Definition metadata - Asset descriptions

When defined, asset descriptions will be displayed in the Dagster UI alongside the asset. There are two ways to add an asset description:

• Using Python docstrings
• Using the asset decorator’s description parameter

Using docstrings

As you went through this course, you might have noticed that the assets all contain docstrings. A Python docstring, or documentation string, embeds documentation about a class, module, function, or method definition in the code itself. While code comments serve a similar purpose, docstrings support built-in Python functionality, like help.

Docstrings are defined by including a string, surrounded by triple quotes (”””) as the first statement in an object’s definition. For example:

from dagster import asset

@asset
def taxi_zones_file() -> None:
    """
      The raw CSV file for the taxi zones dataset. Sourced from the NYC Open Data portal.
    """
    raw_taxi_zones = requests.get(
        "https://data.cityofnewyork.us/api/views/755u-8jsi/rows.csv?accessType=DOWNLOAD"
    )

    with open(constants.TAXI_ZONES_FILE_PATH, "wb") as output_file:
        output_file.write(raw_taxi_zones.content)

Using the description parameter

Another way to add a description to an asset is to use the asset decorator with the description parameter. Note: This will override any docstrings in the Dagster UI.

For example:

from dagster import asset

@asset(
    description="The raw CSV file for the taxi zones dataset. Sourced from the NYC Open Data portal."
)
def taxi_zones_file() -> None:
    """
      This will not show in the Dagster UI
    """
    raw_taxi_zones = requests.get(
        "https://data.cityofnewyork.us/api/views/755u-8jsi/rows.csv?accessType=DOWNLOAD"
    )

    with open(constants.TAXI_ZONES_FILE_PATH, "wb") as output_file:
        output_file.write(raw_taxi_zones.content)

Asset descriptions in the Dagster UI

Now that you understand how to define asset descriptions, let’s take a look at them in the Dagster UI.