The Data Catalog

Note: This documentation is based on Kedro 0.14.3, if you spot anything that is incorrect then please create an issue or pull request.

This section introduces catalog.yml, the project-shareable Data Catalog. The file is located in conf/base and is a registry of all data sources available for use by a project; it manages loading and saving of data.

Using the Data Catalog within Kedro configuration

Kedro uses configuration to make your code reproducible when it has to reference datasets in different locations and/or in different environments.

You can copy this file and reference additional locations for the same datasets. For instance, you can use the catalog.yml file in conf/base/ to register the locations of datasets that would run in production while copying and updating a second version of catalog.yml that can be placed in conf/local/ to register the locations of sample datasets on the local computer that you are using for prototyping your data pipeline.

There is built-in functionality for conf/local/ to overwrite conf/base/ detailed here. This means that a dataset called cars could exist in the catalog.yml files in conf/base/ and code/local/. In code, in src, you would only call a dataset named cars and Kedro would detect which definition of cars dataset to use to run your pipeline - cars definition from code/local/catalog.yml would take precedence in this case.

The Data Catalog also works with the credentials.yml in conf/local/, allowing you to specify usernames and passwords that are required to load certain datasets.

The are two ways of defining a Data Catalog: through the use of YAML configuration, or programmatically using an API. Both methods allow you to specify:

  • Dataset name
  • Dataset type
  • Location of the dataset (includes file paths, S3 bucket locations and more)
  • Credentials needed in order to access the dataset
  • Load and saving arguments
  • Whether or not you want a dataset or ML model to be versioned when you run your data pipeline

Using the Data Catalog with the YAML API

The YAML API allows you to configure your datasets in a YAML configuration file, conf/base/catalog.yml or conf/local/catalog.yml.

Here is an example data config catalog.yml:

# Example 1: Loads a local csv file
  type: CSVLocalDataSet
  filepath: "data/01_raw/bikes.csv"

# Example 2: Loads and saves a local csv file using specified load and save arguments
  type: CSVLocalDataSet
  filepath: data/01_raw/company/cars.csv
    sep: ','
    index: False
    date_format: '%Y-%m-%d %H:%M'
    decimal: '.'

# Example 3: Loads a csv file from a specific S3 bucket that requires credentials and additional load arguments
  type: CSVS3DataSet
  filepath: data/02_intermediate/company/motorbikes.csv
  credentials: dev_s3
  bucket_name: test_bucket
    sep: ','
    skiprows: 5
    skipfooter: 1
    na_values: ['#NA', 'NA']

# Example 4: Loads a local pickle dataset
  type: PickleLocalDataSet
  filepath: data/06_models/airplanes.pkl
  backend: pickle

# Example 5: Loads a local hdf dataset, specifies the selection of certain columns to be loaded as well as overwriting the file when saving
  type: HDFLocalDataSet
  filepath: data/02_intermediate/skateboards.hdf
  key: name
    columns: ['brand', 'length']
    mode: 'w'  # Overwrite even when the file already exists
    dropna: True

# Example 6: Loads a local parquet dataset with load and save arguments
  type: ParquetLocalDataSet
  filepath: data/02_intermediate/trucks.parquet
    columns: ['name', 'gear','disp', 'wt']
    categories: list
    index: 'name'
     compression: 'GZIP'
     file_scheme: 'hive'
     has_nulls: false
     partition_on: ['name']

# Example 7: Loads a SQL table with credentials, load and save arguments
  type: SQLTableDataSet
  credentials: scooters_credentials
  table_name: scooters
    index_col: ['name']
    columns: ['name', 'gear']
    if_exists: 'replace'

# Example 8: Load a SQL table with credentials and applies a SQL query to the table
  type: SQLQueryDataSet  
  credentials: scooters_credentials
  sql: 'select * from cars where gear=4'
    index_col: ['name']

The above catalog.yml gets dev_s3 scooters_credentials from conf/local/credentials.yml:

     aws_access_key_id: token
     aws_secret_access_key: key    

  con: sqlite:///kedro.db

Loading multiple datasets that have similar configuration

You may encounter situations where your datasets use the same file format, load and save arguments, and are stored in the same folder. The YAML has a built-in syntax for factorising parts of a YAML file, which means that you can decide what is generalisable across your datasets so that you do not have to spend time copying and pasting dataset configurations in catalog.yml.

You can see this in the following example:

_csv: &csv
  file_format: 'csv'
    sep: ','
    na_values: ['#NA', 'NA']
    header: True
    inferSchema: False

  <<: *csv
  filepath: 's3a://data/01_raw/cars.csv'

  <<: *csv
  filepath: 's3a://data/01_raw/trucks.csv'

  <<: *csv
  filepath: 's3a://data/01_raw/bikes.csv'
    header: False

The syntax &csv names the following block csv and the syntax <<: *csv inserts the contents of the block named csv. Locally declared keys entirely override inserted ones as seen in bikes.

Note: It’s important that the name of the template entry starts with a _ so Kedro knows not to try and instantiate it as a dataset.

You can also nest reuseable YAML syntax:

_csv: &csv
  file_format: 'csv'
  load_args: &csv_load_args
    header: True
    inferSchema: False

  <<: *csv
  filepath: 's3a://data/01_raw/airplanes.csv'
    <<: *csv_load_args
    sep: ';'

In this example the default csv configuration is inserted into airplanes and then the load_args block is overridden. Normally that would replace the whole dictionary. In order to extend load_args the defaults for that block are then re-inserted.

Transcoding datasets

You may come across a situation where you would like to read the same file using two different dataset implementations. For instance, parquet files can not only be loaded via the ParquetLocalDataSet, but also directly by SparkDataSet using pandas. To do this, you can can define your catalog.yml as follows:

  type: ParquetLocalDataSet
  filepath: data/01_raw/data.parquet

    filepath: data/01_raw/data.parquet

In your pipeline, you may refer to either dataset as input or output, and it will ensure the dependencies point to a single dataset mydata both while running the pipeline and in the visualisation.

Transforming datasets

If you need to augment the loading and / or saving of one or more datasets you can use the transformer API. To do this create a subclass of AbstractTransformer that implements your changes and then apply it to your catalog with DataCatalog.add_transformer. For example to print the runtimes of load and save operations you could do this:

class PrintTimeTransformer(AbstractTransformer):
    def load(self, data_set_name: str, load: Callable[[], Any]) -> Any:
        start = time.time()
        data = load()
        print("Loading {} took {:0.3f}s".format(data_set_name, time.time() - start))
        return data

    def save(self, data_set_name: str, save: Callable[[Any], None], data: Any) -> None:
        start = time.time()
        print("Saving {} took {:0.3}s".format(data_set_name, time.time() - start))


By default transformers are applied to all datasets in the catalog (including any that are added in the future). The DataCatalog.add_transformers method has an additional argument data_set_names that lets you limit which data sets the transformer will be applied to.

Versioning datasets and ML models

Making a simple addition to your Data Catalog allows you to perform versioning of datasets and machine learning models.

Consider the following versioned dataset defined in the catalog.yml:

  type: CSVLocalDataSet
  filepath: data/01_raw/company/cars.csv
  versioned: true

The DataCatalog will create a versioned CSVLocalDataSet called cars.csv. The actual csv file location will look like data/01_raw/company/cars.csv/<version>/cars.csv, where <version> corresponds to a global save version string formatted as

This section shows just the very basics of versioning. You can learn more about how this feature can be used in Advanced IO.

Using the Data Catalog with the Code API

The code API allows you to configure data sources in code. This can also be used to operate the IO module within notebooks.

from import *
import os

Configuring a data catalog

In a file like, you can generate the Data Catalog. This will allow everyone in the project to review all the available data sources. In the following, we are using the pre-built CSV loader, which is documented in the API reference documentation: CSVLocalDataSet

io = DataCatalog({
  'bikes': CSVLocalDataSet(filepath='../data/01_raw/bikes.csv'),
  'cars': CSVLocalDataSet(filepath='../data/01_raw/cars.csv', load_args=dict(sep=',')), # additional arguments
  'cars_table': SQLTableDataSet(table_name="cars", credentials=dict(con="sqlite:///kedro.db")),
  'scooters_query': SQLQueryDataSet(sql="select * from cars where gear=4", credentials=dict(con="sqlite:///kedro.db")),
  'ranked': ParquetLocalDataSet(filepath="ranked.parquet")

Loading datasets

Each dataset can be accessed by its name.

cars = io.load('cars') # data is now loaded as a DataFrame in 'cars'
gear = cars['gear'].values

Behind the scenes

The following steps happened behind the scenes when load was called:

  • The value cars was located in the Data Catalog
  • The corresponding AbstractDataSet object was retrieved
  • The load method of this dataset was called
  • This load method delegated the loading to the underlying pandas read_csv function

Viewing the available data sources

If you forget what data was assigned, you can always review the DataCatalog.


Saving data

Saving data can be completed with a similar API.

Note: This use is not recommended unless you are prototyping in notebooks.

Saving data to memory

memory = MemoryDataSet(data=None)
io.add('cars_cache', memory)'cars_cache', 'Memory can store anything.')

Saving data to a SQL database for querying

At this point we may want to put the data in a SQLite database to run queries on it. Let’s use that to rank scooters by their mpg.

# This cleans up the database in case it exists at this point

except FileNotFoundError:
    pass'cars_table', cars)
ranked = io.load('scooters_query')[['brand', 'mpg']]

Saving data in parquet

Finally we can save the processed data in Parquet format.'ranked', ranked)

Creating your own dataset

More specialised datasets can be found in contrib/io. Creating new datasets is the easiest way to contribute to the Kedro project.