Create a Smart Python Read Component

In this guide, we'll build a Smart Python Read Component that leverages Ascend's Smart partitioning feature to efficiently ingest partitioned datasets by discovering and processing partitions in parallel.

Prerequisites

• Ascend Flow

Create a new Component

Begin from your workspace Super Graph view. Follow these steps to create your component:

Using the Component Form

1. Double-click the Flow where you want to create your component
2. Right-click anywhere in the Flow Graph
3. Hover over Create Component, then over Read in the expanded menu, and click From Scratch
4. Complete the form with these details:
   • Select your Flow
   • Enter a descriptive Component Name like read_sales
   • Select Python as your file type

Using the Files Panel

1. Open the files panel in the top left corner
2. Navigate to and select your desired Flow
3. Right-click on the components directory and choose New file
4. Name your file with a descriptive name like read_sales.py and press enter

Create your Smart Python Read Component

Structure your Smart Python Read Component following this pattern, based on our Otto's Expeditions project:

1. Import necessary packages: Include Ascend resources (reader), context handlers (ComponentExecutionContext), data processing libraries (Polars and pyarrow in this examples), filesystem libraries (gcsfs in this examples), and logging utilities (log)
2. Define a partition listing function with the @reader.list() decorator: Discover and yield partitions to process
3. Define a partition read function with the @reader.read() decorator: Read each partition identified by the listing function
4. Return structured data: Ensure the read function returns an Arrow table for efficient downstream processing

The @reader.list() and @reader.read() decorators integrate into Ascend's Smart partitioning framework, enabling parallel ingestion across data partitions.

Example

smart_read.py

import gcsfs
import polars as pl
import pyarrow as pa

from ascend.resources import reader
from ascend.resources.reader import ListItem
from ascend.common.events import log
from ascend.application.context import ComponentExecutionContext


@reader.list()
def list_partitions(context: ComponentExecutionContext):
    """List parquet file partitions for metabook events."""
    fs = gcsfs.GCSFileSystem()
    files = fs.glob("gs://ascend-io-gcs-public/ottos-expeditions/lakev0/generated/events/metabook.parquet/year=*/month=*/day=*/*.parquet")
    files = [ListItem(name=file) for file in files]
    log(f"Found {len(files)} partitions")
    yield from files


@reader.read()
def read_partition(context: ComponentExecutionContext, item: ListItem) -> pa.Table:
    """Read a single partition of metabook events."""
    log(f"Reading partition {item.name}")
    df = pl.read_parquet(f"gs://{item.name}")
    return df.to_arrow()

Check out our reference guide for additional examples and advanced options.

🎉 Congratulations! You've successfully created a Smart Python Read Component in Ascend.