Strategies, staticmethods, modules, OH MY

gistfile1.py

# http://en.wikipedia.org/wiki/Strategy_pattern

# class_strategy.py:
#   class IntegerStrategy(object):
#       @staticmethod
#       def add(a, b):
#           ...
#   class FloatStrategy(object):
#       @staticmethod
#       def add(a, b):
#           ...

# module_strategy/integer_strategy.py:
#   def add(a, b):
#       ...

# module_strategy/float_strategy.py:
#   def add(a, b):
#       ...

from class_strategy import IntegerStrategy, FloatStrategy, DecimalFloatStrategy
from module_strategy import integer_strategy, float_strategy, decimal_float_strategy

def f(x, strategy):
    y = strategy.add(x, x)
    
# So do you like:
print f(1, IntegerStrategy)
# Or:
print f(1, integer_strategy)

… but when you're doing this, you almost always want to have some state along with the strategy, and then you're just using a plain old class-with-methods.

For example, maybe you want to include overflow handling:

class IntegerStrategy(object):
    def __init__(self, overflow="warn"):
        self.overflow = overflow
    def add(self, a, b):
        res = a + b
        if res > sys.maxint:
            if self.overflow == "warn":
                warnings.warn("overflow during addition")
        return res

print f(1, IntegerStrategy())