Question or problem about Python programming:
I recently installed Python 2.7.3 on a CentOS machine by compiling from source. Python 2.7.3 is installed at /opt/python2.7 and when I installed it I just changed /usr/bin/python to point to the new version. This apparently is wrong though because when I did it it broke yum. I would get the following.
There was a problem importing one of the Python modules required to run yum. The error leading to this problem was: No module named yum Please install a package which provides this module, or verify that the module is installed correctly. It's possible that the above module doesn't match the current version of Python, which is: 2.7.3 (default, May 15 2012, 17:45:42) [GCC 4.4.4 20100726 (Red Hat 4.4.4-13)] If you cannot solve this problem yourself, please go to the yum faq at: http://yum.baseurl.org/wiki/Faq
I changed /usr/bin/python to point back to the python 2.6.6 but now 2.6.6 is the default version of python. Any idea how to fix this?
How to solve the problem:
I have written a quick guide on how to install the latest versions of Python 2 and Python 3 on CentOS 6 and CentOS 7. It currently covers Python 2.7.13 and Python 3.6.0:
# Start by making sure your system is up-to-date: yum update # Compilers and related tools: yum groupinstall -y "development tools" # Libraries needed during compilation to enable all features of Python: yum install -y zlib-devel bzip2-devel openssl-devel ncurses-devel sqlite-devel readline-devel tk-devel gdbm-devel db4-devel libpcap-devel xz-devel expat-devel # If you are on a clean "minimal" install of CentOS you also need the wget tool: yum install -y wget
The next steps depend on the version of Python you’re installing.
For Python 2.7.14:
wget http://python.org/ftp/python/2.7.14/Python-2.7.14.tar.xz tar xf Python-2.7.14.tar.xz cd Python-2.7.14 ./configure --prefix=/usr/local --enable-unicode=ucs4 --enable-shared LDFLAGS="-Wl,-rpath /usr/local/lib" make && make altinstall # Strip the Python 2.7 binary: strip /usr/local/lib/libpython2.7.so.1.0
For Python 3.6.3:
wget http://python.org/ftp/python/3.6.3/Python-3.6.3.tar.xz tar xf Python-3.6.3.tar.xz cd Python-3.6.3 ./configure --prefix=/usr/local --enable-shared LDFLAGS="-Wl,-rpath /usr/local/lib" make && make altinstall # Strip the Python 3.6 binary: strip /usr/local/lib/libpython3.6m.so.1.0
To install Pip:
# First get the script: wget https://bootstrap.pypa.io/get-pip.py # Then execute it using Python 2.7 and/or Python 3.6: python2.7 get-pip.py python3.6 get-pip.py # With pip installed you can now do things like this: pip2.7 install [packagename] pip2.7 install --upgrade [packagename] pip2.7 uninstall [packagename]
You are not supposed to change the system version of Python because it will break the system (as you found out). Installing other versions works fine as long as you leave the original system version alone. This can be accomplished by using a custom prefix (for example
/usr/local) when running configure, and using
make altinstall (instead of the normal
make install) when installing your build of Python.
Having multiple versions of Python available is usually not a big problem as long as you remember to type the full name including the version number (for example “python2.7” or “pip2.7”). If you do all your Python work from a virtualenv the versioning is handled for you, so make sure you install and use virtualenv!
vim `which yum` modify #/usr/bin/python to #/usr/bin/python2.4
/opt/python2.7/bin in your
PATH environment variable in front of
/usr/bin…or just get used to typing
pythonz, an active fork of pythonbrew, makes this a breeze. You can install a version with:
# pythonz install 2.7.3
Then set up a symlink with:
# ln -s /usr/local/pythonz/pythons/CPython-2.7.3/bin/python2.7 /usr/local/bin/python2.7 # python2.7 --version Python 2.7.3
ln -s /usr/local/bin/python2.7 /usr/bin/python
Alright so for me, the error being fixed is when there are different versions of python installed and yum can’t find a certain .so file and throws an exception.
yum wants 2.7.5 according to the error.
which python gives me /usr/bin/python python --version gives me 2.7.5
The fix for me was append /lib64 to the LD_LIBRARY_PATH environment variable.
The relevant content is /lib64/python2.7 and /lib64/python3.6.
Fixed the yum error for me with multiple python versions installed.
Daniel’s answer is probably the most ideal one as it doesn’t involve changing OS files. However, I found myself in a situation where I needed a 3rd party program which invoked python by calling
usr/bin/python, but required Python 2.7.16, while the default Python was 2.7.5. That meant I had to make
usr/bin/python point to a Python version of 2.7.16 version, which meant that
yum wouldn’t work.
What I ended up doing is editing the file
/usr/bin/yum and replacing the shebang there to use to the system default Python (in my case, that meant changing
#! /usr/bin/python to
#! /usr/bin/python2). However, after that running
yum gave me an error:
ImportError: No module named urlgrabber.grabber
I solved that by replacing the shebang in
/usr/libexec/urlgrabber-ext-down the same way as in
#! /usr/bin/python to
#! /usr/bin/python2. After that
This is a hack and should be used with care. As mentioned in other comments, modifying OS files should be last resort only.
I recommend, instead, updating the path in the associated script(s)
(such as /usr/bin/yum) to point at your previous Python as the interpreter.
Ideally, you want to upgrade yum and its associated scripts so that they
are supported by the default Python installed.
If that is not possible, the above is entirely workable and tested.
to whatever the path is of your old version until you can make the
above yum improvement.
Cases where you couldn’t do the above are if you have an isolated machine,
don’t have the time to upgrade rpm manually or can’t connect temporarily
or permanently to a standard yum repository.
If you want to try out rpm packages, you can install
binary packages based on the newest Fedora rpms, but recompiled
for RHEL6/CentOS6/ScientificLinux-6 on:
Florian La Roche
I read a piece with a comment that states the following commands can be run now. I have not tested myself so be careful.
$ yum install -y epel-release $ yum install -y python36