Demystifying python magic __methods__

A walk through of python dunder methods and their usages.

Transcript

1. DEMYSTIFYING PYTHON
   MAGIC __METHODS__
   Naren
   

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2. WHO AM I ?
   Naren
   Software Consultant
   @DudeWhoCode

   

   Cycling | Travelling | Blogging
   

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3. MAGIC METHODS
   • What ?
   • Why ?
   • How ?
   

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4. MOST FAMILIAR MAGIC METHOD ?
   

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5. MOST FAMILIAR MAGIC METHOD ?
   __init__( )
   

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6. WHAT?
   • Pre-defined methods used to enrich your classes
   • Also known as
   • Special methods
   • Dunder methods (Double underscores)
   • Lets you to emulate the builtin types
   

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7. YOU KNOW…
   In [1]: l = ['a', 'b', 'c', ‘d']
   In [2]: l.index('b')
   Out[2]: 1
   In [3]: t = ('a', 'b', 'c', 'd',)
   In [4]: t.index('b')
   Out[4]: 1
   In [5]: len(l)
   Out[5]: 4
   In [6]: len(t)
   Out[6]: 4
   

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8. FROM PYTHON FAQ…
   Why does Python use methods for some functionality (e.g.
   list.index()) but functions for other (e.g. len(list))?
   • The major reason is history.
   • Functions were used for those operations that were generic for a
   group of types and which were intended to work even for objects that
   didn’t have methods at all (e.g. tuples). It is also convenient to have a
   function that can readily be applied to an amorphous collection of
   objects when you use the functional features of Python (map(),
   apply() et al).
   • In fact, implementing len(), max(), min() as a built-in function is
   actually less code than implementing them as methods for each type.
   • It’s too late to make such fundamental changes now. The functions
   have to remain to avoid massive code breakage.
   

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9. HOW ?
   

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10. DEMO
    

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12. __init__
    __new__
    __del__
    __hash__
    __slots__
    __dict__
    __instancecheck__
    __subclasscheck__
    __subclasshook__
    __enter__
    __exit__
    __copy__
    __deepcopy__
    __getstate__
    __reduce__
    __reduce_ex__
    __getnewargs__
    __getattr__
    __getattribute__
    __setattr__
    __delattr__
    __dir__
    __add__
    __sub__
    __mul__
    __floordiv__
    __truediv__
    __mod__
    __pow__
    __lshift__
    __rshift__
    __and__
    __xor__
    __or__
    __iadd__
    __isub__
    __imul__
    __idiv__
    __ifloordiv__
    __imod__
    __ipow__
    __ilshift__
    __irshift__
    __iand__
    __ixor__
    __ior__
    __neg__
    __pos__
    __abs__
    __invert__
    __complex__
    __int__

    

    __long__
    __float__
    __oct__
    __hex__
    __lt__
    __le__
    __eq__
    __ne__
    __ge__
    __gt__
    

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13. BINARY OPERATORS
    + object.__add__(self, other)
    - object.__sub__(self, other)
    * object.__mul__(self, other)
    // object.__floordiv__(self, other)
    / object.__truediv__(self, other)
    % object.__mod__(self, other)
    ** object.__pow__(self,
    other[, modulo])
    << object.__lshift__(self, other)
    

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14. BINARY OPERATORS (CONTD.)
    << object.__lshift__(self, other)
    >> object.__rshift__(self, other)
    & object.__and__(self, other)
    ^ object.__xor__(self, other)
    | object.__or__(self, other)
    

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15. EXTENDED OPERATORS
    += object.__iadd__(self, other)
    -= object.__isub__(self, other)
    *= object.__imul__(self, other)
    /= object.__idiv__(self, other)
    //= object.__ifloordiv__(self, other)
    %= object.__imod__(self, other)
    <<=object.__ilshift__(self, other)
    >>=object.__irshift__(self, other)
    

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16. EXTENDED OPERATORS
    (CONTD.)
    |=object.__ior__(self, other)
    &= object.__iand__(self, other)
    ^= object.__ixor__(self, other)
    **= object.__ipow__(self, other[, modulo])
    

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17. UNARY OPERATORS
    - object.__neg__(self)
    + object.__pos__(self)
    abs() object.__abs__(self)
    ~ object.__invert__(self)
    complex() object.__complex__(self)
    int() object.__int__(self)
    long()object.__long__(self)
    float() object.__float__(self)
    oct() object.__oct__(self)
    hex() object.__hex__(self)
    

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18. COMPARISON OPERATORS
    < object.__lt__(self, other)
    <= object.__le__(self, other)
    == object.__eq__(self, other)
    !=object.__ne__(self, other)
    >= object.__ge__(self, other)
    > object.__gt__(self, other)
    

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19. ⚠ CAUTION ⚠
    • Over use of magic methods makes your code
    complex to understand
    

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20. THANK YOU,
    NAREN
    @DudeWhoCode
    Slides:

    www.dudewho.codes/talks
    

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