Develop Reference

How to download python library in a separate folder?

I want to download python libraries like NumPy, scipy, etc. in a separate folder. I want to include that folder in the python project so that whenever I switch to some other laptop, I don't need to install the libraries again rather I import libraries from that folder. Is there any way?

You can easily install python virtualenv.
Your libraries will be installed in directory created by virtualenv.
https://pypi.org/project/virtualenv/.
Other option, you can also use docker.

I suggest using virtual environment in this case. You could use pipenv so that the project hast exactly the libraries you need for it to run.

You can do it.
for numpy library: https://pypi.org/project/numpy/#files
You can download the files statically from pypi.
I would not recommend you go with this approach. There are several reasons to do that.
There would be a dependency on this kind of library. So you have to keep these dependencies along with the NumPy package.
These libraries are getting updated after some time with some newly added functionality and some bug fixes. So with the time other libraries might not compatible with this library.
Recommended way:
Just create an requirement.txt file that contains all the dependency with its version number.
whenever you want to use your project elsewhere, just install all these libraries with below command.
pip install -r requirement.txt

There are two major way you can install python libs to a separate folder: a virtual environment or a container.
Virtula environment (like venv, pipenv, etc) is good as this is the simplest way to your project's own liblaries set which is not impact any other pythonic script in your system. The downside of this case is thet you really have to set up an environment (including lib install) on every computer you move your script to. This can and should be autimated, of course, but this should be done either way.
The container, in other hand, requires additional resources to handle and to build, build, but it is exactly the box with a specific version of your script along with all libs and binaries it requires. No need to reinstall libs while moving to new laptop/desktop/server/cloud/whatever. For this case I would recommend the Docker/Kubernetes. But it's better to start with Docker.

Install python package into directory relative to site-packages

I have a Python package that is one of a collection of company Python packages. When I run
python setup.py install
I want the package to be installed to a common company directory, along with other company packages. I want this directory to be relative to the default Python install directory, e.g.,
/usr/lib/python2.7/site-packages/<company_name>/<python_package_name>
That is, I want to insert <company_name> into the installation path at install time.
I've seen ways to prefix this path, but can't seem to work out how to do what I've described.

Unfortunately Python packaging doesn't work like that. You could probably bend it to work like that but that would be quite an effort for a person without experience in Python packaging and even for experienced persons the amount/output tradeoff would not make sense. You do not mention any motive to do this besides your personal preference.
Instead, to have well-managed and human-navigable package installation folder, I recommend you to study the following resources
PEP 0382 - Namespace Packages: How to create packages like companyname.foobar, companyname.moomoo
Installing packages into a virtualenv - Python packaging installation guide (official)
Scrambler: Symlink namespaced Python packages to a single folder

Python setup.py develop vs install

Two options in setup.py develop and install are confusing me. According to this site, using develop creates a special link to site-packages directory.
People have suggested that I use python setup.py install for a fresh installation and python setup.py develop after any changes have been made to the setup file.
Can anyone shed some light on the usage of these commands?

python setup.py install is used to install (typically third party) packages that you're not going to develop/modify/debug yourself.
For your own stuff, you want to first install your package and then be able to frequently edit the code without having to re-install the package every time — and that is exactly what python setup.py develop does: it installs the package (typically just a source folder) in a way that allows you to conveniently edit your code after it’s installed to the (virtual) environment, and have the changes take effect immediately.
Note: It is highly recommended to use pip install . (regular install) and pip install -e . (developer install) to install packages, as invoking setup.py directly will do the wrong things for many dependencies, such as pull prereleases and incompatible package versions, or make the package hard to uninstall with pip.
Update:
The develop counterpart for the latest python -m build approach is as follows (as per):

From the documentation. The develop will not install the package but it will create a .egg-link in the deployment directory back to the project source code directory.
So it's like installing but instead of copying to the site-packages it adds a symbolic link (the .egg-link acts as a multiplatform symbolic link).
That way you can edit the source code and see the changes directly without having to reinstall every time that you make a little change. This is useful when you are the developer of that project hence the name develop. If you are just installing someone else's package you should use install

Another thing that people may find useful when using the develop method is the --user option to install without sudo. Ex:
python setup.py develop --user
instead of
sudo python setup.py develop

Cleaning Python modules an have fresh start Mac OS X

I am not a total newbie but I am trying to install modules for quite a long time and at this point i would like to have a fresh start and install python and all the modules I need so i really understand them. My problem is that some of them import, but most of them install either to the wrong site-packages or dont import maybe because i messed up my system/python. Also I tried the PYTHONPATH and PATH to set this up right, but it never worked.
So my questions are:
Is there a way to ensure I can clean everything up and start from zero ?
Ideally this would be without having to set up Mac OSX new.
Is there a way to install all the modules in the correct place (whatever the directory is I dont care, it should just work)?
Is there a good step-by-step description on how installing modules works. And I dont mean just the info to use easy_install, pip install etc, but a way to fully understand what I need to consider, where I need to put them, why these modules are recognized in certain directories, how the system finds them and most important what are the most common pitfalls and how to avoid them.
I also tried Macports and various other similiar ways to install but even if some of them worked and while I am sure that these are really great tools, most I had to hack to work.
So if someone can recommend a good and stable way to install a lot of modules at once, this would be incredibly useful.
Thanks a lot !!!!
And sorry for the long questions.

Buildout and virtualenv should be what you are looking for.
Buildout helps you configure a python installation and virtualenv allows you to isolate multiple different configurations from each other.
Here's a nice blog post explaining how to use them together.
Also, see this other question: Buildout and Virtualenv

You can safely install an up-to-date Python 2 and/or Python 3 on OS X using the python.org installers here. They will coexist with any other Pythons you have installed or that were shipped by Apple with OS X. To install packages, for each Python instance first install Distribute which will install a version-specific easy_install command, i.e. easy_install-2.7 or easy_install-3.2. Many people prefer to use pip to manage packages; you can use easy_install to install a version-specific copy of it. If you want something fancier, you could also install virtualenv but, with the isolation provided by Python framework builds on OS X, that isn't as necessary as on most other platforms.

Is there a way to install all the modules in the correct place?
Download and untar/gunzip/etc the module source (Most of the modules ares available in gzip form at http://pypi.python.org/pypi), then run configure with --prefix set to the same thing for every install:
[ 11:06 jon#hozbox.com ~ ]$ ./configure --prefix=/usr/local
/usr/local is usually the default, but it doesn't hurt to specify it and will ensure that every module you install will be placed in /usr/local/lib/python/...
Is there a good step-by-step description on how installing modules works?
The Python website has a great page called: Installing Python Modules
http://pypi.python.org/pypi
http://docs.python.org/install/index.html

How can I use pywin32 with a virtualenv without having to include the host environment's site-packages folder?

I'm working with PyInstaller under Python 2.6, which is only partially supported due to the mess MS have created with their manifest nonense which now affects Python since it is now MSVC8 compiled.
The problem is that the manifest embedding support relies on the pywin32 extensions in order to build which is a pain because without including the host's site-packages folder when I create the virtualenv (kinda defeats the point in a build environment) I cannot find a way to install the required extensions so they are accessible to PyInstaller.
Has anyone found a solution to this issue?

I found http://old.nabble.com/Windows:-virtualenv-and-pywin32--td27658201.html (now a dead link) which offered the following solution:
Browse http://sourceforge.net/projects/pywin32/files/ for the URL of the exe you want
Activate your virtualenv
Run easy_install http://PATH.TO/EXE/DOWNLOAD
This works with modern versions of setuptools (circa February 2014, reported by tovmeod in the comments).
If you are using an old version of setuptools (or distribute it merged back into setuptools), you may get this error message:
error: c:\users\blah\appdata\local\temp\easy_install-ibkzv7\pywin32-214.win32-py2.6.exe is not a valid distutils Windows .exe
In which case:
Download the exe yourself
Activate your virtualenv
Run easy_install DOWNLOADED_FILE.exe
I rather hopefully tried "pip install" rather than "easy_install", but this didn't work, and likely never will (citation needed).
Finally, I found but haven't tested a solution at http://www.mail-archive.com/python-list#python.org/msg272040.html which is:
Solved this by copying the pywin32.pth file into my virtualenv site-packages
and editing the file to point to the path.
If the other options don't work for you, maybe this will?

For Python 2.7 or 3.x use pypiwin32.
pip install pypiwin32

OK, well since I had to find a way forward I improvised. I've internally created a git repository with a hacked-together version of pywin32 that will install within a virtualenv using the standard setup.py script. It took a lot of fiddling to make it work right but I managed to get it to load and the dependent code now works as I need it to. If people feel this would be of benefit to the community please post a comment: if I get enough I'll try and put something up on my github account.

This may have been improved since previous answer, since I've successfully installed pywin32 on sandbox on several machines without any specific "hacks" :
$ virtualenv sandbox
$ sandbox\scripts\activate
(sandbox) $ git clone https://github.com/Travis-Sun/pywin32.git
(sandbox) $ cd pywin32
(sandbox) $ python setup.py install
Tested with following environment :
windows 7
git
python 2.7.10 with virtualenv
VS2008. It may also work (but I've not tested yet) with
http://www.microsoft.com/en-us/download/details.aspx?id=44266

Edit: Scratch this for now, appears to be some problems with the installation still...
I got rather tired of the whole situation, and just created a set of converted wheels ("wheel convert <.exe>"). I'll try and keep them maintained for the most recent build, but do shout if there are any issues.
https://tr00st.co.uk/python/wheel/pywin32/
Installation can be done easily using pip and pointing to the package matching your version and architecture. For example, for Python 3.5/amd64:
pip install https://tr00st.co.uk/python/wheel/pywin32/pywin32-219-cp35-none-win_amd64.whl
Caveat: The --upgrade process currently fails, as the uninstall procedure is unable to clean up after itself (Access Denied when cleaning up win32api.pyd) - this is only when removing the temporary directory, which can be manually deleted. Easiest way around this is to uninstall and reinstall instead of upgrading, then manually delete the temporary folder.