[Tutor] Help with Package Importing

[Colin Daly]

Thank you for the reply, Mats. Your suggestion yielded the following error:

  from . import SubProgram1 as s1

ImportError: attempted relative import with no known parent package

On Wed, Mar 2, 2022 at 6:00 AM Mats Wichmann <mats at wichmann.us> wrote:

> On 3/1/22 22:15, Colin Daly wrote:
> > Hello,
> >
> > I have a question about how to properly import packages. I had created a
> > basic nested program in order to clearly show my error, but it doesn't
> look
> > like I can upload files for sharing. Please excuse me as this is my first
> > time posting here.
> >
> > I have the following folder and file structure:
> >
> > /MainDirectory
> > MainFile.py
> > | -- / Sub 1
> > | -- | -- SubProgram1_1.py
> > | -- | -- SubProgram1.py
> > | -- / Sub 2
> > | -- | -- ReadFile.py
> >
> > I'm working out of MainDirectory. In MainFile.py I have:
> >
> > MainFile.py
> > ********************************************************
> > import Sub1.SubProgram1_1 as s1_1
> >
> > def DoSomething():
> >        z = s1_1.SubFunc1_2()
> >        print(z)
> >
> > DoSomething()
> >
> > ********************************************************
> >
> > And inside ./Sub1/SubProgram1_1 I have
> >
> > SubProgram1_1.py
> > ********************************************************
> > import Sub1.SubProgram1 as s1
> >
> > def SubFunc1_2():
> >
> >      xx = s1.SubFunc1()
> >     yy = xx + 22
> >     return yy
> >
> > def main():
> >     n = SubFunc1_2()
> >
> >     print(f"you are in subprogram1_1. value from SubFunc1_2 is {n}")
> >
> > if __name__ == "__main__":
> >     main()
> >
> > ********************************************************
> >
> > MainFile.py runs fine like this, but SubProgram1_1.py does not run like
> > this. I need to change
> > import Sub1.SubProgram1 as s1
> > to
> > import SubProgram1 as s1
> >
> > How should I have things such that I can run MainFile.py and
> > SubProgram1_1.py without messing with the import statements. Best I can
> > tell is to add the following to SubProgram1_1.py:
> >
> > import os, sys
> > sys.path.insert(0, os.path.join(os.path.split(__file__)[0], ".."))
> >
> > but that seems not very clean. Why should SubProgram1_1 need to import
> > Sub1.SubProgram1_1 when it's in the same folder?
>
> Because it's not in the same file, Python sees it as a separate module
> (the directory makes it a package, but it's still has multiple modules).
>  Try it this way, which may be more readable to you:
>
> from . import SubProgram1 as s1
>
>
> BTW, Importing as a different name will probably lead to confusion at
> some point. I know there are a few places where it's done a lot (import
> numpy as np) but using the name of the module makes it easier to keep
> track of what you're doing - and for other readers to be able to find
> the context more quickly.  That's just a suggestion, it's not any kind
> of rule - if you weren't allowed to "import as" the facility wouldn't
> exist!
>
>