Python "setup.py develop": is it possible to create ".egg-info" folder not in source code folder?
Python has ability to "pseudoinstall" a package by running it's setup.py script with develop instead of install. This modifies python environment so package can be imported from it's current location (it's not copied into site-package directory). This allows to develop packages that are used by other packages: source code is modified in place and changes are available to rest of python code via simple import.
All works fine except that setup.py develop command creates an .egg-info folder with metadata at same level as setup.py. Mixing source code and temporary files is not very good idea - this folder need to be added into "ignore" lists of multiple tools starting from vcs and ending backup systems.
Is it possible to use setup.py develop but create .egg-info directory in some other place, so original source code is not polluted by temporary directory and files?
Answer
setup.py develop creates a python egg, in-place; it does not [modify the] python environment so package can be imported from it's current location. You still have to either add it's location to the python search path or use the directory it is placed in as the current directory.
It is the job of the develop command to create an in-place egg, which may include compiling C extensions, running the 2to3 python conversion process to create Python3 compatible code, and to provide metadata other python code may be relying on. When you install the package as an egg in your site-packages directory, the same metadata is included there as well. The data is certainly not temporary (it is extracted from your setup.py file for easy parsing by other tools).
The intent is that you can then rely on that metadata when using your package in a wider system that relies on the metadata being present, while still developing the package. For example, in a buildout development deployment, we often use mr.developer to automate the process of fetching the source code for a given package when we need to work on it, which builds it as a develop egg and ties it into the deployment while we work on the code.
Note that the .egg-info directory serves a specific purpose: to signal to other tools in the setuptools eco-system that your package is installed and available. If your package is a dependency of another egg in your setup, then that dependency is satisfied. pip and easy_install and buildout will not try and fetch the egg from somewhere else instead.
Apart from creating the .egg-info directory, the only other thing the command does, is to build extensions, in-place. So the command you are looking for instead is:
setup.py build_ext --inplace
This will do the exact same thing as setup.py develop but leave out the .egg-info directory. It also won't generate the .pth file.
There is no way of generating only the .pth file and leave out the .egg-info directory generation.
Technically speaking, setup.py develop will also check if you have the setuptools site.py file installed to support namespaced packages, but that's not relevant here.