python functools partial

partial

1. demo

        >>> from functools import partial
        >>> basetwo = partial(int, base=2)
        >>> basetwo.__doc__ = 'convert base 2 string to an int'
        >>> basetwo('10010')
        18
   

demo

1. make new version of a function with one or more arguments already filled in

2. new version of a function documents itself

3. demo exponentiation

   1. power

       def power(base, exponent):
           return base ** exponent
      

   2. square

       def square(base):
           return power(base, 2)
      

   3. cube

       def cube(base):
           return power(base, 3)
      

   4. use partial

       from functools import partial
      
       square = partial(power, exponent=2)
       cube = partial(power, exponent=3)
      
       def test_partial():
           assert square(2) == 4
           assert cube(2) == 8
      
       def test_partial_docs():
           assert square.keywords == {'exponent': 2}
           assert square.func == power
      
       def test_power_partials():
           power_partials = []
           for x in range(1, 11):
               f = partial(power, exponent=x)
               power_partials.append(f)
           # use list comprehension instead of loop
           [partial(power, exponent=x) for x in range(1, 11)]
      
           assert power_partials[0][2] == 2
           assert power_partials[4][2] == 32
           assert power_partials[9][2] == 1024