How to structure relative imports in Python 3.7?

Question

I've found myself in an import error situation I thought I was well past. I'm running Python 3.7.4 in VSCode on Windows 10. Without any further ado.. this is my folder and file structure, starting with folder crypto_code:

/crypto_code:

__init__.py (blank)

/crypto_driver:
    __init__.py (blank)
    crypto_balances.py

/crypto_exchg:
    __init__.py (blank)
    exchg_lens.py
    bittrex_lens.py
    coinbase_lens.py

Top of file coinbase_lens.py:

import exchg_lens

Top of file crypto_balances.py:

import sys
sys.path.append('..')
from crypto_exchg import coinbase_lens

Running coinbase_lens as main imports exchg_lens without error.

Running crypto_balances.py seems to recognize the paths/structure, but throws 'ModuleNotFoundError': No module named 'exchg_lens'.

Any help would be greatly appreciated. Thanks in advance.

Answer 1

This is an issue I've found troublesome as well. I have a setup that works and avoid messing with it. However this is good practice (for me) so ...

As a starting position I suggest abandoning import sys and sys.path.append. These are hacks that obscure the issue. If you use a linter (flake8 is what I use) then it will complain about sys.path.append appearing before imports and it is worth respecting what the linter dislikes.

I think the starting issue is, are you writing a module or a program. Restructuring your folders to provide a clear distinction.

/
program.py
/crypto
    __init__.py (empty)
    /driver
        __init__.py (empty)
        crypto_balances.py
    /exchg
        __init__.py (empty)
        coinbase_lens.py
        exchg_lens.py
    /test
        __init__.py (empty)
        test_coinbase_lens.py

program.py

from crypto.driver import crypto_balances
from crypto.exchg import coinbase_lens, exchg_lens

crypto_balances.py

from ..exchg import coinbase_lens
print('crypto_balances')

coinbase_lens.py

from . import exchg_lens
print('coinbase_lens')

exchg_lens.py

print('exchg_lens')

When run from the / folder produces

python .\program.py
exchg_lens
coinbase_lens
crypto_balances

Of course you should have a test framework to run tests on your module. The test file has the following content. Pytest sucessfully finds (and runs) the following test.

from crypto.exchg import coinbase_lens

def test():
    assert True

Later ... you can look at the package __init__.py and adding the imports and __all__ there to allow namespace management. Easy enough to add later.

Edited to add

Feels like I am missing a useful point that is worth including. \crypto\__init__.py and program.py can be altered to allow you to manage how the namespace of the module appears to the program.

__init__.py becomes

from crypto.driver import crypto_balances
from crypto.exchg import coinbase_lens, exchg_lens
__all__ = [
    "crypto_balances",
    "coinbase_lens", "exchg_lens"
]

program.py is now ...

from crypto import crypto_balances
from crypto import coinbase_lens, exchg_lens