pyrio

PYRIO

Functional-style Streams API library

Facilitates processing of collections and iterables using fluent APIs.
Gives access to files of various types (json, toml, yaml, xml, csv and tsv) for reading and executing complex queries
Provides easy integration with itertools
(NB: Commonly used itertools 'recipes' are included as part of the main APIs)

How to use

Creating streams

• stream from iterable

Stream([1, 2, 3])

• from variadic arguments

Stream.of(1, 2, 3)

• empty stream

Stream.empty()

• infinite ordered stream

Stream.iterate(0, lambda x: x + 1)

• infinite unordered stream

import random

Stream.generate(lambda: random.random())

• infinite stream with given value

Stream.constant(42)

• concat
  (concatenate several streams together or add new streams to the current one)

Stream.concat((1, 2, 3), [5, 6]).to_list()
Stream.of(1, 2, 3).concat([4, 5]).to_list()

• prepend
  (prepend iterable to current stream)

Stream([2, 3, 4]).prepend(0, 1).to_list()

---

Intermediate operations

• filter

Stream([1, 2, 3]).filter(lambda x: x % 2 == 0)

• map

Stream([1, 2, 3]).map(str).to_list()
Stream([1, 2, 3]).map(lambda x: x + 5).to_list()

• filter_map
  (filter out all None or falsy values (if falsy=True) and applies mapper function to the elements of the stream)

Stream.of(None, "foo", "", "bar", 0, []).filter_map(str.upper, falsy=True).to_list()

["FOO", "BAR"]

• flat_map
  (map each element of the stream and yields the elements of the produced iterators)

Stream([[1, 2], [3, 4], [5]]).flat_map(lambda x: Stream(x)).to_list()

[1, 2, 3, 4, 5]

• flatten

Stream([[1, 2], [3, 4], [5]]).flatten().to_list()

[1, 2, 3, 4, 5]

• reduce
  (returns Optional)

Stream([1, 2, 3]).reduce(lambda acc, val: acc + val, identity=3).get()

• peek
  (perform the provided operation on each element of the stream without consuming it)

(Stream([1, 2, 3, 4])
    .filter(lambda x: x > 2)
    .peek(lambda x: print(f"{x} ", end=""))
    .map(lambda x: x * 20)
    .to_list())

• view
  (provides access to a selected part of the stream)

Stream([1, 2, 3, 4, 5, 6, 7, 8, 9]).view(start=1, stop=-3, step=2).to_list()

[2, 4, 6]

• distinct
  (returns a stream with the distinct elements of the current one)

Stream([1, 1, 2, 2, 2, 3]).distinct().to_list()

• skip
  (discards the first n elements of the stream and returns a new stream with the remaining ones)

Stream.iterate(0, lambda x: x + 1).skip(5).limit(5).to_list()

• limit / head
  (returns a stream with the first n elements, or fewer if the underlying iterator ends sooner)

Stream([1, 2, 3, 4, 5, 6, 7, 8, 9, 10]).limit(3).to_tuple()
Stream([1, 2, 3, 4, 5, 6, 7, 8, 9, 10]).head(3).to_tuple()

• tail
  (returns a stream with the last n elements, or fewer if the underlying iterator ends sooner)

Stream([1, 2, 3, 4, 5, 6, 7, 8, 9, 10]).tail(3).to_tuple()

• take_while
  (returns a stream that yields elements based on a predicate)

Stream.of(1, 2, 3, 4, 5, 6, 7, 2, 3).take_while(lambda x: x < 5).to_list()

[1, 2, 3, 4]

• drop_while
  (returns a stream that skips elements based on a predicate and yields the remaining ones)

Stream.of(1, 2, 3, 5, 6, 7, 2).drop_while(lambda x: x < 5).to_list()

[5, 6, 7, 2]

• sorted
  (sorts the elements of the current stream according to natural order or based on the given comparator;
  if 'reverse' flag is True, the elements are sorted in descending order)

(Stream.of((3, 30), (2, 30), (2, 20), (1, 20), (1, 10))
    .sorted(lambda x: (x[0], x[1]), reverse=True)
    .to_list())

[(3, 30), (2, 30), (2, 20), (1, 20), (1, 10)]

---

Terminal operations

Collectors

• collecting result into list, tuple, set

Stream([1, 2, 3]).to_list()
Stream([1, 2, 3]).to_tuple()
Stream([1, 2, 3]).to_set()

• into dict

class Foo:
    def __init__(self, name, num):
        self.name = name
        self.num = num
        
Stream([Foo("fizz", 1), Foo("buzz", 2)]).to_dict(lambda x: (x.name, x.num))

{"fizz": 1, "buzz": 2}

In the case of a collision (duplicate keys) the 'merger' functions indicates which entry should be kept

collection = [Foo("fizz", 1), Foo("fizz", 2), Foo("buzz", 2)]
Stream(collection).to_dict(collector=lambda x: (x.name, x.num), merger=lambda old, new: old)

{"fizz": 1, "buzz": 2}

• alternative for working with collectors is using the collect method

Stream([1, 2, 3]).collect(tuple)
Stream.of(1, 2, 3).collect(list)
Stream.of(1, 1, 2, 2, 2, 3).collect(set)
Stream.of(1, 2, 3, 4).collect(dict, lambda x: (str(x), x * 10))

• grouping

Stream("AAAABBBCCD").group_by(collector=lambda key, grouper: (key, len(grouper)))

{"A": 4, "B": 3, "C": 2, "D": 1}

coll = [Foo("fizz", 1), Foo("fizz", 2), Foo("fizz", 3), Foo("buzz", 2), Foo("buzz", 3), Foo("buzz", 4), Foo("buzz", 5)]
Stream(coll).group_by(
    classifier=lambda obj: obj.name,
    collector=lambda key, grouper: (key, [(obj.name, obj.num) for obj in list(grouper)]))

{
  "fizz": [("fizz", 1), ("fizz", 2), ("fizz", 3)],
  "buzz": [("buzz", 2), ("buzz", 3), ("buzz", 4), ("buzz", 5)],
}

Other terminal operations

• for_each

Stream([1, 2, 3, 4]).for_each(lambda x: print(f"{'#' * x} ", end=""))

• count
  (returns the count of elements in the stream)

Stream([1, 2, 3, 4]).filter(lambda x: x % 2 == 0).count()

• sum

Stream.of(1, 2, 3, 4).sum() 

• find_first
  (search for an element of the stream that satisfies a predicate, returns an Optional with the first found value, if any, or None)

Stream.of(1, 2, 3, 4).filter(lambda x: x % 2 == 0).find_first().get()

• find_any
  (search for an element of the stream that satisfies a predicate, returns an Optional with some of the found values, if any, or None)

Stream.of(1, 2, 3, 4).filter(lambda x: x % 2 == 0).find_any().get()

• any_match
  (returns whether any elements of the stream match the given predicate)

Stream.of(1, 2, 3, 4).any_match(lambda x: x > 2)

• all_match
  (returns whether all elements of the stream match the given predicate)

Stream.of(1, 2, 3, 4).all_match(lambda x: x > 2)

• none_match
  (returns whether no elements of the stream match the given predicate)

Stream.of(1, 2, 3, 4).none_match(lambda x: x < 0)

• min
  (returns Optional with the minimum element of the stream)

Stream.of(2, 1, 3, 4).min().get()

• max
  (returns Optional with the maximum element of the stream)

Stream.of(2, 1, 3, 4).max().get()

• compare_with
  (compares linearly the contents of two streams based on a given comparator)

fizz = Foo("fizz", 1)
buzz = Foo("buzz", 2)
Stream([buzz, fizz]).compare_with(Stream([fizz, buzz]), lambda x, y: x.num == y.num)

• quantify
  (count how many of the elements are Truthy or evaluate to True based on a given predicate)

Stream([2, 3, 4, 5, 6]).quantify(predicate=lambda x: x % 2 == 0)

---

Itertools integration

Invoke use method by passing the itertools function and it's arguments as **kwargs

import itertools
import operator

Stream([1, 2, 3, 4, 5, 6, 7, 8, 9, 10]).use(itertools.islice, start=3, stop=8)
Stream.of(1, 2, 3, 4, 5).use(itertools.accumulate, func=operator.mul).to_list()
Stream(range(3)).use(itertools.permutations, r=3).to_list()

Itertools 'recipes'

Invoke the 'recipes' described here as stream methods and pass required key-word arguments

Stream([1, 2, 3]).ncycles(count=2).to_list()
Stream.of(2, 3, 4).take_nth(10, default=66).get()
Stream(["ABC", "D", "EF"]).round_robin().to_list()

---

Querying files with FileStream

• working with json, toml, yaml, xml files

FileStream("path/to/file").map(lambda x: f"{x.key}=>{x.value}").to_tuple()

(
  "abc=>xyz", 
  "qwerty=>42",
)

from operator import itemgetter

(FileStream("path/to/file")
    .filter(lambda x: "a" in x.key)
    .map(lambda x: (x.key, sum(x.value) * 10))
    .sorted(itemgetter(1), reverse=True)
    .map(lambda x: f"{str(x[1])}::{x[0]}")
    .to_list()) 

["230::xza", "110::abba", "30::a"]

FileStream reads data as series of Item objects with key/value attributes.

• querying csv and tsv files
  (each row is read as a dict with keys taken from the header row)

FileStream("path/to/file").map(lambda x: f"fizz: {x['fizz']}, buzz: {x['buzz']}").to_tuple() 

(
  "fizz: 42, buzz: 45",
  "fizz: aaa, buzz: bbb",
)

from operator import itemgetter

FileStream("path/to/file").map(itemgetter('fizz', 'buzz')).to_tuple()

(('42', '45'), ('aaa', 'bbb'))