rubycodeblocks.py

"""
Emulating Ruby-style code blocks in Python.

This example was demonstrated in the PyCon'10 talk titled "Python Metaprogramming".
"""

import sys
import types

def receive_block(func):
    def wrapped(*args):
        if len(args) == 1:
            block = args[0]
            instance = None
        elif len(args) == 2:
            instance, block = args
        
        # Add block to func's scope
        scope = func.func_globals
        scope.update({'block':block})
        
        # create a new func with the new scope
        new_func = types.FunctionType(func.func_code, scope)
        
        if instance:
            return new_func(instance) # return the method
        else:
            return new_func() # return the function
    return wrapped


# Goal - mimic the following Ruby code
#   [1, 2, 3, 4, 5].each( |x| print x**2, " ")

class Array(list):
    @receive_block
    def each(self):
        for i in self:
            block(i)
a = Array([1,2,3,4,5])
@a.each
def _(x): # this is the anonymous code block
    sys.stdout.write(str(x**2) + " ")