method chaining in python

Question

(not to be confused with itertools.chain)

I was reading the following: http://en.wikipedia.org/wiki/Method_chaining

My question is: what is the best way to implement method chaining in python?

Here is my attempt:

class chain():     def __init__(self, my_object):         self.o = my_object      def __getattr__(self, attr):         x = getattr(self.o, attr)         if hasattr(x, '__call__'):             method = x             return lambda *args: self if method(*args) is None else method(*args)         else:             prop = x             return prop  list_ = chain([1, 2, 3, 0]) print list_.extend([9, 5]).sort().reverse()  """ C:\Python27\python.exe C:/Users/Robert/PycharmProjects/contests/sof.py [9, 5, 3, 2, 1, 0] """ 

One problem is if calling method(*args) modifies self.o but doesn't return None. (then should I return self or return what method(*args) returns).

Does anyone have better ways of implementing chaining? There are probably many ways to do it.

Should I just assume a method always returns None so I may always return self.o ?

Answer 1

There is a very handy Pipe library which may be the answer to your question. For example::

seq = fib() | take_while(lambda x: x < 1000000) \             | where(lambda x: x % 2) \             | select(lambda x: x * x) \             | sum() 

Answer 2

It's possible if you use only pure functions so that methods don't modify self.data directly, but instead return the modified version. You also have to return Chainable instances.

Here's an example using collection pipelining with lists:

import itertools  try:     import builtins except ImportError:     import __builtin__ as builtins   class Chainable(object):     def __init__(self, data, method=None):         self.data = data         self.method = method      def __getattr__(self, name):         try:             method = getattr(self.data, name)         except AttributeError:             try:                 method = getattr(builtins, name)             except AttributeError:                 method = getattr(itertools, name)          return Chainable(self.data, method)      def __call__(self, *args, **kwargs):         try:             return Chainable(list(self.method(self.data, *args, **kwargs)))         except TypeError:             return Chainable(list(self.method(args[0], self.data, **kwargs))) 

Use it like this:

chainable_list = Chainable([3, 1, 2, 0]) (chainable_list     .chain([11,8,6,7,9,4,5])     .sorted()     .reversed()     .ifilter(lambda x: x%2)     .islice(3)     .data) >> [11, 9, 7] 

Note that .chain refers to itertools.chain and not the OP's chain.