Functional pipes in python like %>% from R's magritrr

Question

In R (thanks to magritrr) you can now perform operations with a more functional piping syntax via %>%. This means that instead of coding this: <

Answer 1

There is no need for 3rd party libraries or confusing operator trickery to implement a pipe function - you can get the basics going quite easily yourself.

Lets start by defining what a pipe function actually is. At its heart, it is just a way to express a series of function calls in logical order, rather than the standard 'inside out' order.

For example, lets look at these functions:

def one(value):
  return value

def two(value):
  return 2*value

def three(value):
  return 3*value

Not very interesting, but assume interesting things are happening to value. We want to call them in order, passing the output of each to the next. In vanilla python that would be:

result = three(two(one(1)))

It is not incredibly readable and for more complex pipelines its gonna get worse. So, here is a simple pipe function which takes an initial argument, and the series of functions to apply it to:

def pipe(first, *args):
  for fn in args:
    first = fn(first)
  return first

Lets call it:

result = pipe(1, one, two, three)

That looks like very readable 'pipe' syntax to me :). I don't see how it is any less readable than overloading operators or anything like that. In fact, I would argue that it is more readable python code

Here is the humble pipe solving the OP's examples:

from math import sqrt
from datetime import datetime

def as_date(s):
  return datetime.strptime(s, '%Y-%m-%d')

def as_character(value):
  # Do whatever as.character does
  return value

pipe("2014-01-01", as_date)
pipe(12, sqrt, lambda x: x**2, as_character)