PyFunctional makes creating data pipelines easy by using chained functional operators. Here are a few examples of what it can do:

• Chained operators: seq(1, 2, 3).map(lambda x: x * 2).reduce(lambda x, y: x + y)
• Expressive and feature complete API
• Read and write text, csv, json, jsonl, sqlite, gzip, bz2, and lzma/xz files
• Parallelize "embarrassingly parallel" operations like map easily
• Complete documentation, rigorous unit test suite, 100% test coverage, and CI which provide robustness

PyFunctional's API takes inspiration from Scala collections, Apache Spark RDDs, and Microsoft LINQ.

1. Installation
2. Examples
   1. Simple Example
   2. Aggregates and Joins
   3. Reading and Writing SQLite3
   4. Data Interchange with Pandas
3. Writing to Files
4. Parallel Execution
5. Github Shortform Documentation
   1. Streams, Transformations, and Actions
   2. Streams API
   3. Transformations and Actions APIs
   4. Lazy Execution
6. Contributing and Bug Fixes
7. Changelog

PyFunctional is available on pypi and can be installed by running:

# Install from command line
$ pip install pyfunctional

Then in python run: from functional import seq

PyFunctional is useful for many tasks, and can natively open several common file types. Here are a few examples of what you can do.

from functional import seq

seq(1, 2, 3, 4)\
    .map(lambda x: x * 2)\
    .filter(lambda x: x > 4)\
    .reduce(lambda x, y: x + y)
# 14

# or if you don't like backslash continuation
(seq(1, 2, 3, 4)
    .map(lambda x: x * 2)
    .filter(lambda x: x > 4)
    .reduce(lambda x, y: x + y)
)
# 14

PyFunctional has three types of functions:

1. Streams: read data for use by the collections API.
2. Transformations: transform data from streams with functions such as map, flat_map, and filter
3. Actions: These cause a series of transformations to evaluate to a concrete value. to_list, reduce, and to_dict are examples of actions.

In the expression seq(1, 2, 3).map(lambda x: x * 2).reduce(lambda x, y: x + y), seq is the stream, map is the transformation, and reduce is the action.

from functional import seq
from collections import namedtuple

Transaction = namedtuple('Transaction', 'reason amount')
transactions = [
    Transaction('github', 7),
    Transaction('food', 10),
    Transaction('coffee', 5),
    Transaction('digitalocean', 5),
    Transaction('food', 5),
    Transaction('riotgames', 25),
    Transaction('food', 10),
    Transaction('amazon', 200),
    Transaction('paycheck', -1000)
]

# Using the Scala/Spark inspired APIs
food_cost = seq(transactions)\
    .filter(lambda x: x.reason == 'food')\
    .map(lambda x: x.amount).sum()

# Using the LINQ inspired APIs
food_cost = seq(transactions)\
    .where(lambda x: x.reason == 'food')\
    .select(lambda x: x.amount).sum()

# Using PyFunctional with fn
from fn import _
food_cost = seq(transactions).filter(_.reason == 'food').map(_.amount).sum()

The account transactions example could be done easily in pure python using list comprehensions. To show some of the things PyFunctional excels at, take a look at a couple of word count examples.

words = 'I dont want to believe I want to know'.split(' ')
seq(words).map(lambda word: (word, 1)).reduce_by_key(lambda x, y: x + y)
# [('dont', 1), ('I', 2), ('to', 2), ('know', 1), ('want', 2), ('believe', 1)]

In the next example we have chat logs formatted in json lines (jsonl) which contain messages and metadata. A typical jsonl file will have one valid json on each line of a file. Below are a few lines out of examples/chat_logs.jsonl.

{"message":"hello anyone there?","date":"10/09","user":"bob"}
{"message":"need some help with a program","date":"10/09","user":"bob"}
{"message":"sure thing. What do you need help with?","date":"10/09","user":"dave"}

from operator import add
import re
messages = seq.jsonl('examples/chat_logs.jsonl')

# Split words on space and normalize before doing word count
def extract_words(message):
    return re.sub('[^0-9a-z ]+', '', message.lower()).split(' ')


word_counts = messages\
    .map(lambda log: extract_words(log['message']))\
    .flatten().map(lambda word: (word, 1))\
    .reduce_by_key(add).order_by(lambda x: x[1])

Next, lets continue that example but introduce a json database of users from examples/users.json. In the previous example we showed how PyFunctional can do word counts, in the next example lets show how PyFunctional can join different data sources.

# First read the json file
users = seq.json('examples/users.json')
#[('sarah',{'date_created':'08/08','news_email':True,'email':'sarah@gmail.com'}),...]

email_domains = users.map(lambda u: u[1]['email'].split('@')[1]).distinct()
# ['yahoo.com', 'python.org', 'gmail.com']

# Join users with their messages
message_tuples = messages.group_by(lambda m: m['user'])
data = users.inner_join(message_tuples)
# [('sarah',
#    (
#      {'date_created':'08/08','news_email':True,'email':'sarah@gmail.com'},
#      [{'date':'10/10','message':'what is a...','user':'sarah'}...]
#    )
#  ),...]

# From here you can imagine doing more complex analysis

In examples/camping_purchases.csv there are a list of camping purchases. Lets do some cost analysis and compare it the required camping gear list stored in examples/gear_list.txt.

purchases = seq.csv('examples/camping_purchases.csv')
total_cost = purchases.select(lambda row: int(row[2])).sum()
# 1275

most_expensive_item = purchases.max_by(lambda row: int(row[2]))
# ['4', 'sleeping bag', ' 350']

purchased_list = purchases.select(lambda row: row[1])
gear_list = seq.open('examples/gear_list.txt').map(lambda row: row.strip())
missing_gear = gear_list.difference(purchased_list)
# ['water bottle','gas','toilet paper','lighter','spoons','sleeping pad',...]

In addition to the aggregate functions shown above (sum and max_by) there are many more. Similarly, there are several more set like functions in addition to difference.

PyFunctional can read and write to SQLite3 database files. In the example below, users are read from examples/users.db which stores them as rows with columns id:Int and name:String.

db_path = 'examples/users.db'
users = seq.sqlite3(db_path, 'select * from user').to_list()
# [(1, 'Tom'), (2, 'Jack'), (3, 'Jane'), (4, 'Stephan')]]

sorted_users = seq.sqlite3(db_path, 'select * from user order by name').to_list()
# [(2, 'Jack'), (3, 'Jane'), (4, 'Stephan'), (1, 'Tom')]

Writing to a SQLite3 database is similarly easy

import sqlite3
from collections import namedtuple

with sqlite3.connect(':memory:') as conn:
    conn.execute('CREATE TABLE user (id INT, name TEXT)')
    conn.commit()
    User = namedtuple('User', 'id name')

    # Write using a specific query
    seq([(1, 'pedro'), (2, 'fritz')]).to_sqlite3(conn, 'INSERT INTO user (id, name) VALUES (?, ?)')

    # Write by inserting values positionally from a tuple/list into named table
    seq([(3, 'sam'), (4, 'stan')]).to_sqlite3(conn, 'user')

    # Write by inferring schema from namedtuple
    seq([User(name='tom', id=5), User(name='keiga', id=6)]).to_sqlite3(conn, 'user')

    # Write by inferring schema from dict
    seq([dict(name='david', id=7), dict(name='jordan', id=8)]).to_sqlite3(conn, 'user')

    # Read everything back to make sure it wrote correctly
    print(list(conn.execute('SELECT * FROM user')))

    # [(1, 'pedro'), (2, 'fritz'), (3, 'sam'), (4, 'stan'), (5, 'tom'), (6, 'keiga'), (7, 'david'), (8, 'jordan')]

Just as PyFunctional can read from csv, json, jsonl, sqlite3, and text files, it can also write them. For complete API documentation see the collections API table or the official docs.

PyFunctional will auto-detect files compressed with gzip, lzma/xz, and bz2. This is done by examining the first several bytes of the file to determine if it is compressed so therefore requires no code changes to work.

To write compressed files, every to_ function has a parameter compression which can be set to the default None for no compression, gzip or gz for gzip compression, lzma or xz for lzma compression, and bz2 for bz2 compression.

The only change required to enable parallelism is to import from functional import pseq instead of from functional import seq and use pseq where you would use seq. The following operations are run in parallel with more to be implemented in a future release:

• map/select
• filter/filter_not/where
• flat_map

Parallelization uses python multiprocessing and squashes chains of embarrassingly parallel operations to reduce overhead costs. For example, a sequence of maps and filters would be executed all at once rather than in multiple loops using multiprocessing

Shortform documentation is below and full documentation is at docs.pyfunctional.pedro.ai.

All of PyFunctional streams can be accessed through the seq object. The primary way to create a stream is by calling seq with an iterable. The seq callable is smart and is able to accept multiple types of parameters as shown in the examples below.

# Passing a list
seq([1, 1, 2, 3]).to_set()
# [1, 2, 3]

# Passing direct arguments
seq(1, 1, 2, 3).map(lambda x: x).to_list()
# [1, 1, 2, 3]

# Passing a single value
seq(1).map(lambda x: -x).to_list()
# [-1]

seq also provides entry to other streams as attribute functions as shown below.

# number range
seq.range(10)

# text file
seq.open('filepath')

# json file
seq.json('filepath')

# jsonl file
seq.jsonl('filepath')

# csv file
seq.csv('filepath')
seq.csv_dict_reader('filepath')

# sqlite3 db and sql query
seq.sqlite3('filepath', 'select * from data')

For more information on the parameters that these functions can take, reference the streams documentation

Below is the complete list of functions which can be called on a stream object from seq. For complete documentation reference transformation and actions API.

Whenever possible, PyFunctional will compute lazily. This is accomplished by tracking the list of transformations that have been applied to the sequence and only evaluating them when an action is called. In PyFunctional this is called tracking lineage. This is also responsible for the ability for PyFunctional to cache results of computation to prevent expensive re-computation. This is predominantly done to preserve sensible behavior and used sparingly. For example, calling size() will cache the underlying sequence. If this was not done and the input was an iterator, then further calls would operate on an expired iterator since it was used to compute the length. Similarly, repr also caches since it is most often used during interactive sessions where its undesirable to keep recomputing the same value. Below are some examples of inspecting lineage.

def times_2(x):
    return 2 * x

elements = (
   seq(1, 1, 2, 3, 4)
      .map(times_2)
      .peek(print)
      .distinct()
)

elements._lineage
# Lineage: sequence -> map(times_2) -> peek(print) -> distinct

l_elements = elements.to_list()
# Prints: 1
# Prints: 1
# Prints: 2
# Prints: 3
# Prints: 4

elements._lineage
# Lineage: sequence -> map(times_2) -> peek(print) -> distinct -> cache

l_elements = elements.to_list()
# The cached result is returned so times_2 is not called and nothing is printed

Files are given special treatment if opened through the seq.open and related APIs. functional.util.ReusableFile implements a wrapper around the standard python file to support multiple iteration over a single file object while correctly handling iteration termination and file closing.

Even though functions like first() are supposed to return a single element, if the element is an iterable, then it is wrapped into a Sequence. For instance:

>>> s = seq(list(), list())
>>> type(s.first())
<class 'functional.pipeline.Sequence'>

That behaviour can be changed with no_wrap option:

>>> type(s.first(no_wrap=True))
<class 'list'>

The option is also accpeted by seq()/pseq() as well as Sequence() constructor, for example:

>>> type(seq([list(), list()], no_wrap=True).last())
<class 'list'>

• SQL based query planner and interpreter
• _ lambda operator

Any contributions or bug reports are welcome. Thus far, there is a 100% acceptance rate for pull requests and contributors have offered valuable feedback and critique on code. It is great to hear from users of the package, especially what it is used for, what works well, and what could be improved.

To contribute, create a fork of PyFunctional, make your changes, then make sure that they pass. In order to be merged, all pull requests must:

• Pass all the unit tests
• Pass all the pylint tests, or ignore warnings with explanation of why its correct to do so
• Not significantly reduce coverage without a good reason (coveralls.io)
• Edit the CHANGELOG.md file in the Next Release heading with changes

Gitter for chat

• PyFunctional 1.5 is tested against Python 3.8 to 3.11 and PyPy3
• PyFunctional 1.4 supports and is tested against Python 3.6, Python 3.7, and PyPy3
• PyFunctional 1.4 and above do not support python 2.7
• PyFunctional 1.4 works in Python 3.5, but is not tested against it
• PyFunctional 1.4 and above partially works in 3.8, parallel processing currently has issues, but other feature work fine
• PyFunctional 1.3 and below supports and was tested against Python 2.7, Python 3.5, Python 3.6, PyPy2, and PyPy3

Changelog

To learn more about me (the author) visit my webpage at pedro.ai.

I created PyFunctional while using Python extensively, and finding that I missed the ease of use for manipulating data that Spark RDDs and Scala collections have. The project takes the best ideas from these APIs as well as LINQ to provide an easy way to manipulate data when using Scala is not an option or PySpark is overkill.

These people have generously contributed their time to improving PyFunctional

• versae
• adrian17
• lucidfrontier45
• Digenis
• ChuyuHsu
• jsemric