pipe 1.6.0

Module enablig a sh like infix syntax (using pipes)

Infix programming toolkit

Module enabling a sh like infix syntax (using pipes).

Introduction

As an example, here is the solution for the 2nd Euler Project exercise:

Find the sum of all the even-valued terms in Fibonacci which do not exceed four million.

Given fib a generator of Fibonacci numbers:

euler2 = (fib() | where(lambda x: x % 2 == 0)
                | take_while(lambda x: x < 4000000)
                | add)

Deprecations of pipe 1.x

In pipe 1.x a lot of functions were returning iterables and a lot other functions were returning non-iterables, causing confusion. The one returning non-iterables could only be used as the last function of a pipe expression, so they are in fact useless:

range(100) | where(lambda x: x % 2 == 0) | add

can be rewritten with no less readability as:

sum(range(100) | where(lambda x: x % 2 == 0))

so all pipes returning a non-pipe are now deprecated and will be removed in pipe 2.0.

Vocabulary

• A Pipe: a Pipe is a 'pipeable' function, something that you can pipe to, In the code '[1, 2, 3] | add' add is a Pipe
• A Pipe function: A standard function returning a Pipe so it can be used like a normal Pipe but called like in : [1, 2, 3] | concat("#")

Syntax

I don't like import * but for the following examples in an REPL it will be OK, so:

>>> from pipe import *

The basic syntax is to use a Pipe like in a shell:

>>> sum(range(100) | select(lambda x: x ** 2) | where(lambda x: x < 100))
285

Some pipes take an argument, some do not need one:

>>> sum([1, 2, 3, 4] | where(lambda x: x % 2 == 0))
6

>>> sum([1, [2, 3], 4] | traverse)
10

A Pipe as a function is nothing more than a function returning a specialized Pipe.

Constructing your own

You can construct your pipes using Pipe class initialized with lambdas like:

stdout = Pipe(lambda x: sys.stdout.write(str(x)))
select = Pipe(lambda iterable, pred: (pred(x) for x in iterable))

Or using decorators:

@Pipe
def stdout(x):
    sys.stdout.write(str(x))

Existing Pipes in this module

tee
    tee outputs to the standard output and yield unchanged items, usefull for
    debugging
    >>> sum([1, 2, 3, 4, 5] | tee)
    1
    2
    3
    4
    5
    15

chain
    Chain a sequence of iterables:
    >>> list([[1, 2], [3, 4], [5]] | chain)
    [1, 2, 3, 4, 5]

    Warning : chain only unfold iterable containing ONLY iterables:
      [1, 2, [3]] | chain
    Gives a TypeError: chain argument #1 must support iteration
    Consider using traverse.

traverse
    Recursively unfold iterables:
    >>> list([[1, 2], [[[3], [[4]]], [5]]] | traverse)
    [1, 2, 3, 4, 5]
    >>> squares = (i * i for i in range(3))
    >>> list([[0, 1, 2], squares] | traverse)
    [0, 1, 2, 0, 1, 4]

map()
    Apply a conversion expression given as parameter
    to each element of the given iterable
    >>> list([1, 2, 3] | map(lambda x: x * x))
    [1, 4, 9]

select()
    An alias for map().
    >>> list([1, 2, 3] | select(lambda x: x * x))
    [1, 4, 9]

where()
    Only yields the matching items of the given iterable:
    >>> list([1, 2, 3] | where(lambda x: x % 2 == 0))
    [2]

take_while()
    Like itertools.takewhile, yields elements of the
    given iterable while the predicat is true:
    >>> list([1, 2, 3, 4] | take_while(lambda x: x < 3))
    [1, 2]

skip_while()
    Like itertools.dropwhile, skips elements of the given iterable
    while the predicat is true, then yields others:
    >>> list([1, 2, 3, 4] | skip_while(lambda x: x < 3))
    [3, 4]

chain_with()
    Like itertools.chain, yields elements of the given iterable,
    then yields elements of its parameters
    >>> list((1, 2, 3) | chain_with([4, 5], [6]))
    [1, 2, 3, 4, 5, 6]

take()
    Yields the given quantity of elemenets from the given iterable, like head
    in shell script.
    >>> list((1, 2, 3, 4, 5) | take(2))
    [1, 2]

tail()
    Yiels the given quantity of the last elements of the given iterable.
    >>> list((1, 2, 3, 4, 5) | tail(3))
    [3, 4, 5]

skip()
    Skips the given quantity of elements from the given iterable, then yields
    >>> list((1, 2, 3, 4, 5) | skip(2))
    [3, 4, 5]

islice()
    Just the itertools.islice
    >>> list((1, 2, 3, 4, 5, 6, 7, 8, 9) | islice(2, 8, 2))
    [3, 5, 7]

izip()
    Just the itertools.izip
    >>> list((1, 2, 3, 4, 5, 6, 7, 8, 9)
    ...  | izip([9, 8, 7, 6, 5, 4, 3, 2, 1]))
    [(1, 9), (2, 8), (3, 7), (4, 6), (5, 5), (6, 4), (7, 3), (8, 2), (9, 1)]

groupby()
    Like itertools.groupby(sorted(iterable, key = keyfunc), keyfunc)
    (1, 2, 3, 4, 5, 6, 7, 8, 9) \
            | groupby(lambda x: x % 2 and "Even" or "Odd")
            | select(lambda x: "%s : %s" % (x[0], (x[1] | concat(', '))))
            | concat(' / ')
    'Even : 1, 3, 5, 7, 9 / Odd : 2, 4, 6, 8'

sort()
    Like Python's built-in "sorted" primitive. Allows cmp (Python 2.x
    only), key, and reverse arguments. By default sorts using the
    identity function as the key.

    >>> ''.join("python" | sort)
    'hnopty'
    >>> list([5, -4, 3, -2, 1] | sort(key=abs))
    [1, -2, 3, -4, 5]

dedup()
    Deduplicate values, using the given key function if provided (or else
    the identity)

    >>> list([1, 1, 2, 2, 3, 3, 1, 2, 3] | dedup)
    [1, 2, 3]
    >>> list([1, 1, 2, 2, 3, 3, 1, 2, 3] | dedup(key=lambda n:n % 2))
    [1, 2]

uniq()
    Like dedup() but only deduplicate consecutive values, using the given
    key function if provided (or else the identity)

    >>> list([1, 1, 2, 2, 3, 3, 1, 2, 3] | uniq)
    [1, 2, 3, 1, 2, 3]
    >>> list([1, 1, 2, 2, 3, 3, 1, 2, 3] | uniq(key=lambda n:n % 2))
    [1, 2, 3, 2, 3]

reverse
    Like Python's built-in "reversed" primitive.
    >>> list([1, 2, 3] | reverse)
    [3, 2, 1]

strip
    Like Python's strip-method for str.
    >>> '  abc   ' | strip
    'abc'
    >>> '.,[abc] ] ' | strip('.,[] ')
    'abc'

rstrip
    Like Python's rstrip-method for str.
    >>> '  abc   ' | rstrip
    '  abc'
    >>> '.,[abc] ] ' | rstrip('.,[] ')
    '.,[abc'

lstrip
    Like Python's lstrip-method for str.
    >>> 'abc   ' | lstrip
    'abc   '
    >>> '.,[abc] ] ' | lstrip('.,[] ')
    'abc] ] '

t
    Like Haskell's operator ":"
    >>> list(0 | t(1) | t(2)) == list(range(3))
    True

permutations()
    Returns all possible permutations
    >>> list('ABC' | permutations(2))
    [('A', 'B'), ('A', 'C'), ('B', 'A'), ('B', 'C'), ('C', 'A'), ('C', 'B')]

    >>> list(range(3) | permutations)
    [(0, 1, 2), (0, 2, 1), (1, 0, 2), (1, 2, 0), (2, 0, 1), (2, 1, 0)]

transpose()
    Transposes the rows and columns of a matrix
    >>> [[1, 2, 3], [4, 5, 6], [7, 8, 9]] | transpose
    [(1, 4, 7), (2, 5, 8), (3, 6, 9)]

Euler project samples

Find the sum of all the multiples of 3 or 5 below 1000.

euler1 = (itertools.count() | select(lambda x: x * 3) | take_while(lambda x: x < 1000) | add) \
       + (itertools.count() | select(lambda x: x * 5) | take_while(lambda x: x < 1000) | add) \
       - (itertools.count() | select(lambda x: x * 15) | take_while(lambda x: x < 1000) | add)
assert euler1 == 233168

Find the sum of all the even-valued terms in Fibonacci which do not exceed four million.

euler2 = fib() | where(lambda x: x % 2 == 0) | take_while(lambda x: x < 4000000) | add
assert euler2 == 4613732

Find the difference between the sum of the squares of the first one hundred natural numbers and the square of the sum.

square = lambda x: x * x
euler6 = square(itertools.count(1) | take(100) | add) - (itertools.count(1) | take(100) | select(square) | add)
assert euler6 == 25164150