You can use triple-quoted strings. When they're not a docstring (the first thing in a class/function/module), they are ignored.

This is a multiline

(Make sure to indent the leading ''' appropriately to avoid an IndentationError.)

Guido van Rossum (creator of Python) tweeted this as a "pro tip".

However, Python's style guide, PEP8, favors using consecutive single-line comments, and this is also what you'll find in many projects. Text editors usually have a shortcut to do this easily.