Python import statements

The following rules apply to any import statement in the code base:

All imports must be absolute, unless they import individual pieces of an integrated code component that is only split across several source code files for technical or organizational reasons.
Imports must be placed at the top of a source file, unless there is a specific reason not to do so (e.g., delayed import due to performance concerns, circular dependencies). If such a reason exists, it must be documented by a comment at the import statement.
There must be no more than one import per line.
Multiple individual imports from a single module must follow the pattern:
```
from <module> import (
    symbol1,
    symbol2,
)
```
Individual imported symbols should be sorted alphabetically. The last symbol line should end with a comma.
Imports from packages and modules should be grouped in categories like
- Standard library packages
- 3rd-party packages
- DataLad core (absolute imports)
- DataLad extensions
- DataLad core (“local” relative imports)
Sorting imports can be aided by https://github.com/PyCQA/isort (e.g. python -m isort -m3 --fgw 2 --tc <filename>).

Examples

   from collections import OrderedDict
   import logging
   import os

   from datalad.utils import (
       bytes2human,
       ensure_list,
       ensure_unicode,
       get_dataset_root as gdr,
   )

In the `datalad/submodule/tests/test_mod.py` test file demonstrating an "exception" to absolute imports
rule where test files are accompanying corresponding files of the underlying module::

   import os

   from datalad.utils import ensure_list

   from ..mod import func1

   from datalad.tests.utils_pytest import assert_true