Answer: `# Databricks notebook source `

The first line of a Databricks Python notebook when viewed in a text editor is a special comment that identifies the file as a Databricks notebook. This line is always `# Databricks notebook source` for Python notebooks. Other options like `//` (Scala) or `--` (SQL) are used for notebooks in those languages, but the question specifically refers to a Python notebook. Magic commands like `%python` or `# MAGIC %python` appear in cell content, not as the first line of the notebook file.

Author: LeetQuiz Editorial Team