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python relative import from same package fails

I am working on a project involving the popular aiortc/aioquic github package. Located at src/aioquic/buffer.py there is an import statement:
from ._buffer import Buffer, BufferReadError, BufferWriteError # noqa
This line is meant to import a C/stub module _buffer.c / _buffer.pyi . When used from the root directory to run examples found in the examples directory this import line will work, but when trying to run in a Docker container from the same directory this import fails and when importing from the /src directory the import fails. I have tried reading several other questions on python relative imports but none seem to make sense to me.
To reproduce the issue:
open python in the src directory
from aioquic import about (works)
from aioquic import buffer (fail)
from aioquic import buffer
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/aioquic/src/aioquic/buffer.py", line 1, in <module>
from ._buffer import Buffer, BufferReadError, BufferWriteError # noqa
ModuleNotFoundError: No module named 'aioquic._buffer'
I don't understand why the examples http3_client and http3_server work but when trying to import it directly it fails. I thought I understood roughly how to use python imports but apparently not. What would cause the same line to work when running from one directoy but fail when running from another directory? Is it something magical with the PYTHONPATH? I'm hoping someone smarter than I am can explain why this is failing.
[EDIT and most importantly how to fix this so the import will work nomatter where the user runs python from. I have tried several different combinations but none seem to work.]
Thanks in advance.

I figured out what was wrong.
The stub/C module had to be built into a .pyd file before it could imported. This was done by
pip install -e .
on the parent directory

Is it something magical with the PYTHONPATH?
Yes.
Typically . dot (current working directory) will appear
in that exported env var,
so where you started matters.
Take care to ensure you're using the same env var setting,
and the same pwd,
during both the interactive and the Docker runs.

how to import modules from local repository with virtualenv and pip

I have a question that I assume has a simple answer, but for some reason I am struggling to find it on my own. I have created and activated a virtual environment with virtualenv, and I am trying to install all the necessary packages in order to create a requirements.txt file.
I have, for example, a Python file that begins like this:
import xml.etree.ElementTree as ET
from lib.project import Projector
from lib import writer
import os
import datetime
from datetime import timedelta
from datetime import datetime
import pprint
When I try to run this file from the virtual machine, I receive the following error:
Traceback (most recent call last):
File "readMap.py", line 2, in <module>
from lib.project import Projector
ModuleNotFoundError: No module named 'lib.project'
My problem is that I'm not sure why the virtual environment can't find project.py. My directory structure is:
regiaoSul
lib
__init__.py
arrival_conversion.py
coord_conversion.py
message_conversion.py
project.py
route_conversion.py
stop_conversion.py
wkt_parser.py
writer.py
readMap.py
json_generator.py

The import on line 2 implies lib is a module rather than "a simple repository".
I will try running the script with the flag -m. Something like this -
python -m script_name
make sure to drop the .py extension when you run with -m flag.
Another advice: you don't need to install python files to the virtual environment, they are not some external libraries. They only need to be present (with the same order of packaging) when you run your script.

Thanks to everyone who responded. I believe the issue was some sort of dependency problem. In readMap.py I had imported writer from lib, and in writer.py I had imported Projector from project. I moved the function that required Projector from writer.py to readMap.py and it worked.
I still don't fully understand why this was a problem. Until recently I had been running my scripts in PyCharm and they all worked with the structure I had. It was only when I tried to run them from the command line in my virtual machine that they didn't work.
If anybody would like to explain the distinction to me and what the exact problem was with my imports, feel free to.

I sometimes face the same issue. A solution is to add the path to sys.path by:
import sys
sys.path.insert(0, "/path/to/your/package_or_module")

How to import my python file in another file in visual studio code

I am using python/selenium in visual studio code. I am trying to import my another python class driverScript which resides in executionEngine module and in the file DriverScript. I have imported as below:
import driverScript from executionEngine.DriverScript
It is producing error:
Traceback (most recent call last):
File "c:/Selenium/Selenium-Python Framework/RK_Practice/Tests/mainTest.py", line 5, in <module>
from executionEngine.DriverScript import driverScript
ModuleNotFoundError: No module named 'executionEngine'
How can I import correctly? Your help is very much appreciated.

If the script you are wishing to import is not in the current directory, you may want to take this approach:
import sys
sys.path.insert(1, '/path/to/script/folder')
import driverScript from executionEngine.DriverScript

If your python file is on the same level in dir, then you can import just by calling:
import filename
If your python file is inside another folder, then you need to create a blank __init__.py file that will help python to understand it's a package. Then you can import that as follows:
from folderName import filename

Depends on where executionEngine is supposed to come from. If it's from a package installable via a package manager such as pip or Anaconda, looks like it's not properly installed. If you installed it yourself, you probably need to add the directory containing executionEngine to your PYTHONPATH, so the Python interpreter can find it. This can be done in the VSCode environment files. See the PYTHONPATH section in https://code.visualstudio.com/docs/python/environments

Having an issue creating an exe with py2exe and script importing xlrd

My goal is to create a python script that loops over cells of an excel document. This is my python script called reader.py, and it works just fine.
import xlrd
import os
exceldoc = raw_input("Enter the path to the doc [C:\\folder\\file.xlsx]: ")
wb = xlrd.open_workbook(exceldoc,'rb')
.... some code....
The problem I'm encountering is attempting to use py2exe to create an executable so this script can be used elsewhere.
Here is my setup.py file:
from distutils.core import setup
import py2exe
import sys
from glob import glob
setup(name='Excel Document Checker',console=['reader.py'])
I run the following command: python setup.py py2exe
It appears to run fine; it creates the dist folder that has my reader.exe file, but near the end of the command I get the following:
The following modules appear to be missing
['cElementTree', 'elementtree.ElementTree']
I did some searching online, and tried the recommendations here Re: Error: Element Tree not found, this changing my setup.py file:
from distutils.core import setup
import py2exe
import sys
from glob import glob
options={
"py2exe":{"unbuffered": True,"optimize": 2,
'includes':['xml.etree.ElementPath', 'xml.etree.ElementTree', 'xml.etree.cElementTree'],
"packages": ["elementtree", "xml"]}}
setup(name='Excel Document Checker',options = options,console=['reader.py'])
I'm now getting an error:
ImportError: No module named elementtree
I'm sort of at an impasse here. Any help or guidance is greatly appreciate.
Just some information - I'm running Python 2.6 on a 32 bit system.

You explicitly told setup.py to depend on a package named elementtree here:
"packages": ["elementtree", "xml"]}}
There is no such package in the stdlib. There's xml.etree, but obviously that's the same name.
The example you found is apparently designed for someone who has installed the third-party package elementtree, which is necessary if you need features added after Python 2.6's version of xml.etree, or if you need to work with Python 1.5-2.4, but not if you just want to use Python 2.6's version. (And anyway, if you do need the third-party package… then you have to install it or it won't work, obviously.)
So, just don't do that, and that error will go away.
Also, if your code—or the code you import (e.g., xlrd) is using xml.etree.cElementTree, then, as the py2exe FAQ says, you must also import xml.etree.ElementTree before using it to get it working. (And you also may need to specify it manually as a dependency.)
You presumably don't want to change all the third-party modules you're using… but I believe that making sure to import xml.etree.ElementTree before importing any of those third-party modules works fine.

Python: Submodules Not Found

My Python couldn't figure out the submodules when I was trying to import reportlab.graphics.shapes like this:
>>> from reportlab.graphics.shapes import Drawing
Traceback (most recent call last):
File "<pyshell#14>", line 1, in <module>
from reportlab.graphics.shapes import Drawing
ImportError: No module named shapes
I have copied the reportlab package to /site-packages and I can import module reportlab.graphics successfully.
My Python version is 2.7.3.
Could anyone help me to fix this problem?

As #dan-boa pointed out, you can add paths to the module search path, but since you can find the parent module, I doubt that this is your root problem.
Do you have some left-over installation of the module at another path? You can check the path where it is finding the parent package (reportlab) by executing:
import reportlab
print reportlab.__file__
If this is indeed the path you were expecting, then try this recursively with the the sub-modules, until you can see where the problem is. Perhaps, your package is corrupted? Try manually checking in the path returned if you can find the files/modules in question.
If this is not the path you were expecting, clean-up the installation from this 2nd path and try again.
Finally, in case you do find that it is a path problem, instead of adding the path each time using sys.path.append, you can add it to PYTHONPATH

Please check your sys path and if the directory of the module is not present then add it.
import sys
sys.path.append('PATH_OF_THE_MODULE')
As site-packages is already their in the sys.path, may be therefore the package was imported successfully.