pipechain 0.1.1

Functional pipelines in Python using method chaining

PipeChain

Motivation

PipeChain is a utility library for creating functional pipelines. Let's start with a motivating example. We have a list of Australian phone numbers from our users. We need to clean this data before we insert it into the database. With PipeChain, you can do this whole process in one neat pipeline:

from pipechain import PipeChain, PLACEHOLDER as _

nums = [
    "493225813",
    "0491 570 156",
    "55505488",
    "Barry",
    "02 5550 7491",
    "491570156",
    "",
    "1800 975 707"
]

PipeChain(
    nums
).pipe(
    # Remove spaces
    map, lambda x: x.replace(" ", ""), _
).pipe(
    # Remove non-numeric entries
    filter, lambda x: x.isnumeric(), _
).pipe(
    # Add the mobile code to the start of 8-digit numbers
    map, lambda x: "04" + x if len(x) == 8 else x, _
).pipe(
    # Add the 0 to the start of 9-digit numbers
    map, lambda x: "0" + x if len(x) == 9 else x, _
).pipe(
    # Convert to a set to remove duplicates
    set
).eval()

{'0255507491', '0455505488', '0491570156', '0493225813', '1800975707'}

Without PipeChain, we would have to horrifically nest our code, or else use a lot of temporary variables:

set(
    map(
        lambda x: "0" + x if len(x) == 9 else x,
        map(
            lambda x: "04" + x if len(x) == 8 else x,
            filter(
                lambda x: x.isnumeric(),
                map(
                    lambda x: x.replace(" ", ""),
                    nums
                )
            )
        )
    )
)

{'0255507491', '0455505488', '0491570156', '0493225813', '1800975707'}

Installation

pip install pipechain

Usage

Basic Usage

PipeChain has only two exports: PipeChain, and PLACEHOLDER.

PipeChain is a class that defines a pipeline. You create an instance of the class, and then call .pipe() to add another function onto the pipeline:

from pipechain import PipeChain, PLACEHOLDER
PipeChain(1).pipe(str)

PipeChain(arg=1, pipes=[functools.partial(<class 'str'>)])

Finally, you call .eval() to run the pipeline and return the result:

PipeChain(1).pipe(str).eval()

'1'

You can "feed" the pipe at either end, either during construction (PipeChain("foo")), or during evaluation .eval("foo"):

PipeChain().pipe(str).eval(1)

'1'

Each call to .pipe() takes a function, and any additional arguments you provide, both positional and keyword, will be forwarded to the function:

PipeChain(["b", "a", "c"]).pipe(sorted, reverse=True).eval()

['c', 'b', 'a']

Argument Position

By default, the previous value is passed as the first positional argument to the function:

PipeChain(2).pipe(pow, 3).eval()

8

The only magic here is that if you use the PLACEHOLDER variable as an argument to .pipe(), then the pipeline will replace it with the output of the previous pipe at runtime:

PipeChain(2).pipe(pow, 3, PLACEHOLDER).eval()

9

Note that you can rename PLACEHOLDER to something more usable using Python's import statement, e.g.

from pipechain import PLACEHOLDER as _
PipeChain(2).pipe(pow, 3, _).eval()

9

Methods

It might not see like methods will play that well with this pipe convention, but after all, they are just functions. You should be able to access any object's method as a function by accessing it on that object's parent class. In the below example, str is the parent class of "":

"".join(["a", "b", "c"])

'abc'

PipeChain(["a", "b", "c"]).pipe(str.join, "", _).eval()

'abc'

Operators

The same goes for operators, such as +, *, [] etc. We just have to use the operator module in the standard library:

from operator import add, mul, getitem

PipeChain(5).pipe(mul, 3).eval()

15

PipeChain(5).pipe(add, 3).eval()

8

PipeChain(["a", "b", "c"]).pipe(getitem, 1).eval()

'b'

Test Suite

Note, you will need poetry installed.

To run the test suite, use:

git clone https://github.com/multimeric/PipeChain.git
cd PipeChain
poetry install
poetry run pytest test/test.py