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.

ImportError: Twisted requires zope.interface 3.6.0 or later: actually it have been installed

I use OSX 10.9 + Kivy 1.9.1, but I have two versions of Python, Mac OSX self-contained 2.7.5 and another standalone 2.7.9 installed. Here are the details:
MacBook-Air:wzy$ python
Python 2.7.5 (default, Mar 9 2014, 22:15:05)
[GCC 4.2.1 Compatible Apple LLVM 5.0 (clang-500.0.68)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
MacBook-Air:wzy$ python
Python 2.7.9 (v2.7.9:648dcafa7e5f, Dec 10 2014, 10:10:46)
[GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
After having installed twisted with pip install twisted, I get the following error message in kivy with python 2.7.5, which does not happen in python 2.7.9
MacBook-Air:wzy$ kivy
>>> import twisted
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/twisted/__init__.py", line 53, in <module>
_checkRequirements()
File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/twisted/__init__.py", line 37, in _checkRequirements
raise ImportError(required + ": no module named zope.interface.")
ImportError: Twisted requires zope.interface 3.6.0 or later: no module named zope.interface.
MacBook-Air:wzy$ python
>>> import twisted
>>> exit()
I have even installed zope.interface several times and dedicate install target directory as one of the sys.path of kivy environment.
I do believe this is two version co-exist related, but how can I fix this?

When you do pip install twisted, you are installing Twisted into some Python environment, depending on which python executable you are invoking pip with. If you have a 2.7.5 environment and a 2.7.9 environment, pip install might be putting Twisted in a different place for each, depending on what other options you passed to pip. (You probably passed some other options to pip install because without privileges, by default, pip install will just fail. Did you do sudo pip install perhaps? Did you do pip install as an admin user into a homebrewed Python?)
The right way to do this is to only ever install Twisted into virtual environments. You can create a virtual environment with the -p option to virtualenv, which tells it which Python to use for that environment. Then, with the correct virtual environment active, you can pip install twisted and everything should work as you expect.

I had the same import error problem, providing another possible solution here:
I have zope.interface 4.4.2 installed, it turned out that my twisted version is too old. By upgrade twisted solved my problem.
pip install --upgrade twisted

Thanks Glyph,
Finally I find following simple command could directly fix this problem, because Kivy use his own virtualenv environment, but I do appreciated your kindly help.
kivy -m pip install twisted
Best Wish to you,

zlib cannot be installed using yum

I am working on a RHEL system. I have two versions of Python installed on my system: Python 2.4 and Python 2.7, but I have created an alias in the .bashrc file so that the python command prompts Python 2.7 instead of Python 2.4.
I need to install zlib in my system. I tried to install it using the yum command:
yum install zlib
yum install zlib-devel
both worked fine, but when I type "python", I still cannot see zlib installed:
[root#mymachine]# python
Python 2.7 (r27:82500, Jan 18 2012, 17:03:29)
[GCC 4.1.2 20080704 (Red Hat 4.1.2-51)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import zlib
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ImportError: No module named zlib
But if I import zlib from Python 2.4, it works! Why? I need zlib to be installed using Python 2.7. How can I do that? Thank you in advance!

Generally you will only find RPMs for the default Python version in the yum repository, however that shouldn't really be applicable here since zlib should be installed by default in your Python 2.7 installation.
Check sys.path using import sys; print sys.path and make sure that you have the lib directories for your Python 2.7 installation, it is possible that whatever you are doing in .bashrc is causing you to pick up the Python 2.4 environment.
Here is the location of my zlib module, which may be useful in trying to track down the location of yours so you can make sure it is on sys.path.
>>> import zlib
>>> zlib
<module 'zlib' from '/usr/local/lib/python2.7/lib-dynload/zlib.so'>
If you cannot find it then you should reinstall Python 2.7.

The zlib and zlib-devel packages are the C shared and development libraries, respectively; the zlib you are importing in Python 2.4 is the one that shipped in the python-libs package:
$ rpm -qf /usr/lib64/python2.4/lib-dynload/zlibmodule.so
python-libs-2.4.3-46.el5
I don't know where you got your Python 2.7 from, but zlib is part of the standard library--it should have been built with Python. You will need to acquire a zlib module that was built against Python 2.7.

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.

how to install Matplotlib on Cygwin?

I'm trying to install Matplotlib 1.0.1 version on latest Cygwin. In the processing, there is a weird fork error cannot be solved. I googled similar questions and found that it might be solved by manually running gcc/g++ with matplotlib 0.98.5.2 : http://innuendopoly.org/arch/matplotlib-cygwin. But it doesn't work under 1.0.1 version. Does anybody encounter the same problem?

Here are instructions for how to install matplotlib 1.1.0 on Cygwin
http://berlinbrowndev.blogspot.com/2012/01/python-matplotlib-plotting-setup-for.html
Python matplotlib plotting setup for cygwin
Matplotlib is a popular python library for generating plot graphics. It works with cygwin win32 but some non-intuitive steps are required.
Install cygwin:
CYGWIN_NT-5.1 1.7.9(0.237/5/3) 2011-03-29 10:10 i686 Cygwin
I am using cygwin with setup 2.7.3
Install python through cygwin:
This document describes installing python and matplot with cygwin. For most windows users and cygwin users, normally you would use the external python executable. I tend to prefer all of my script oriented applications running through cygwin including python.
Python 2.6.5 (r265:79063, Jun 12 2010, 17:07:01)
[GCC 4.3.4 20090804 (release) 1] on cygwin
In the cygwin setup.exe installer, install:
The freetype libs, python-gtk, python-tk, libpng
gcc
Download matplotlib from sourceforge:
I am using the latest version matplotlib-1.1.0 as of 1/2012.
Download and extract the matplotlib tarball
Issues with standard python install and cygwin:
The typical 'python setup.py install' will not work with cygwin. You need to modify a configuration file and run some other additional commands.
In the root directory of the expanded matplotlib directory, copy the setup.cfg.template configuration file to setup.cfg. Edit setup.cfg.
Around line 70 in the file is a commented line, uncomment the line such that you have:
tkagg = False
Run install and watch it fail
Try running 'python setup.py install'
It should fail with an error like the following:
2 [main] python 2796 C:\cygwin\bin\python.exe: *** fatal error - unable to remap C:\cygwin\bin\cyggfortran-3.dll to same address as parent: 0x18660000 != 0x69780000
Stack trace:
Run the rebase command OUTSIDE OF THE TYPICAL CYGWIN ENV
Exit cygwin and close all cygwin instances including the one you are working with. You won't be using the typical cygwin prompt for the next command.
In windows explorer, open the cmd.exe or windows command
You will need to run rebaseall. First, shut down any long running processes like sshd, close all Cygwin prompts and so on.
Type the following commands:
cd \cygwin\bin
ash
PATH=. rebaseall -v
...
And you should get several lines of output.
Run install and watch it succeed
Try running 'python setup.py install' command again in the matplotlib directory
Running Example Program:
# python
Python 2.6.5 (r265:79063, Jun 12 2010, 17:07:01)
[GCC 4.3.4 20090804 (release) 1] on cygwin
Type "help", "copyright", "credits" or "license" for more information.
import matplotlib.pyplot as pyplot
pyplot.pie([1,2,3])
pyplot.show()
pyplot.savefig('f.png')
pyplot.savefig('x.eps')

These steps taken from www.scivision.co worked for me:
Run Cygwin setup: (For some reason the original command posted in the source link did not work for me)
install packages: (most of these you may already have)
pkg-config
ghostscript
libfreetype-devel
libpng-devel
libgtk2.0-devel
gcc-g++
git
openbox
python3-numpy
python3-pyqt5
python3-devel
Then from Cygwin Terminal:
easy_install-3.6 pip
pip install --upgrade six
pip install matplotlib
Then tested from python console:
import matplotlib
matplotlib.__version__

Installation worked for me as described by Felix above.
But to use matplotlib you need to start the Xserver from Cygwin first:
startxwin
and then start your script.