datafun 0.4.1

datafun brings the fun back to data pipelines

🍻 datafun

The datafun allows for loading existing datasets or files with different formats and treat them as streaming pipelines. It also allows one to add operations like filter and map in a functional way executed lazily while loading data.

• Overview
• Architecture
• Install
• Usage
• Available datasets
• Custom Datasets

Overview

With datafun you can:

• Load files locally from specific file formats, eg. CSV, JSON etc.
• Load files from remote sources, eg. a CSV or a JSON from a Google Cloud Storage bucket.
• Apply streaming transformations on the fly by applying functional operations (filter, map...) to it.
• Define data transformations to be stored and later used and extended by anyone. This will contribute to an internal hub of common datasets and pipelines used many times.

Architecture

A datafun Dataset is both a lazy stream of data and lazy sequential pipeline of operations.

• It is a stream of data: when you iterate over the dataset, one element at a time is generated and returned to the caller.
• It is a lazy sequential pipeline: every time an element needs to be returned, the pipeline of operations is executed on the current element.

Node types. The DatasetSource class is the first node of the pipeline and is responsible for loading the data from a local or remote storage, then passing it to the next node in the pipeline. DatasetNode objects representing filter or map operations can be added to the pipeline.

Communication. The pipeline communicates in a message-passing fashion. Stream objects are passed between nodes, representing the state of the stream and containing the current element. A stream may be a StartOfStream, EndOfStream, PullStream, or just Stream (when containing data). To give an example of the communication, consider the following pipeline:

TextDataSource -> Map (lambda x: x.lower()) -> Filter (lambda x: "messiah" in x))

and the following stream of data:

"Dune" -> "Dune Messiah" -> "Children of Dune" -> ...

This is what happens when you begin iterating over the stream:

• StartOfStream triggers TextDataSource, which reads the first element Dune
• Stream is forwarded to Map, which transforms Dune into dune
• Stream is forwarded to Filter, the lambda inside fails the check, so a PullStream is sent backward
• PullStream arrives to Map, which sends it back to TextDataSource
• TextDataSource reads the PullStream, generates another element, Dune Messiah, then issues a Stream forward.
• ...
• This Stream arrives at the end, so messiah it is returned to the caller.
• ...

Available transformation operations.

name	Arguments	Description
filter	f: Callable[T, bool]	Filters elements according to f.
map	f: Callable[T, S]	Maps every element to another with function f.
flat_map	f: Callable[T, Iterable[S]] = lambda x: x	A Flat Map takes a list and returns every element, one at a time. The given function f, given element of time T, must return an Iterable of type S. If not provided, f is the identity.
sampling	p: float, seed: int	Samples elements according to the sampling ratio p: 0. < p <= 1.
unique	by: Callable[T, U]	Removes duplicates. by argument specifies a function that extracts the desired information
aggregate	init: Callable[[], S] agg: Callable[[T, S], S] reduce: Callable[[S], R]	Aggregates stream using function f. Hint: given initial value init of type S for aggregated stream, maps f to stream (value: T, aggregated: S) where value is an element of the stream, and aggregated is the current aggregate value. reduce is applied to the aggregated value, if provided
zip	*iterables	Zips elements from multiple dataset, like python zip()
join	other: Dataset, key: Callable, key_left: Callable, key_right: Callable	Joins two datasets based on provided key functions that specify the path in the dictionary. Either specify key for both, or key_left and key_right.
limit	n: int	Limits the number of elements in the streams to the first n
cache		Caches result of previous nodes into memory. Useful when the pipeline is executed multiple times. Be careful with memory intensive operations.

Datasets overloads basic python operations: +, -, *, /.

You can see examples for every operation in the dedicated notebook.

Available info operations.

name	Arguments	Description
info	/	Prints dataset description
summary	/	Prints list of transformations in the pipeline
schema	/	Prints schema of dataset. Useful for csv, json, jsonl

Available output operations.

name	Arguments	Return type	Description
show	n: int	str	Print first n elements as string
take	n: int	List[T]	Returns the first n elements of the dataset
take_while	f: Callable[..., bool]	List[T]	Returns all elements satisfying f
collect	/	List[T]	Returns a list containing all elements. Also prints progress while collecting.

Install

pip install datafun

Usage

import datafun as dfn

Load a raw dataset (local|remote)

ds: Dataset = dfn.load('text', path="path/to/dune_frank_herbert.txt")

for el in ds:
    # do something with el

Load a dataset from iterable data structure

ds = dfn.load(range(N))

ds.take(5) # take first 5 integers
>> [0, 1, 2, 3, 4]

Adding ops to the pipeline, evaluated lazily when generating data

ds = dfn.load('json', path="path/to/file.json")

ds2 = ds.filter(lambda x: x['KEY'] > 10)
ds2 = ds2.map(lambda x: x**2)

print(ds2.summary()) # Shows pipeline ops

for el in ds2:
    # do something with el.
    # This will execute the defined ops one element at a time

Easy streaming transformation of remote dataset!

# Streaming normalize on the fly
ds = (
    dfn
    .load('gcs-jsonl', path='gs://my_bucket/timeseries.jsonl')
    .map(lambda x: x['value'])
)
mean = 3.14 # let's assume to have a mean
norm_ds = ds - mean
for value in norm_ds:
    print(value)

You can see examples for every operation in the dedicated notebook.

Available datasets

ID	Class	Elem. type	Description
text	TextDataset	str	Streams the local text file(s) one line at a time. Glob supported
csv	CSVDataset	dict	Streams the local CSV file(s) one row at a time. Glob supported
json	JSONDataset	dict	Streams the local JSON file(s) one at a time. Glob supported
jsonl	JSONLinesDataset	dict	Streams the local JSONLines file(s) one line at a time. Glob supported
gcs	GCSDataset	str	Download files from Google Cloud Storage, then streams paths to be loaded locally. Glob supported
gcs-text	GCSTextDataset	str	As gcs, but also opens the text file(s) and streams one line a time. Glob supported
gcs-csv	GCSCSVDataset	dict	As gcs, but also opens the CSV file(s) and streams one row a time. Glob supported
gcs-json	GCSJSONDataset	dict	As gcs, but also opens the JSON file(s) and streams it one at a time. Glob supported
gcs-jsonl	GCSJSONLinesDataset	dict	As gcs, but also opens the JSONLines file(s) and streams one line at a time. Glob supported
elk	ELKDataset	dict	Connects to ELK instance, runs json query specified in path, then returns the resulting docs one at a time
rest	RESTDataset	dict	Streams the response from a REST API.

TextDataset

Name	Type	Required	Default	Description
path	Union[List[str]], str]	Yes		The local path to be loaded
encoding	str	No	'utf-8'	The encoding to be used when opening the file
allowed_extensions	Sequence[str]	No	None	The supported extensions (others will be discarded). None means all extensions

Returned element type: str

CSVDataset

Name	Type	Required	Default	Description
path	Union[List[str], str]	Yes		The local path to be loaded
encoding	str	No	'utf-8'	The encoding to be used when opening the file
allowed_extensions	Sequence[str]	No	('csv')	The supported extensions (others will be discarded). None means all extensions
delimiter	str	No	','	The column delimiter

Returned element type: dict. Each element represent a row from the CSV(s). The keys are the CSV column names.

JSONDataset

Name	Type	Required	Default	Description
path	Union[List[str], str]	Yes		The local path to be loaded
encoding	str	No	'utf-8'	The encoding to be used when opening the file
allowed_extensions	Sequence[str]	No	('json')	The supported extensions (others will be discarded). None means all extensions

Returned element type: dict. This dictionary directly maps the JSON file.

JSONLinesDataset

Name	Type	Required	Default	Description
path	Union[List[str], str]	Yes		The local path to be loaded
encoding	str	No	'utf-8'	The encoding to be used when opening the file
allowed_extensions	Sequence[str]	No	('json', 'jsonl')	The supported extensions (others will be discarded). None means all extensions

Returned element type: dict. This dictionary maps a single JSON line from the file.

GCSDataset

Name	Type	Required	Default	Description
path	Union[List[str], str]	Yes		The remote path to be loaded
download_path	str	No	'$HOME/.cache/data-engineering'	The path where the file(s) will be downloaded
service_account	str	No	None	The service account path to use. If missing will use the default user account
project	str	No	None	The project id to use. If missing will use the user configured project it

Returned element type: str. Each element represent a local path where to find the file downloaded from GCS.

GCSTextDataset

Name	Type	Required	Default	Description
path	Union[List[str], str]	Yes		The remote path to be loaded
download_path	str	No	'$HOME/.cache/data-engineering'	The path where the file(s) will be downloaded
service_account	str	No	None	The service account path to use. If missing will use the default user account
project	str	No	None	The project id to use. If missing will use the user configured project it
encoding	str	No	'utf-8'	The encoding to be used when opening the file

Returned element type: str. Each element represent a line from the remote file.

GCSCSVDataset

Name	Type	Required	Default	Description
path	Union[List[str], str]	Yes		The remote path to be loaded
download_path	str	No	'$HOME/.cache/data-engineering'	The path where the file(s) will be downloaded
service_account	str	No	None	The service account path to use. If missing will use the default user account
project	str	No	None	The project id to use. If missing will use the user configured project it
encoding	str	No	'utf-8'	The encoding to be used when opening the file
allowed_extensions	Sequence[str]	No	('csv')	The supported extensions (others will be discarded). None means all extensions
delimiter	str	No	','	The column delimiter

Returned element type: dict. Each element represent a row from the CSV(s). The keys are the CSV column names.

GCSJSONDataset

Name	Type	Required	Default	Description
path	Union[List[str], str]	Yes		The remote path to be loaded
download_path	str	No	'$HOME/.cache/data-engineering'	The path where the file(s) will be downloaded
service_account	str	No	None	The service account path to use. If missing will use the default user account
project	str	No	None	The project id to use. If missing will use the user configured project it
encoding	str	No	'utf-8'	The encoding to be used when opening the file
allowed_extensions	Sequence[str]	No	('json')	The supported extensions (others will be discarded). None means all extensions

Returned element type: dict. Each element is a dict directly mapping a JSON file.

GCSJSONLinesDataset

Name	Type	Required	Default	Description
path	Union[List[str], str]	Yes		The remote path to be loaded
download_path	str	No	'$HOME/.cache/data-engineering'	The path where the file(s) will be downloaded
service_account	str	No	None	The service account path to use. If missing will use the default user account
project	str	No	None	The project id to use. If missing will use the user configured project it
encoding	str	No	'utf-8'	The encoding to be used when opening the file
allowed_extensions	Sequence[str]	No	('json', 'jsonl')	The supported extensions (others will be discarded). None means all extensions

Returned element type: dict. Each element is a dict mapping a JSON line from the file(s).

ELKDataset

Name	Type	Required	Default	Description
path	Union[List[str], str]	Yes		The local path to a query written in JSON
host	str	Yes		Elastic host URL
port	str	Yes		Elastic host port
username	str	Yes		Elastic authentication username
password	str	Yes		Elastic authentication password
index	str	Yes		Elastic index to query
start_isodate	str (ISO datetime)	Yes		Elastic start date range with format: "2021-09-15T10:00:00.000Z"
end_isodate	str (ISO datetime)	Yes		Elastic end date range with format: "2021-09-15T10:00:00.000Z"
date_field	str	No	@timestamp	Elastic date field. Can be nested into list, eg. "messages.date"

Returned element type: dict. Each element is a document matching the given query.

RESTDataset

Name	Type	Required	Default	Description
download_path	str	No	'$HOME/.cache/data-engineering'	Where to download data
headers	dict	No	{}	Call Headers
auth_headers	dict	No	{}	Authentication headers
params	Optional[dict]	No	None	URL key value params
method	str	No	'GET'	Call method, 'GET', 'POST'...
next_url_f	Callable[[dict], Optional[str]]	No	lambda x: None	Function to extract the next url to call from the json response for paginated APIs. Should return None to mark the end or the URL string

Returned element type: dict representing the json response.

Custom datasets

Method 1. Functional style

def my_load(path, **kwargs):
    ds = (dfn
        .load('json', path=path, **kwargs)
        .filter(lambda x: x['KEY'] > 10)
        .map(lambda x: x**2)
    )
    return ds

Method 2. Extend Dataset

Write classes

@dataclass
class ELKDatasetConfig(dfn.Config):
    # Additional arguments to base class
    host: str
    port: int

class ELKDataset(dfn.DatasetSource):
    def __init__(self, config, **kwargs):
        super().__init__(config=config, **kwargs)
        self.elk_client = elklib(self.config.host, self.config.port)

    def dataset_name() -> str:
        return 'elk-dataset'

    def info(self) -> dict:
        return {
            'description': 'My ELK dataset class.',
            'author': '[e-mail]',
            'date': '2021-09-01',
        }

    def schema(self) -> dict:
        return {
            'column_1': 'int',
            ...
        }
        # this method may also load a row and infer it, like CSVDataset does

    def _generate_examples(self) -> Generator:
        for doc in self.elk_client.scroll_function():
            # Apply some prep to the document
            yield doc

Add new dataset to list of supported datasets

• Add a line to DATASETS in datafun/__init__.py:

DATASETS = {
    ...
    "elk-dataset": ELKDataset,
}

Use it!

ds = dfn.load('elk-dataset', config={
    'host': 'localhost',
    'port': '8888',
})