python#

Databricks Connect

Databricks Connect allows you to connect your favorite IDE (PyCharm, VSCode, etc.) and other custom applications to Databricks compute and run Spark (or non-Spark) code.

This post is not a comprehensive guide on Databricks Connect; rather, it consists of side notes from the Azure Databricks docs. Most of the notes also apply to Databricks on AWS and GCP.

Generating Azure OAuth2 Access Token By Python

There are two modern ways to generate an Azure OAuth2 access token using Python: one is by using the MSAL library, and the other is by using the Azure Identity library, which is based on the former.

There're also other ways to get the token, like using the requests or aiohttp libraries etc. to send a POST request to the Azure OAuth2 token endpoint, but it's not recommended. As the MSAL and Azure Identity libraries are the official libraries provided by Microsoft, they are more secure and easier to use. For e.g. they handle token caching, token refreshing, and token expiration automatically. Furthermore, some of the credential types are difficult (too many code) to be implemented by raw requests or aiohttp.

Python adding version info to docstrings

When checking PySpark's source code, find a nice way it uses to add version information to docstrings by a @since() decorator. Here is an example:

Python thread safe operations

Quick example from the official Python documentation about thread safety in Python:

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L.append(x)
L1.extend(L2)
x = L[i]
x = L.pop()
L1[i:j] = L2
L.sort()
x = y
x.field = y
D[x] = y
D1.update(D2)
D.keys()

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i = i+1
L.append(L[-1])
L[i] = L[j]
D[x] = D[x] + 1

It's important to understand that Python, due to its Global Interpreter Lock (GIL), can only switch between threads between bytecode instructions. The frequency of these switches can be adjusted using sys.setswitchinterval(). This ensures that within a single bytecode instruction, Python will not switch threads, making the operation atomic (thread-safe). For a deeper dive into this topic, you can read this discussion on atomic and thread-safe operations in Python.

Generating .env file

During local testing, we often need to set environment variables. One way to do this is to create a .env file in the root directory of the project. This file contains key-value pairs of environment variables. For example, a .env file might look like this:

ENV=dev
SECRET=xxx

Hereunder a quick bash script to generate a .env file from a list of Azure KeyVault secrets, same logic can be applied to other secret managers.

Generating ERD from sqlalchemy

This posts tests some popular Python tools (sqlalchemy_data_model_visualizer , sqlalchemy_schemadisplay, and eralchemy2) to generate ERD (Entity-Relation Diagram) from sqlalchemy models.

The test code can be found in this Github repo.

Profiling Python code

Interesting reading:

• [2023] Profiling in Python: How to Find Performance Bottlenecks
• [2023][Podcast] Measuring Multiple Facets of Python Performance With Scalene
• [2019][PDF] A Survey of Open-Source Python Profilers by Peter Norton
• [2020] Why you should try VizTracer to understand your python program
• [2023] How to Profile Asyncio Programs with cProfile

Running asyncio task in Databricks

Standard method to run asyncio task is as simple as asyncio.run(main()). But in Databricks, it is not that simple. With the same command, you will get the following error:

import asyncio
async def main():
    await asyncio.sleep(1)
asyncio.run(main())

RuntimeError: asyncio.run() cannot be called from a running event loop

Indeed, in Databricks, we've already in a running loop:

import asyncio
asyncio.get_running_loop()

<_UnixSelectorEventLoop running=True closed=False debug=False>

Convert json to parquet and send to Azure Blob Storage

Load a local json file into a PyArrow table, then write it to a parquet file in Azure Blob Storage without using pandas.

Dockerfile with secrets

The most secure way to use secrets in a Dockerfile is to use the --secret flag in the docker build command. This way, the secret is not stored in the image, and it is not visible in the Dockerfile.

A common use case in Python world is to install packages from a private PyPI repository in a Dockerfile. Suppose during the CICD pipeline, there's an environment variable called PIP_INDEX_URL where holds this private PyPI credentials.

Check the official Build secrets doc.