Develop Reference

How to import module installed by pip to a custom directory

I'm writing a plugin for an app, and found that packages I install with pip are apparently being ignored, so I'm trying to install them within my plugin's directory using
pip install --ignore-installed --install-option="--prefix=[plugins-folder]" [package-name]
This creates a folder structure lib/python2.7/site-packages/[dependencies] which is fine by me, except I can't figure out how to them import those dependencies. Even if I manage to import the main package, it will break because it can't find it's own dependencies which are also in that same directory structure.

I suggest that you should use virtual python environment. virtualenv for python2/python3 and python3 -m venv for python3.
You python environment seems orderless and you should isolate each environment for each python app.

What's the standard way to package a python project with dependencies?

I have a python project that has a few dependencies (defined under install_requires in setup.py). My ops people requires a package to be self contained and only depend on a python installation. The litmus test would be that they're able to get a zip-file and then unzip and run it without an internet connection.
Is there an easy way to package an install including dependencies? It is acceptable if I have to build on the OS/architecture that it will eventually be run on.
For what it's worth, I've tried both setup.py build and setup.py sdist, but they don't seem to fit the bill since they do not include dependencies. I've also considered virtualenv (which could be installed if absolutely necessary), but that has hard coded paths which makes it less than ideal.

There are a few nuances to how pip works. Unfortunately, using --prefix vendor to store all the dependencies of the project doesn't work if any of those dependencies, or dependencies of dependencies are installed into a place where pip can find them. It will skip those dependencies and just install the rest to your vendor folder.
In the past I've used virtualenv's --no-site-packages option to solve this issue. At one company we would ship the whole virtualenv, which includes the python binary. In the interest of only shipping the dependencies, you can combine using a virtualenv with the --prefix switch on pip to give yourself a clean environment that installs to the right place.
I'll provide an example script that creates a temporary virtualenv, activates it, then installs the dependencies to a local vendor folder. This is handy if you are running in CI.
#!/bin/bash
tempdir=$(mktemp -d -t project.XXX) # create a temporary directory
trap "rm -rf $tempdir" EXIT # ensure it is cleaned up
# create the virtualenv and exclude packages outside of it
virtualenv --python=$(which python2.7) --no-site-packages $tempdir/venv
# activate the virtualenv
source $tempdir/venv/bin/activate
# install the dependencies as above
pip install -r requirements.txt --prefix=vendor

In most cases you should be able to "vendor" all the dependencies. It's basically a crude version of virtualenv.
For example look at how the requests package includes chardet and urllib3 in its own source tree. Here's an example script that should do the initial downloading and copying for you: https://gist.github.com/proppy/1136723
Once you have the dependencies installed, you can reference them with from .some.namespace import dependency_name to make sure that you're using your local versions.

It's possible to do this with recent versions of pip (I'm using 8.1.2). On the build machine:
pip install -r requirements.txt --prefix vendor
Then run it:
PYTHONPATH=vendor/lib/python2.7/site-packages python yourapp.py
(This is basically an expansion of #valentjedi comment. Thanks!)

let's say you have python module app.py with dependencies in requirements.txt file.
first, install all your dependencies in appdeps folder.
python -m pip install -r requirements.txt --target=./appdeps
then in your app.py module add this dependency folder to the pythonpath
# app.py
import sys
sys.path.append('appdeps')
# rest of your module normally
#...
this will work the same way as if you were running this script from venv with all the dependencies installed inside ;>

When would the -e, --editable option be useful with pip install?

When would the -e, or --editable option be useful with pip install?
For some projects the last line in requirements.txt is -e .. What does it do exactly?

As the man page says it:
-e,--editable <path/url>
Install a project in editable mode (i.e. setuptools "develop mode") from a local project path or a VCS url.
So you would use this when trying to install a package locally, most often in the case when you are developing it on your system. It will just link the package to the original location, basically meaning any changes to the original package would reflect directly in your environment.
Some nuggets around the same here and here.
An example run can be:
pip install -e .
or
pip install -e ~/ultimate-utils/ultimate-utils-proj-src/
note the second is the full path to where the setup.py would be at.

Concrete example of using --editable in development
If you play with this test package as in:
cd ~
git clone https://github.com/cirosantilli/vcdvcd
cd vcdvcd
git checkout 5dd4205c37ed0244ecaf443d8106fadb2f9cfbb8
python -m pip install --editable . --user
it outputs:
Obtaining file:///home/ciro/bak/git/vcdvcd
Installing collected packages: vcdvcd
Attempting uninstall: vcdvcd
Found existing installation: vcdvcd 1.0.6
Can't uninstall 'vcdvcd'. No files were found to uninstall.
Running setup.py develop for vcdvcd
Successfully installed vcdvcd-1.0.6
The Can't uninstall 'vcdvcd' is normal: it tried to uninstall any existing vcdvcd to then replace them with the "symlink-like mechanism" that is produced in the following steps, but failed because there were no previous installations.
Then it generates a file:
~/.local/lib/python3.8/site-packages/vcdvcd.egg-link
which contains:
/home/ciro/vcdvcd
.
and acts as a "symlink" to the Python interpreter.
So now, if I make any changes to the git source code under /home/ciro/vcdvcd, it reflects automatically on importers who can from any directory do:
python -c 'import vcdvcd'
Note however that at my pip version at least, binary files installed with --editable, such as the vcdcat script provided by that package via scripts= on setup.py, do not get symlinked, just copied to:
~/.local/bin/vcdcat
just like for regular installs, and therefore updates to the git repository won't directly affect them.
By comparison, a regular non --editable install from the git source:
python -m pip uninstall vcdvcd
python -m pip install --user .
produces a copy of the installed files under:
~/.local/lib/python3.8/site-packages/vcdvcd
Uninstall of an editable package as done above requires a new enough pip as mentioned at: How to uninstall editable packages with pip (installed with -e)
Tested in Python 3.8, pip 20.0.2, Ubuntu 20.04.
Recommendation: develop directly in-tree whenever possible
The editable setup is useful when you are testing your patch to a package through another project.
If however you can fully test your change in-tree, just do that instead of generating an editable install which is more complex.
E.g., the vcdvcd package above is setup in a way that you can just cd into the source and do ./vcdcat without pip installing the package itself (in general, you might need to install dependencies from requirements.txt though), and the import vcdvcd that that executable does (or possibly your own custom test) just finds the package correctly in the same directory it lives in.

From Working in "development" mode:
Although not required, it’s common to locally install your project in
“editable” or “develop” mode while you’re working on it. This allows
your project to be both installed and editable in project form.
Assuming you’re in the root of your project directory, then run:
pip install -e .
Although somewhat cryptic, -e is short for
--editable, and . refers to the current working directory, so together, it means to install the current directory (i.e. your
project) in editable mode.
Some additional insights into the internals of setuptools and distutils from “Development Mode”:
Under normal circumstances, the distutils assume that you are going to
build a distribution of your project, not use it in its “raw” or
“unbuilt” form. If you were to use the distutils that way, you would
have to rebuild and reinstall your project every time you made a
change to it during development.
Another problem that sometimes comes up with the distutils is that you
may need to do development on two related projects at the same time.
You may need to put both projects’ packages in the same directory to
run them, but need to keep them separate for revision control
purposes. How can you do this?
Setuptools allows you to deploy your projects for use in a common
directory or staging area, but without copying any files. Thus, you
can edit each project’s code in its checkout directory, and only need
to run build commands when you change a project’s C extensions or
similarly compiled files. You can even deploy a project into another
project’s checkout directory, if that’s your preferred way of working
(as opposed to using a common independent staging area or the
site-packages directory).
To do this, use the setup.py develop command. It works very similarly
to setup.py install, except that it doesn’t actually install anything.
Instead, it creates a special .egg-link file in the deployment
directory, that links to your project’s source code. And, if your
deployment directory is Python’s site-packages directory, it will also
update the easy-install.pth file to include your project’s source
code, thereby making it available on sys.path for all programs using
that Python installation.

It is important to note that pip uninstall can not uninstall a module that has been installed with pip install -e. So if you go down this route, be prepared for things to get very messy if you ever need to uninstall. A partial solution is to (1) reinstall, keeping a record of files created, as in sudo python3 -m setup.py install --record installed_files.txt, and then (2) manually delete all the files listed, as in e.g. sudo rm -r /usr/local/lib/python3.7/dist-packages/tdc7201-0.1a2-py3.7.egg/ (for release 0.1a2 of module tdc7201). This does not 100% clean everything up however; even after you've done it, importing the (removed!) local library may succeed, and attempting to install the same version from a remote server may fail to do anything (because it thinks your (deleted!) local version is already up to date).

As suggested in previous answers, there is no symlinks that are getting created.
How does '-e' option work? -> It just updates the file "PYTHONDIR/site-packages/easy-install.pth" with the project path specified in the 'command pip install -e'.
So each time python search for a package it will check this directory as well => any changes to the files in this directory is instantly reflected.

Install local dist package into virtualenv

I have a pytest test, let's call it test.py. I used to run this test outside of virtualenv; now I'm trying to run it inside a virtualenv sandbox.
The project is structured like this:
~/project/test # where test.py and all virtualenv files live
~/project/mylibrary
test.py imports from mylibrary. In the past, this worked because I have the code in ~/project/mylibrary installed into /usr/lib/python2.7/dist-packages/mylibrary.
I can't run virtualenv with the --system-site-packages flag. I also can't move the code from ~/project/mylibrary into the ~/project/test folder. How can I get access to the code in mylibrary inside my virtualenv?

You don't need to do anything special - as long as you are working inside a virtualenv, python setup.py install will automatically install packages into
$VIRTUAL_ENV/lib/python2.7/site-packages
rather than your system-wide
/usr/lib/python2.7/dist-packages
directory.
In general it's better to use pip install mylibrary/, since this way you can neatly uninstall the package using pip uninstall mylibrary.
If you're installing a working copy of some code that you're developing, it might be a good idea to install it in "editable" mode using pip install -e mylibrary/, which creates a link to your source directory so that your installed module gets updated as you edit the code.

The easiest way would be to add the directory containing the library to your sys.path

Setup tools install command differences

What are the differences between the below commands
python setup.py install develop
Doesn't work for me error No such file or directory: 'build/bdist.macosx-10.7-intel/egg/test-easy-install-37886.pth'
python setup.py develop
Works for me appears to make an .egg link file
python setup.py install
Works for me appears to make a .egg file which in .zip file format

Develop is a setuptools / distribute feature that allows you to add a project
to your Python environment without installing it - so you can continue
its "development"
In other words, when you call "python setup.py develop", setuptools will
compile the metadata and hook your project into Python's site-package,
but the packages and modules that will be used are the one in the
directory where you've run that command.
This is useful to continue working on your code and testing it without
having to run "python setup.py install" on every run
With develop, Python 'pseudo-installs' a package by running the setup.py script instead of install. The difference is a modification of the environment (it doesn't with develop), so a package can be imported from it's current location instead of a site-package directory. The advantage of this is you can develop packages that are being used by other packages, and you can modify source code in place with develop.
As far as "setup.py install develop", I've never seen anyone use that before, sorry.
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python setup.py install develop
Is a wrong command.
When you use develop you use the current code when you run your application.
When you use install and then modify you code, your modifications will not be taken in account while running your app. until you rerun install or develop.