Homebrew will cause problems when building software from source if it is installed in /usr/local. This is the default, which is a bad choice as this path is in the default search path of compilers and other tools. Therefore builds from other packaging software might pick up the wrong dependency, using Homebrew's version instead of their own.
Years ago, in the very beginning of the project, even MacPorts was using /usr/local. But it turned out not to cooperate with other tools as is documented in their FAQ. Unfortunately Homebrew developers didn't want to hear about prior experiences and ignored such facts...
In general, it is usually better to stick to one tool only to avoid all problems. MacPorts is doing their best to patch out any harcoded paths, e.g. to /sw which is used by Fink. So usually it will work, but having anything installed in /usr/local will definitely cause problems for it.
I don't know pkgsrc enough to say if it is really affected the same way, but my best guess is that this problem applies to it as well.
There don't seem to be any open bugs for digikam or grass in MacPorts. You should report your problems to them directly with new tickets to get assistance.
Generally, homebrew will install a formula into /usr/local/Cellar/formula and then place a link at /usr/local/bin/formula.
To make use of your installed formulae, make sure /usr/local/bin is in your $PATH. Show your $PATH by typing
echo $PATH
If /usr/local/bin is not in your $PATH, put this line at the end of your ~/.profile file.
export PATH="/usr/local/bin:$PATH"
Now, check what pythons are found on your OSX by typing:
which -a python
There should be one python found at /usr/bin/ (the Apple python) and one at /usr/local/bin/ which is the Homebrew python.
which python
will show you, which python is found first in your $PATH
and will be executed when you invoke python.
If you want to know, where the executable is, show it by typing
ls -l $(which python)
This could look like this:
lrwxr-xr-x 1 root wheel 68 7 Mai 13:22 python -> /usr/local/bin/python
This will work for pip as well.
If you show the results of this steps, we can probably help you much easier.
-- UPDATE --
You have /usr/local/bin/python linked to /usr/local/Cellar/python/2.7.9/bin/python. -> brew install python worked.
show, if pip is installed by typing
brew list python | grep pip
You should see
/usr/local/Cellar/python/2.7.9/bin/pip
If not, check, if there are links, which are not done with brew install. Told you something like this:
"Error: The `brew link` step did not complete successfully
The formula built, but is not symlinked into /usr/local"
To force the link and overwrite all conflicting files:
brew link --overwrite python
To list all files that would be deleted:
brew link --overwrite --dry-run python
** NO standard Apple /usr/bin/python **
link from /usr/local/Cellar/python/2.7.9/bin/python to /usr/bin/python
ln -s /usr/local/Cellar/python/2.7.9/bin/python /usr/bin/python
This is necessary for all python scripts beginning with #!/usr/bin/python. Especialy easy_install will fail, if link is not there.
Now, you are able to run
easy_install pip
Hope, you're making progress
Best Answer
You can tell Homebrew to use its own directory, and then add that to the path. Although not for the same purpose, this excerpt from the installation guide tells it:
Source: https://github.com/mxcl/homebrew/wiki/installation