BadZipfile "file is not a zip file"

[webcomm]

On Jan 8, 8:02 pm, MRAB <goo... at mrabarnett.plus.com> wrote:
> You're just creating a file called "data.zip". That doesn't make it a
> zip file. A zip file has a specific format. If the file doesn't have
> that format then the zipfile module will complain.

Hmm.  When I open it in Windows or with 7-Zip, it contains a text file
that has the data I would expect it to have.  I guess that alone
doesn't necessarily prove it's a zip file?

datum is something I'm downloading via a web service.  The providers
of the service say it's a zip file, and have provided a code sample in
C# (which I know nothing about) that shows how to deal with it.  In
the code sample, the file is base64 decoded and then unzipped.  I'm
trying to write something in Python to decode and unzip the file.

I checked the file for comments and it has none.  At least, when I
view the properties in Windows, there are no comments.