# Which is the right way to use modules within a package? **URL:** \ **Category:** Packaging\ **Created:** [April 26, 2022, 2:05pm UTC](https://discuss.python.org/t/which-is-the-right-way-to-use-modules-within-a-package/15297 "2022-04-26T14:05:40Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![gloriamacia](https://sea2.discourse-cdn.com/flex002/user_avatar/discuss.python.org/gloriamacia/32/3251_2.png) [@gloriamacia](https://discuss.python.org/u/gloriamacia)\ **Post date:** [April 26, 2022, 2:05pm UTC](https://discuss.python.org/t/which-is-the-right-way-to-use-modules-within-a-package/15297/1 "2022-04-26T14:05:40Z")
Trying to understand the following which is always giving me trouble - Let’s say, I have a minimalistic python package that looks as follows: ```auto maciamug@maciamug-PNMD6V mygalaxy % tree . . ├── README.md ├── poetry.lock ├── pyproject.toml ├── src │ └── mygalaxy │ ├── __init__.py │ ├── calc.py │ └── planet.py ``` `planet.py` uses `calc.py` module, I am importing it as follows: `from mygalaxy.calc import planet_mass, planet_vol` This works just fine (trial and error). What I wonder is, why was the following ways not working: ```auto from calc import planet_mass, planet_vol ``` or else ```auto from .calc import planet_mass, planet_vol ``` ---
**Author:** ![abravalheri](https://sea2.discourse-cdn.com/flex002/user_avatar/discuss.python.org/abravalheri/32/4990_2.png) [@abravalheri](https://discuss.python.org/u/abravalheri)\ **Post date:** [April 26, 2022, 5:42pm UTC](https://discuss.python.org/t/which-is-the-right-way-to-use-modules-within-a-package/15297/2 "2022-04-26T17:42:44Z")
Hi Gloria, the import system in Python evolved quite a bit since its first implementation, so right now we have 2 (main) ways of writing an import: 1. _ **absolute imports** _: this corresponds to your first example (`from mygalaxy.calc import ...`) When using this syntax you need to write the whole path to your package/module. 2. _ **explicit relative imports** _: this corresponds to your last example (`from .calc import ...`) When using this syntax you need to pay attention to the location of the file **where you are writing the import statement**. `from .calc import ...` means that the `calc` module is a sibling of the module you are writting, i.e. it is located inside the same folder. This should also work depending on how you are calling your Python scripts. If it is not working probably there is some detail in your development environment that is not quite right… For example, you might need to run `pip install .`/`pip install -e .` (or set `PYTHONPATH` accordingly) to make the package under development available to your tests. There is a nice article about this in [Absolute vs Relative Imports in Python – Real Python](https://realpython.com/absolute-vs-relative-python-imports/). The statement `from calc import ...` will not work because it tries to use an _ **implicit relative import** _ which is no longer supported by Python (it was removed for being ambiguous and the cause of common problems). ---
**Author:** ![cameron](https://sea2.discourse-cdn.com/flex002/user_avatar/discuss.python.org/cameron/32/2658_2.png) [@cameron](https://discuss.python.org/u/cameron)\ **Post date:** [April 26, 2022, 9:53pm UTC](https://discuss.python.org/t/which-is-the-right-way-to-use-modules-within-a-package/15297/3 "2022-04-26T21:53:20Z")
By Gloria Macia via Discussions on [Python.org](http://Python.org) at 26Apr2022 14:15: > Trying to understand the following which is always giving me trouble - > Let’s say, I have a minimalistic python package that looks as follows: > > ```auto > maciamug@maciamug-PNMD6V mygalaxy % tree . > . > ├── README.md > ├── poetry.lock > ├── pyproject.toml > ├── src > │ └── mygalaxy > │ ├── __init__.py > │ ├── calc.py > │ └── planet.py > > ``` > > `planet.py` uses `calc.py` module, I am importing it as follows: > > `from mygalaxy.calc import planet_mass, planet_vol` > > This works just fine (trial and error). What I wonder is, why was the following ways not working: That’s a normal “absolute” import, where the module name has a path from the top of the tree. It presumes that “src” is in your `syspath` list. > ```auto > from calc import planet_mass, planet_vol > > ``` This is an absolute import, and the path is wrong (“calc” is not at the top of the tree). > or else > > ```auto > from .calc import planet_mass, planet_vol > > ``` I’d expect this to work. Can you shows the full error traceback? Also your `sys.path` (inside Python: `import sys; print(sys.path)` and/or `$PYTHONPATH` environment variable. It may matter how you invoked things. Are you: - invoking something else which imports from `mygalaxy` etc, and finds it with `sys.path` - invoking `planet.py` directly? (in which case I would not expect `from mygalaxy.calc` to work) Can you show the invocation command (how you start Python to test these)? My personal habit would be to either (a) install the `mygalaxy` package using `pip` or (b) add `/path/to/src` to my `$PYTHONPATH` environment variable. I’d hope to use this form: ``` from .calc import planet_mass, planet_vol ``` because `planet.py` knows that `calc.py` is part of its own package, and this avoids needing to know the absolute name of the package. If `planet.py` was found by an import, then it knows it is in a package. If you invoke `planet.py` _directly_, I believe it does not consider it part of a package, and therefore the relative import path `.calc` would not work. So a script `foo.py` which goes: ``` from mygalaxy.planet import something ``` would let `planet.py` get to `.cacl`. Cheers, Cameron Simpson [cs@cskk.id.au](mailto:cs@cskk.id.au) ---
**Author:** ![gloriamacia](https://sea2.discourse-cdn.com/flex002/user_avatar/discuss.python.org/gloriamacia/32/3251_2.png) [@gloriamacia](https://discuss.python.org/u/gloriamacia)\ **Post date:** [April 27, 2022, 12:30pm UTC](https://discuss.python.org/t/which-is-the-right-way-to-use-modules-within-a-package/15297/4 "2022-04-27T12:30:59Z")
@abravalheri you were right. Absolute import work, explicit relative import works - implicit relative import fails. I am running on poetry and it was needed to do “poetry install” to update the version of my package in the poetry virtual environment. ---
**Author:** ![gloriamacia](https://sea2.discourse-cdn.com/flex002/user_avatar/discuss.python.org/gloriamacia/32/3251_2.png) [@gloriamacia](https://discuss.python.org/u/gloriamacia)\ **Post date:** [April 27, 2022, 12:49pm UTC](https://discuss.python.org/t/which-is-the-right-way-to-use-modules-within-a-package/15297/5 "2022-04-27T12:49:23Z")
Very interesting @cameron This is my `print(sys.path)` output `['', '/usr/local/Cellar/python@3.9/3.9.7/Frameworks/Python.framework/Versions/3.9/lib/python39.zip', '/usr/local/Cellar/python@3.9/3.9.7/Frameworks/Python.framework/Versions/3.9/lib/python3.9', '/usr/local/Cellar/python@3.9/3.9.7/Frameworks/Python.framework/Versions/3.9/lib/python3.9/lib-dynload', '/Users/maciamug/Library/Caches/pypoetry/virtualenvs/mygalaxy-dawQFL-m-py3.9/lib/python3.9/site-packages', '/Users/maciamug/Desktop/repos/mygalaxy/src']` So if I understood you here correctly (please bear in mind with me, a package beginner): ```auto from calc import planet_mass, planet_vol ``` > That’s a normal “absolute” import, where the module name has a path from > the top of the tree. It presumes that “src” is in your `syspath` list. > type or paste code here Does not work because it would expext “calc.py” to be at the same level as “src”. I moved calc.py at the source level like this: ```auto maciamug@maciamug-PNMD6V mygalaxy % tree . . ├── README.md ├── calc.py ├── poetry.lock ├── pyproject.toml ├── src │ └── mygalaxy │ ├── __init__.py │ └── planet.py ``` And after `poetry install` to update the package it worked! My only question remaining is, when I run `poetry build` I see only files inside` src` are taking. In other words, only files inside `src` folder get uploaded to PyPi which I guess it means that someone trying to download from there this package would get something broken `(calc.py` missing as shown below). Is this correct? ```auto maciamug@maciamug-PNMD6V dist % tree mygalaxy-0.1.3 mygalaxy-0.1.3 ├── PKG-INFO ├── README.md ├── pyproject.toml ├── setup.py └── src └── mygalaxy ├── __init__.py └── planet.py ``` So in practice then this is not a great way to import and I should rather use absolute or explicit relative imports. > ```auto > from calc import planet_mass, planet_vol > > ``` Thanks a lot for your guidance, much appreciated as I learned a lot from you. ---
**Author:** ![CAM-Gerlach](https://sea2.discourse-cdn.com/flex002/user_avatar/discuss.python.org/cam-gerlach/32/3688_2.png) [@CAM-Gerlach](https://discuss.python.org/u/CAM-Gerlach)\ **Post date:** [May 5, 2022, 6:59pm UTC](https://discuss.python.org/t/which-is-the-right-way-to-use-modules-within-a-package/15297/6 "2022-05-05T18:59:33Z")
> [@gloriamacia](#): > > Does not work because it would expext “calc.py” to be at the same level as “src”. Not quite; what @cameron means is that it presumes `calc.py` is a top-level module inside your `src` directory, from which it is presumed that your modules/`import packages` are installed or is visible to Python (via one of many possible ways). I.e. ```auto ├── README.md ├── poetry.lock ├── pyproject.toml ├── src │ |── calc.py py │ └── mygalaxy │ ├── __init__.py │ └── planet.py ``` But this is presumably _not_ what you want to do, as long as you want `calc` to be part of your `mygalaxy` import package as opposed to a totally separate module. > [@gloriamacia](#): > > I moved calc.py at the source level like this: This is most certainly **not** what you want to do. Since it is outside your import package and outside your installed package directory, if it still works to import it, it only does so purely by accident (e.g. `mygalaxy-0.1.3` happens to be your current working directory, and your particular method of starting Python puts the CWD on the module search path). It will _not_ work for anyone else who installs and tries to use your package (as you indeed discovered), or if that isn’t your CWD (or otherwise on your path), or invoking it in a way that doesn’t have your CWD on your path, or… It also means that the local copy of `code` can be picked up by the installed copy of your package, which can lead to all sorts of unexpected behavior. In short, please _do not_ ever do this. Instead, if you want to use a relative import, simply be explicit and prefix `code` with `.`—as indeed, it seems you figured out on your own. Best of luck!