What steps will reproduce the problem?

1. Follow installation instructions on http://cantera.github.io/docs/sphinx/html/install.html without prior exposure to cantera and a fresh install of homebrew (e.g. students in a combustion class)

What is the expected output? What do you see instead?

• Expected behavior would be flawless installation. Instead, neither installation for python 2.7 nor python 3.4 works 'out of the box'.

What version of the product are you using? On what operating system?

• Cantera 2.1.2 on OSX (Yosemite)

Please provide any additional information below.

• for python 2.7 instructions, there is a critical line missing: "easy_install pip" before pip is usable

• an attempt to use python3 instead fails at the installation of cantera, where it is not clear what flags need to be provided to force usage of python3. If one attempts to just run "brew install cantera", the following error appears:

$ brew install cantera

==> Installing cantera from homebrew/homebrew-science

cantera: Unsatisfied dependency: cython

Homebrew does not provide Python dependencies; install with:

pip install cython

Error: An unsatisfied requirement failed this build.

As an aside for windows installation: there is a stumbling block in the numpy installation, where executables are no longer provided. Instead, it requires installation of "wheels". It would be helpful if instructions for Cantera would include the following after downloading the .whl file:

cd C:\Python34\Scripts pip install "C:\Users\<yourname>\Downloads\numpy-<appropriate_version>.whl"

"easy_install pip" should not be necessary, as the version of Python installed by Homebrew comes with pip. Running 'easy_install pip' will install pip for the system Python, which is not what these build instructions are for.

I realize that there is a formatting error in the instructions -- the step after installing Homebrew should be to run the following three commands:

  brew tap homebrew/science
  brew update
  brew install python scons sundials

But these are not displayed with the correct formatting. Did you run these commands? Does running these before trying to install Cantera fix the problems?

What error do you get trying to install the Cantera for Python 3? It should install automatically if you have the necessary prerequisites installed (python3 and the python3 versions of Numpy and Cython).

Comment deleted

I was able to install everything correctly, but this required the stated 'easy_install pip'. Cantera did load from the python prompt when I stated 'import cantera' so I assume I was successful. I did change the path as indicated so I believe I'm using homebrew's python, not the native one. Apart from that, the cantera installation with python3 fails entirely. Note: I usually don't use OSX, but was trouble-shooting for my students.

I tested this again on a Mac with a clean copy of OS X 10.10.2 and found that the following steps were sufficient to install Cantera for both Python 2 and Python 3:

<install XCode from the app store>
sudo xcode-select --install
sudo xcodebuild -license
<install homebrew>
brew tap homebrew/science
brew update
brew install python scons sundials
pip install cython numpy
brew install python3
pip3 install numpy cython
brew install -v cantera

The only step not in the directions already is the extra step for the XCode EULA that Apple added at some point (and which the Homebrew installer will direct you to do anyway).

The Homebrew installer for Python specifically mentions that it installs pip, so installing it with easy_install should not be required.

I did not find modifications to the path necessary, as apparently between 10.9 and 10.10 Apple changed the default path order to list /usr/local/bin ahead of /usr/bin. You can confirm this by looking at the file /etc/paths. If your $PATH does not have the directories in /etc/paths in that order, then you may need to check your user-specific configuration files to see if they are modifying $PATH.

If you still find this set of steps to be inadequate, I would appreciate seeing the output from running all of these (up to the failure) on a clean OS X machine.

Ray,

Thanks for looking into this. I was able to get a clean copy of OS X 10.10.2 myself, and can verify that the updated instructions are mostly ok. The only issue I ran into was right before the last step (cantera), when I had to 'brew link --overwrite scons'.

Retracing my previous installation steps, I believe that it wasn't sufficiently clear to me that cantera on OSX requires python 2, even if you're just intending to use python 3 (this explains the original error I reported, as I had skipped the python 2 packages). This is different from the windows version (that I had just tested before), where you need to choose which one. Linux is a different matter, but I guess it has the same dependencies as OSX (for legacy reasons, I'm still mostly on python 2 there, so I never realized this dependency).

I'd still ask you to update the current instructions, as I can report that a 'field test' of having students just follow the online steps failed (and not being used to homebrew, it even threw me for a loop despite having installed cantera dozens of times on linux over the past ten years). As a personal opinion, I'd recommend omitting all flags (including -v) from a default 'brew install cantera' and explain options separately. There will always be people that are new to command line tools and keeping it simple is a plus.

Finally, as pointed out in my initial report, even the windows installation changed: there is no longer an 'installer' (executable) for numpy. So the instructions should be updated here as well. Now, it requires installation of "wheels". It would be helpful if instructions for Cantera windows installation would include the following after downloading the .whl file:

cd C:\Python34\Scripts pip install "C:\Users\\Downloads\numpy-.whl"

As always, thanks for all the work you're putting into maintaining cantera.

The need to run 'brew link --overwrite scons' suggests that a copy of SCons had already been installed in /usr/local, so perhaps that was not a totally clean installation. I think users will have to consult the Homebrew documentation if any issues arise in installing the prerequisites.

The difference with OS X and Windows is that on OS X you are compiling Cantera from source, so you need all the build dependencies, which include Python 2, Scons, and Cython. I don't think there's anything in the instructions that suggests that any of these are optional, but further clarifying this in the instructions wouldn't hurt.

I included '-v' in the list above just because if there was an error in Cantera installation, the verbose logs would be helpful in diagnosing the cause. Are there any other options which are not adequately described in the instructions?

Thank you for pointing out the change in how the pre-compiled Windows packages are being distributed from Christoph Gohlke's repository. I haven't had to reinstall Python on a Windows system recently, so I was unaware of this packaging change, and an update to the instructions is certainly warranted.

Ray,

... the OSX was a 'fresh' update from 10.9, so it could be that scons had persisted from there. However, I am positive that homebrew hadn't touched the system before.

The difference between windows installer and OSX makes sense, but it's not entirely obvious why the cantera compilation toolchain requires both versions of python (other than perhaps for historic reasons).

Please take this feedback with a grain of salt: I usually can work around these issues, but facing a class with 15+ students, most of which had trouble installing cantera, points out that instructions aren't clear in their current form.

Homebrew may not have touched the system before, but SCons could have been manually installed in /usr/local (i.e. from previously attempting to build Cantera).

Python 2 is required because SCons uses Python 2 and has not yet been updated to work with Python 3. When SCons is eventually updated to work with Python 3, it should be possible to update the Cantera build scripts to work with either.

Suggestions for improvements to the installation instructions are always welcome.

Thanks for your explanations: I wasn't aware of scons not supporting python 3 yet. Based on my observations, most students were ok with the Windows installation after I provided instructions on how to deal with the .whl files. Everyone got stumped with the OSX installation, hence my report.

Here is a draft of some updates to the instructions for installing on OS X and Windows:

https://github.com/Cantera/cantera/blob/doc-work/doc/sphinx/install.rst

Please let me know if these address the issues or whether there are any modifications you would suggest.

Thank you, it is definitely improved. To further enhance, I'd suggest to add some explanations and number installation steps. I am attaching what I just posted for my class.

This issue was closed by revision r3414.