Recently I've installed Python 3 after using 2 for quite a while, so I have many libraries for Python that I've installed using pip. I've already started using the symlink python3, but what else do I need to do to change over?
For example, while I have made the alias python=python3, I don't know about the modules I've installed with pip. I was using a version of pip for Python 2, but does that mean modules were written for Python 2 and not 3? Do I now need to start using pip3 (or make a corresponding alias pip=pip3 or pip=pip3.5)? If modules were installed using the command pip, does that mean I have to reinstall them for Python 3 using pip3? If I do need to reinstall them for 3, should I start removing them from my Python 2 env as cleanup?
And another question that seems like it may entail a lot of work: How should I change all my virtual environments for Python projects? They were all Python 2 envs, and now I'm not sure whether it's necessary, useful, or possible to reinstall or upgrade the modules within them to the corresponding ones for Python 3.
Sorry if this seems like a duplicate question - I've searched and only found resources regarding "how to upgrade" rather than "what to do after upgrading". Thanks for your help!
It is strongly recommended not to symlink python to Python 3, at least on Debian-based Linux distros. Debian utility scripts use both Python 3 and 2.7 to work (which means you already had a copy of Python 3 somewhere...), and as a consequence Debian-based distributions ship both versions. Symlinking can cause unexpected breakages. This may or may not be true on other systems, however, but with such ambiguity it is probably useful not to try.
Instead, live with symlinking python3 to Python 3. Leave python alone.
pip is usually symlinked to the corresponding pip program for 2.7. Use pip3 to specify you want to use the pip program for Python 3. If you use pip, you'll find modules for Python 3 being installed to Python 2.7 site directories and nothing will work as you expect it to. There should be no reason why you can't symlink pip to pip3, but I'd still not recommend it - it's better to tread cautiously in this regard.
You don't need to change your current virtual environments. Just create new ones with virtualenv, pointing to the correct Python program to use. This is the whole point of virtual environments: to sandbox different Python versions, so that neither of them adversely interact with each other.
If you have projects you really want to ship to Python 3, I'd recommend using a version control system to back up your current files, and then reproducing them in a new virtual environment configured for Python 3. This is quick, simple and painless.
Related
Background
Currently, I have Python 2.7.17 and Python 3.8.1 installed on my Mac (v 10.14.6). Both Python versions were downloaded directly from Python.org using a "macOS 64-bit installer" .pkg file, in late 2019. Both were installed here:
python2: /Library/Frameworks/Python.framework/Versions/2.7/bin/python2
python3: /Library/Frameworks/Python.framework/Versions/3.8/bin/python3
Currently, I use only pip (either pip2 or pip3, depending) to install python packages, which are saved here:
python2: /Library/Frameworks/Python.framework/Versions/X.X/lib/python2.7/site-packages
python3: /Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/site-packages
I am about to begin an online course which requires that I install miniconda in order to install the packages that I need for the course. But after having a very bad experience having Anaconda installed on my machine years ago, and it taking me months to remove it and re-create a clean Python install, I am nervous. I don't want my machine to become a mess again, rife with error messages that it can't find this or that python version or this or that python library.
Question(s)
Assuming there will now be multiple installations of Python on my machine (in addition to the versions that I already have, since I believe yet another version of python is installed along with conda), and there will be new places where python packages will be saved, what can I expect to change about how I write python after I install miniconda?
Is there anything I will need to do differently from what I am doing now when I write python code?
How can I ensure that everything remains working and compatible and I avoid the fate I suffered many years ago?
Happy to edit/clarify this question per user suggestions. Thanks!
Use conda environments and install Python into those environments. This ignores, by design, the versions of Python that are installed at the system level. Also, what's installed into environments (other than the one you're in) is ignored. As somebody who uses conda for all Python development, I don't even know what I have installed in /usr/local/bin/ or other places. Everything is in /path/to/miniconda3/envs/env_name_n. You don't have to uninstall other versions of Python you have elsewhere; the point of environments is to keep everything isolated.
What can I expect to change about how I write python after I install miniconda?
Is there anything I will need to do differently from what I am doing now when I write python code?
Use conda environments and use conda as your package manager. For almost every major project, it nearly a drop-in replacement for pip. Outside of managing dependencies, not much changes.
It seems I have several Python versions installed on my Mac (High Sierra). Do I really need more than one each of Python 2.7 and the most recent Python3?
I am primarily concerned about confusion when adding modules to the environments.
Here are the python executables I can find, excluding symlinks. Do I need them all? Does Apple need one version just for the OS? (Maybe that's Ruby I'm thinking of._)
/usr/bin/python
/usr/local/Cellar/python/2.7.13/Frameworks/Python.framework/Versions/2.7/bin/python
/usr/local/Cellar/python/2.7.13/bin/python
/usr/local/Cellar/python/2.7.13/share/python
/usr/local/Cellar/python/3.7.1/libexec/bin/python
On MacOS, you need to have the system-installed Python 2 in /usr/bin/python because some system functionality depends on it.
If you have other versions installed via Homebrew or etc, that's strictly optional. For developing code in Python, definitely install a recent version of Python 3; you should not be developing new code in the legacy version 2. It will run out of support in a year or so, and many important third-party libraries etc have already abandoned support for it.
If you do need to maintain Python 2 code, having a Homebrew version of the most recent Python 2.7.13 is probably a good idea. The system /usr/bin/python is at version 2.7.10 as of MacOS Mojave; and if we extrapolate from Apple's update policy history for third-party open-source software in the system, it will probably remain there for many years.
Homebrew is just one of many ways to install additional Python versions, but since this is what you seem to be using already (as indicated by the /usr/local/Cellar paths) I will not go into alternatives.
For switching between versions, virtualenv is the common baseline, though there are many add-ons like pyenv etc which add convenience features or alternative models for switching between projects which require different versions of Python and various packages.
Note: this answer might be primarily based opinioned.
First, in macos, I encourage you to use brew to install python. So, if you want to instal Python 3 run:
$ brew install python
Probably it is already installed, so to update it run:
$ brew upgrade python
This will upgrade to the latest version of Python 3. In general, if you start a new project you should use Python 3. Remember that Python 2 will be deprecated at the end of this year 2019.
Second, I highly recommend you to use virtual environments to avoid having issues with dependencies. You can create a virtual environment running:
$ python3 -m venv .ven
This will create a virtual environment in .venv in your current working directory.
As an alternative you can use pipenv to track dependencies too which I also encourage you to install using brew.
$ brew install pipenv
Then you create a virtual environment running:
$ pipenv --three
Keep in mind that you will have two versions of Python in your machine python which is Python 2 (installed by default in your machine) and python3 which is Python 3. Then, if you want to run Python 2 just type python, while if you want to run Python 3 type python3.
Finally, you can also keep track of several python versions using pyenv. This is very useful if you need to use multiple versions of Python for example Python 3.1, 3.2, 3.3..., 3.6, 3.7.1, 3.7.2, 3.7.3, etc.
This is what has been useful in my experience using macOS. You could also use Docker to completely isolate your environment, but probably the first two points is enough if you are a beginner.
While Python 3.x is what python solutions should be implemented in today, many existing python applications, modules, etc, are implemented and maintained in 2.7 or lower. Sometimes you'll find multiple versions of python on your computer because applications you've downloaded in the past had you install them so their application would work properly on your machine. As long as you don't want, or need applications that may depend on past versions of python, you can update to the latest one and delete the old versions.
If you are planning on developing in python, and you can use the latest version, you should definitely do so. If you rid of the versions of python on your machine, applications, modules/scripts, etc may not work or function properly.
Python comes pre-installed on Mac OS X, but it is not required to be on your machine for your computer to function, just the applications that may be on your machine that may use Python.
Using Ubuntu 16.04.
I was doing development in Python2.7, although recently moved to Python3.5, both of which come by default. The problem is, I find all the python libraries have to be reinstalled or downloaded for the next Python3. Also, the behaviour of Python seems weird because to execute the same script in python3, I have to enter in terminal
python3 script.py
which is different from other applications where I do not have to give the version number. Anyway, the questions I am trying to find answers are
To what extent are the libraries, packages (such as pip etc.) shared between 2.7 and 3.5? Or do I need double installations (and double the space) for everything now? A bit space limited in my old laptop.
Most of the installation instructions and commands I find online do not specify whether they are for 2 or 3. Given that I have two versions, how do I control/make sure they go to 3.5?
Is it advisable and possible to completely remove everything related to 2.7? Can I keep working with 3.5?
The first thing you need to know is that all official libraries and python tools for python3 got the "3" character to separate them from the previous versions. So, you need to use pip3, and not pip, python3, not python, and the packages are called python-pygame, not python-pygame.
So, to answer to you in order:
Yes, the you have to double the space needed if you decide to use both python2 and python3
Usually, if in the tool name there is 3, it is for python3, and if not it's for python2
Python2 and python3 are completly indipendent (different path, indipendent versions, etc.) so having python 2.7 installed doesn't affect python3 BUT since python 3 is the next version of python 2, it makes it obsolete (in my opinion) so if you don't have enough space for both, keeping python2 is absolutely not needed nor useful
If you want to control your python execution then you have various method or techniques:
For downloading packages according to version
You can use pip{version-name} to download the libraries. Like if you want to download library of python 2.7 then write
pip2.7 install package-name
for python 3.5 then use
pip3.5 install package-name
For execution of program:
If you want to execute the program accoridng to you choice of version then just use
python{version-name} script.py
eg:
python2 script.py
python3 script.py
or you just write down the path of your python version on the top of script. Please refer this for more details:
Why do people write #!/usr/bin/env python on the first line of a Python script?
I want to move to python 3.0 and therefore remove the default python 2.7 (2.6,2.5...) installation on my mac. Including all the installed packages, $PATH,...
Does the python installer from python.org oder MacPorts installer provide an uninstaller, or is there a way to do this manually?
That's a COMPLETELY TERRIBLE idea, and you should never do that. You're likely to break dependencies and requirements for various software that expect to find the default Python in the default location.
Install your choice of Python 3 ( MacPorts, Python.org, whatever ). Update your local $PATH variables to use that Python / PythonPath.
If you don't trust my opinion, here's what official Python.org docs say:
http://docs.python.org/2/using/mac.html
The Apple-provided build of Python is installed in /System/Library/Frameworks/Python.framework and /usr/bin/python, respectively. You should never modify or delete these, as they are Apple-controlled and are used by Apple- or third-party software. Remember that if you choose to install a newer Python version from python.org, you will have two different but functional Python installations on your computer, so it will be important that your paths and usages are consistent with what you want to do.
I new to Python and to programming in general. I'm a novice, and do not work in programming, just trying to teach myself how to program as a hobby. Prior to Python, I worked with Ruby for a bit and I learned that one of the biggest challenges was actually properly setting up my computer.
Background: I'm on a Macbook with OSX 10.7.
With Ruby, you have to (or rather, you should), edit your ./profile and add PATH info. When you install and use RVM, there are additional items you need to add to your bash_profile.
Do you have to make similar changes with Python? What are the best practices as I'm installing/getting started to ensure I can install modules and packages correctly?
python works out of the box on OS X (as does ruby, for that matter). The only changes I would recommend for a beginner are:
1) Python likes to be reassured that the terminal can handle UTF-8 before it will print Unicode strings. Add export LANG=en_US.UTF-8 to .profile. (It may be that the .UTF-8 part is already present by default on Lion - I haven't checked since Snow Leopard.) Of course, this is something that will help you in debugging, but you shouldn't rely on it being set this way on other machines.
2) Install pip by doing easy_install pip (add sudo if necessary). After that, install Python packages using pip install; this way, you can easily remove them using pip uninstall.
Take a loot at Python on the Macintosh page first. Like it says, Python comes pre-installed on Mac OS X. It means that you don't have to do anything special in order to use it.
To get started, you can run a Terminal.app, type python and that will get you Python interactive shell up and running.
However, Python on OS X might be of a slightly older version. For example, OS X 10.7.3 comes with Python 2.7.1, whereas latest release version of the Python is 3.2.3. If you want to use other versions, then you will have to install them. Then it all depends on what, where and how you install. If you want to have multiple versions alongside, you may need to set some environment variables like PATH to have binaries you installed found by the bash etc. You can do it through bash ~/.profile if needed.
But until you get to that point - don't worry about it use a version shipped with OS X. Once you want a newer one - download and install it. Then, if it doesn't work out of the box or you have any other problems or concerns, feel free to ask a more specific question.