Nesting context managers

The other day I used tempfile to create two temporary files inside a temporary directory. I’ve used python for so long that I never realized that since python 3.8 we can write the following much shorter:

# the old way
import tempfile

with TemporaryDirectory() as temp_dir:
    with NamedTemporaryFile(suffix=".pdf") as temp_pdf_file:
      with NamedTemporaryFile(suffix=".zip") as temp_zip_file:
        ...

# the new way
with (
    TemporaryDirectory() as temp_dir,
    NamedTemporaryFile(suffix=".pdf") as temp_pdf_file,
    NamedTemporaryFile(suffix=".zip") as temp_zip_file,
):
    ...

and this works for all context managers, not just tempfile.

In this example, unfortunately temp_dir won’t be created until the with block actually enters, so if we want to create the temporary files in the same directory, we will need to do it like this:

with TemporaryDirectory() as temp_dir:
    with (
        NamedTemporaryFile(suffix=".pdf", dir=temp_dir) as temp_pdf_file,
        NamedTemporaryFile(suffix=".zip", dir=temp_dir) as temp_zip_file,
    ):
        ...