# -*- coding: utf-8 -*-
from functools import wraps
import itertools
[docs]class PipeLine(object):
"""
A coroutine wrapper which enables pipelining syntax.
:class:`PipeLine` allows you to flatten once-nested code just by wrapping
your generators. The class provides combinators in the form of operators,
allowing you to plug two generators together without having to nest lots of
function calls. For example::
>>> def summer(stdin):
... sum = 0
... for item in stdin:
... sum += item
... yield sum
>>> pipeline = PipeLine(lambda: iter([1, 2, 3, 4])) | PipeLine(summer)
>>> pipeline
<PipeLine: <lambda> | summer>
>>> for item in pipeline:
... print item
1
3
6
10
The yielded output of each generator in the chain becomes the input for the
next. The rules for writing a pipeline function are simple:
:class:`PipeLine` requires a callable which accepts a single argument (the
input), and returns an iterator. The only exception is the first part of
the pipeline, which should accept no arguments (as there will be no input).
To create pipeline functions, use the :py:decorator:`pipe` decorator::
>>> @pipe
... def my_generator():
... yield 1
... yield 2
... yield 3
>>> pl = my_generator()
>>> pl
<PipeLine: my_generator>
>>> for item in pl:
... print item
1
2
3
If your pipeline accepts input, an iterator will be provided as the first
argument to the function::
>>> @pipe
... def add_one(input):
... for item in input:
... yield item + 1
>>> pl = my_generator() | add_one()
>>> pl
<PipeLine: my_generator | add_one>
>>> for item in pl:
... print item
2
3
4
Even with input, your functions can still accept other parameters::
>>> @pipe
... def adder(input, amount):
... for item in input:
... yield item + amount
>>> pl = my_generator() | adder(3)
>>> pl
<PipeLine: my_generator | adder>
>>> for item in pl:
... print item
4
5
6
Some operators are overridden to provide pipeline combinators (methods
which take multiple pipelines and return a new pipeline). For example,
multiplying two pipelines gets you their cross product::
>>> pl = my_generator() | (adder(3) * adder(6))
>>> pl
<PipeLine: my_generator | adder * adder>
>>> for item in pl:
... print item
(4, 7)
(4, 8)
(4, 9)
(5, 7)
(5, 8)
(5, 9)
(6, 7)
(6, 8)
(6, 9)
Adding two pipelines will chain the same input through both::
>>> pl = my_generator() | (adder(3) + adder(12))
>>> pl
<PipeLine: my_generator | adder + adder>
>>> for item in pl:
... print item
4
5
6
13
14
15
"""
__slots__ = ('coro_func',)
def __init__(self, coro_func):
self.coro_func = coro_func
@property
def __name__(self):
return self.coro_func.__name__
def __repr__(self):
return '<PipeLine: %s>' % getattr(self.coro_func, '__name__', repr(self.coro_func))
def __or__(self, target):
return target.__ror__(self)
def __ror__(self, source):
r"""
Connect two pipes so that one's output becomes the other's input.
A simple example::
>>> from itertools import imap
>>> p = (PipeLine(lambda: iter([1, 2, 3, 4])) |
... PipeLine(lambda stdin: imap(lambda x: x + 3, stdin)))
>>> p
<PipeLine: <lambda> | <lambda>>
>>> list(p)
[4, 5, 6, 7]
"""
def pipe():
return self.coro_func(iter(source))
pipe.__name__ = '%s | %s' % (
getattr(source, '__name__', repr(source)),
getattr(self.coro_func, '__name__', repr(self.coro_func)))
return PipeLine(pipe)
def __mul__(self, other):
"""
Yield the cross product between two alternative pipes.
A simple example::
>>> @pipe
... def echo(values):
... for x in values:
... yield x
>>> list(echo([0, 1]) * echo([9, 10]))
[(0, 9), (0, 10), (1, 9), (1, 10)]
"""
def product(stdin=None):
if stdin is None:
return itertools.product(self, other)
stdin1, stdin2 = itertools.tee(stdin, 2)
return itertools.product((stdin1 | self), (stdin2 | other))
product.__name__ = '%s * %s' % (
getattr(self.coro_func, '__name__', repr(self.coro_func)),
getattr(other, '__name__', repr(other)))
return pipe(product)()
def __add__(self, other):
"""
Yield the chained output of two alternative pipes.
Example::
>>> @pipe
... def echo(values):
... for x in values:
... yield x
>>> list(echo([1, 2, 3]) + echo([4, 5, 6]))
[1, 2, 3, 4, 5, 6]
"""
def concat(stdin=None):
if stdin is None:
return itertools.chain(self, other)
stdin1, stdin2 = itertools.tee(stdin, 2)
return itertools.chain((stdin1 | self), (stdin2 | other))
concat.__name__ = '%s + %s' % (
getattr(self.coro_func, '__name__', repr(self.coro_func)),
getattr(other, '__name__', repr(other)))
return pipe(concat)()
def __iter__(self):
return self.coro_func()
[docs]def pipe(func):
"""
Wrap a function as a pipeline.
>>> @pipe
... def printer(stdin, outfile=None):
... for item in stdin:
... print >>outfile, item
... yield item
>>> @pipe
... def echo(*values):
... for value in values:
... yield value
>>> p = printer()
>>> p
<PipeLine: printer>
>>> p = echo(1, 2, 3) | p
>>> p
<PipeLine: echo | printer>
>>> output = list(p)
1
2
3
>>> output
[1, 2, 3]
"""
@wraps(func)
def wrapper(*args, **kwargs):
@wraps(func)
def coro_func(stdin=None):
if stdin is None:
return func(*args, **kwargs)
return func(stdin, *args, **kwargs)
return PipeLine(coro_func)
return wrapper