method	Option 1	Option 2
__eq__	__ne__	__gt__, __lt__
__ne__	__eq__	__gt__, __lt__
__gt__	__le__	__ge__, __eq__
__ge__	__lt__	__gt__, __eq__
__lt__	__ge__	__le__, __eq__
__le__	__gt__	__lt__, __eq__

Numeric methods have one set of dependencies

Method	Dependencies
__add__	__sub__, __neg__
__radd__	__add__
__sub__	__neg__, __rsub__
__rsub__	__neg__, __sub__
__mul__	__rmul__
__rmul__	__mul__
__truediv__	__rtruediv__
__floordiv__	__int__, __truediv__
__rfloordiv__	__int__, __rtruediv__
__mod__	__sub__, __floordiv__, __mul__
__rmod__	__rsub__, __rfloordiv__, __rmul__
__divmod__	__floordiv__, __mod__
__rdivmod__	__rfloordiv__, __rmod__
__pos__	None
__neg__	__sub__

Warning: if not enough methods are filled in already, this could result in a RecursionError

Note: Numeric inherits from both StrAndRepr and Comparisons