Develop Reference

Python 3.6.5_1 installed in incorrect location (Mac OS)

I install python 3.6.5_1 using
brew install https://raw.githubusercontent.com/Homebrew/homebrew-core/f2a764ef944b1080be64bd88dca9a1d80130c558/Formula/python.r
and get
Warning: python 3.6.5_1 is already installed
The currently linked version is 3.7.3
You can use brew switch python 3.6.5_1 to link this version.
I use brew switch python 3.6.5_1 and get
Cleaning /usr/local/Cellar/python/3.6.5_1
Cleaning /usr/local/Cellar/python/3.7.3
4 links created for /usr/local/Cellar/python/3.6.5_1
Typing which python3, there is no output, which python gives
/usr/local/bin/python
and typing python3 gives
-bash: /usr/local/bin/python3: No such file or directory
typing python gives
Python 2.7.15 (default, Nov 27 2018, 21:24:58)
[GCC 4.2.1 Compatible Apple LLVM 10.0.0 (clang-1000.11.45.5)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
How do I make sure that the installed python3.6.5_1 is installed at correct location and is the one referred to by python3?
Extra background :
I have been working with OpenCV for around 5 months now, following this installation guide for installing all requirements including python3.6. I was using this version of brew's python instead of mac's one. Recently I had to install FFmpeg, some errors came up, unwittingly I did something (I don't remember, probably unlinked python) and then I wasn't able to install FFmpeg anyway but also this destroyed my workspace. Right now I keep getting the following error everytime I open up terminal:
-bash: /usr/local/bin/python3: No such file or directory
virtualenvwrapper.sh: There was a problem running the initialization hooks.
If Python could not import the module virtualenvwrapper.hook_loader,
check that virtualenvwrapper has been installed for
VIRTUALENVWRAPPER_PYTHON=/usr/local/bin/python3 and that PATH is
set properly.
I tried brew install python3 and that solves the above warning for virtualenvwrapper. But it installs python3.7.3, whereas I need python3.6 for tensor flow etc.

rpy2 module is invisible from python 2.7 on Mac 10.6.8

I am a bit of a noob on Mac and my python installation is refusing to acknowledge the existence of the rpy2 module on my mac. It looks like it only sees it as a Python 2.6 module. How do I make it visible in 2.7 ? Do I need to downgrade my python ? If so, how ? On the RPy2 web page (http://rpy.sourceforge.net/rpy2_download.html) Python 2.6 is recommended. Thanks!
mayumi#MAYUMI-iMac~:/ python --version
Python 2.7.6
mayumi#MAYUMI-iMac~:/ pip install rpy2
Requirement already satisfied (use --upgrade to upgrade): rpy2 in /Library/Python/2.6/site-packages/rpy2-2.3.8-py2.6-macosx-10.6-universal.egg
Cleaning up...
mayumi#MAYUMI-iMac~:/ python
Python 2.7.6 (v2.7.6:3a1db0d2747e, Nov 10 2013, 00:42:54)
[GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import rpy2
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ImportError: No module named rpy2
>>>

I also found it is difficult to successfully install rpy2 in OSX machines. Sometime it works, sometimes it doesn't, which is very annoying. I eventually settled with Anaconda Python distribution from https://store.continuum.io/cshop/anaconda/ to save all the troubles. Installing rpy2 never fails since the switch.
The default installation of Anaconda does not included rpy2, so you want to run the installation command, from Anaconda folder, bin subfolder
conda install rpy2
Depends on the version, you may get a bunch of warnings. Just ignore them.
Then rpy2 just works! Of course, only under the Anaconda python, not the other python version you may have installed on your machine.
You can run a few test to make sure rpy2 works, following this example: http://nbviewer.ipython.org/urls/raw.github.com/ipython/ipython/3607712653c66d63e0d7f13f073bde8c0f209ba8/docs/examples/notebooks/rmagic_extension.ipynb
bash commands, run in the folder /Users/YOUR_USER_NAME/anaconda/bin/:
user-Mac-Pro:bin user$ conda install rpy2
and it says:
Conda package not available for rpy2, attempting to install via pip
Downloading/unpacking rpy2
Downloading rpy2-2.3.8.tar.gz (185kB): 185kB downloaded
Running setup.py egg_info for package rpy2
If you don't have R installed it will complain with a few warnings and fetch R for you. Then there may be some other depreciation warnings dependents on what you have installed.
(I am not associated with Continuum in any way)

You can see that pip installed to the site-packages to python 2.6 since you installed pip with python 2.6 it will default to use that library.
rpy2 in /Library/Python/**2.6**/site-packages/rpy2-2.3.8-py2.6-macosx-10.6-universal.egg
You can redirect pip installation location or use easy_install2.7 which should be around in /usr/local/bin/

Install python module to non default version of python using .sh

I have a problem similar to this post: Install python module to non default version of python on Mac, so I am aware of those solutions, but they do not work for me.
I am installing M2Crypto on CentOS, which means I much use fedora_setup.sh build followed by fedora_setup.sh install in order to install on my architecture.
Unfortunately, the default Python version is 2.6, but I use 2.7. How do I execute the build and install commands so that they build and install to Python2.7 site-packages? Is there a simple command I don't know? I've been searching around here: http://docs.python.org/2/install/ in the Python Docs, but I don't see anything about .sh scripts?

You should run your scripts in a virtualenv created for your app's environment. This creates an isolated environment that uses the Python interpreter you created the virtualenv with, but with its own set of libraries.
# create the virtualenv folder: M2Crypto-venv
python2.7 virtualenv.py --distribute M2Crypto-venv
# activate the virtualenv, changing environment variables to use its Python interpreter
. M2Crypto-venv/bin/activate
# see how the current python has changed
which python # should be M2Crypto-venv/bin/python
python --version # should be 2.7
# after activating, run your install scripts
If you're using mod_wsgi or something similar to serve content, you'll want to modify your WSGI file to activate the virtualenv before doing anything else (adapted from mod_wsgi instructions):
import os.path
virtualenv_path = '/path/to/M2Crypto-venv'
activate_this = os.path.join(virtualenv_path, 'bin/activate_this.py')
execfile(activate_this, dict(__file__ = activate_this))
# rest of the WSGI file...

This was an incredibly difficult answer to come by, but the support team at Webfaction where I am hosted were spectacular in assisting me. Directly from the support I was given:
First build swig,
wget http://prdownloads.sourceforge.net/swig/swig-2.0.8.tar.gz
tar -xf swig-2.0.8.tar.gz
cd swig-2.0.8
./configure --prefix=$HOME
make
make install
Than get m2crypto,
svn checkout http://svn.osafoundation.org/m2crypto/tags/0.21/ m2crypto-0.21
cd m2crypto-0.21/
Edit fedora_setup.sh from this
SWIG_FEATURES=-cpperraswarn python setup.py $*
to this,
SWIG_FEATURES=-cpperraswarn python2.7 setup.py $*
Then build, then install,
./fedora_setup.sh build
./fedora_setup.sh install --prefix=$HOME
[me#web342 lib]$ python2.7
Python 2.7.5 (default, May 16 2013, 20:16:09)
[GCC 4.4.7 20120313 (Red Hat 4.4.7-3)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import M2Crypto
>>> print M2Crypto
<module 'M2Crypto' from '/home/me/lib/python2.7/site-packages/M2Crypto-0.21-py2.7-linux-x86_64.egg/M2Crypto/__init__.pyc'>
Obviously, substitute your own details throughout. Hope this helps the next guy trying to install M2Crytpo using fedora_setup to a non-default python version.

Installing Pygame for Python 3.1.2 in Ubuntu

I'm reading the book Introduction to Computer Science Using Python and Pygame by Paul Craven (note: legally available for free online). In the book, he uses a combination of Python 3.1.3 and Pygame 1.9.1 . In my Linux Ubuntu machine, I have Python 3.1.2 but even after I sudo apt-get installed python-pygame (version 1.9.1), Python 3.1.2 can't import pygame.
Python 3.1.2 (r312:79147, Sep 27 2010, 09:45:41)
[GCC 4.4.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import pygame
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ImportError: No module named pygame
Python 2.6.5 imports it without fuss, however,
Python 2.6.5 (r265:79063, Apr 16 2010, 13:09:56)
[GCC 4.4.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import pygame
>>>
Are you aware of any issues for Linux/Ubuntu's Python 3.1.2 (Prof. Craven used Windows in his book)? How come Pygame 1.9.1 worked for Python 3.1.3 but not for 3.1.2?
Thanks for any pointers. (--,)

PyGame on Python 3 remains experimental, but these steps worked for me on Ubuntu 11.10:
sudo apt-get install mercurial python3-dev libjpeg-dev libpng12-dev libportmidi-dev libsdl-image1.2-dev libsdl-mixer1.2-dev libsdl-ttf2.0-dev libsdl1.2-dev libsmpeg-dev libx11-dev ttf-freefont libavformat-dev libswscale-dev
hg clone -u 01b2cb16dc17 https://bitbucket.org/pygame/pygame
cd pygame
python3 config.py
2to3 setup.py -w
python3 setup.py build
sudo python3 setup.py install
(You may remove the -u 01b2cb16dc17 to try the latest version; 01b2cb16dc17 worked for me.)

I hate to re-open an old post, but I had the hardest time installing pygame with a version of python that was not Ubuntu's default build. So I created this tutorial/ how to:
Install python3.1 and pygame1.9.1 in Ubuntu
I hopes this helps the next unfortunate soul to try this.

I installed pygame for python3 quite easily using the pip3 (a tool for installing and managing Python packages) command on Ubuntu 16.04.7 LTS.
Open a terminal and install pip3, type sudo apt install python3-pip
Now use it to install pygame for python3, type pip3 install pygame
That's it! Import the library and confirm that everything works:
# I'll try it out using the python 3 interpreter.
python3 --version
Python 3.5.2
robert#robert-E7212:~/Source/Python/python_crash_course/alien_invasion$ python3
Python 3.5.2 (default, Oct 7 2020, 17:19:02)
[GCC 5.4.0 20160609] on linux
Type "help", "copyright", "credits" or "license" for more information.
# No errors, pygame was imported successfully!
>>> import pygame
pygame 2.0.0 (SDL 2.0.12, python 3.5.2)
Hello from the pygame community. https://www.pygame.org/contribute.html
>>>

I followed #Søren 's method, but without the -u number.
The only complication was a few compilation errors at the last line, all due to syntax and unicode differences between Python 2 and Python 3, but with a little checking of the web documentation it was a matter of a few minutes with a text editor modifying the following files (all paths are relative to the pygame directory created during the download):
gedit build/lib.linux-x86_64-3.2/pygame/colordict.py
gedit build/lib.linux-x86_64-3.2/pygame/tests/test-utils/png.py
gedit build/lib.linux-x86_64-3.2/pygame/examples/movieplayer.py
The line numbers from the compiler error messages are great for giving you where to start. The things to look out for are:
1 remove all references to u"xxxx" colours
2 use Python3 syntax for exceptions
3 change all print commands to Python3 equivalents
Then re-issue the final compilation command:
sudo python3 setup.py install
If you miss one or two or get it wrong, just keep going round the loop editing and re-compiling till it works.
BTW I deliberately did not give details of the compiler messages, because I expect they will depend on the current build you download. The files I needed to change were for version '1.9.2pre' downloaded as of the date on this post.

Just use the below command to install pygame for Python3. I could install pygame correctly on Ubuntu 16.04 and Python Python 3.5.2.
pip3 install pygame

It's because installing the python-pygame package installs it for the default version of Python on your system, 2.6.5 in this case. You should download the pygame package and use setup.py to install it in 3.1.2.

The python-pygame package is only compiled for python2.6 and python2.7 where I am. You'll have to install it again, possibly from a python3 branch of the source.

opencv python osx

(Step 1)
I'm trying to get openCV to run from python on my mac using the MacPorts install http://opencv.willowgarage.com/wiki/Mac_OS_X_OpenCV_Port, and also trying to follow The Petite Geek's guide:
sudo port -v install opencv +python26
It runs for about 10 minutes without errors.
(Step 2)
I download ctypes-opencv source and demo files. I navigate to the src directory and run:
sudo python setup.py install
I see like 50 lines almost all of the form: copying ... -> ..., which looks good to me. No errors here.
(Step 3)
I add export DYLD_FALLBACK_LIBRARY_PATH=/opt/local/lib to the end of my ~/.profile.
(Step 4)
I open a new terminal to test my install. From my home folder:
$ python
Python 2.6.2 (r262:71600, Apr 16 2009, 09:17:39)
[GCC 4.0.1 (Apple Computer, Inc. build 5250)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import cv
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ImportError: No module named cv
>>>
Does not work.
I read somewhere that opencv installs python bindings with the default version of python for OSX, and I am probably running a non-default version, but this is not actionable information to me.

I struggled for a while with Python on Mac. Here is how I finally (and easily!) installed it. Remove all the things Python you have on there already. They will probably be located at /Library/Frameworks/Python.Framework and /opt/local/var/macports/software/py26*
First download Python with Macports.
sudo port install python27
Then make sure your system is using this version with:
sudo port select --set python python27
Next install numpy with:
sudo port install py27-numpy
Now install opencv:
sudo port install opencv +python27
Now edit your ~/.bash_profile with:
sudo /Applications/TextEdit.app/Contents/MacOS/TextEdit ~/.bash_profile
or
open -t ~/.bash_profile
and add the line:
export PYTHONPATH=/opt/local/var/macports/software/opencv/2.2.0_0+python27/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages:$PYTHONPATH
or where ever your version of the cv.so file is hidden....
Now restart terminal and try:
%python
>>>import cv
I'm using Netbeans for opencv and python and it works really nice. Good luck.

$ brew search opencv
homebrew/science/opencv
$ brew install homebrew/science/opencv
after installed, there is warning:
==> Caveats
If you need Python to find the installed site-packages:
mkdir -p ~/Library/Python/2.7/lib/python/site-packages
echo '/usr/local/lib/python2.7/site-packages' > ~/Library/Python/2.7/lib/python/site-packages/homebrew.pth
so, just do
mkdir -p ~/Library/Python/2.7/lib/python/site-packages
echo '/usr/local/lib/python2.7/site-packages' > ~/Library/Python/2.7/lib/python/site-packages/homebrew.pth

If you notice the first line output when running python, you'll see that you're still using the Apple-supplied Python interpreter. Try installing and using the python-select package in MacPorts and then try the instructions again starting from step 2.
Also make sure you followed all of the steps when installing MacPorts so that /usr/local/bin is on $PATH.

Another "hack" I found during my struggles using CMake (but maybe the problem is the same with ports) : it appears that the python modules location has been duplicated on my Mac OS Lion, for a reason I can't explain.
CMake wants to put the "cv" module here :
/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages
Whereas my default Python interpreter is looking here (thanks PyCharm for telling me) :
/Library/Python/2.7/site-packages
Moving both cv2.so and cv.py files to the second location, did the trick for me. I don't know if this is the cleanest way.
Hope it can help some googlers !