Py 3: Terminal script can't find relative path

[Gnarlodious]

I am running a script in a browser that finds the file in subfolder
Data:

Content=Plist('Data/Content.plist')

However, running the same script in Terminal errors:

IOError: [Errno 2] No such file or directory: 'Data/Content.plist'

Is Py 3 unable to find relative paths? I tried all kinds of tricks to
no avail. What is wrong?

-- Gnarlie