def add(folder, index=1):
"""
Adds the given folder to the python path. Supports namespaced packages.
By default, packages in the given folder take precedence over site-packages
and any previous path manipulations.
Args:
folder: Path to the folder containing packages, relative to ``os.getcwd()``
position: Where in ``sys.path`` to insert the vendor packages. By default
this is set to 1. It is inadvisable to set it to 0 as it will override
any modules in the current working directory.
"""
# Check if the path contains a virtualenv.
site_dir = os.path.join(folder, 'lib', 'python' + sys.version[:3], 'site-packages')
if os.path.exists(site_dir):
folder = site_dir
# Otherwise it's just a normal path, make it absolute.
else:
folder = os.path.join(os.path.dirname(__file__), folder)
# Use site.addsitedir() because it appropriately reads .pth
# files for namespaced packages. Unfortunately, there's not an
# option to choose where addsitedir() puts its paths in sys.path
# so we have to do a little bit of magic to make it play along.
# We're going to grab the current sys.path and split it up into
# the first entry and then the rest. Essentially turning
# ['.', '/site-packages/x', 'site-packages/y']
# into
# ['.'] and ['/site-packages/x', 'site-packages/y']
# The reason for this is we want '.' to remain at the top of the
# list but we want our vendor files to override everything else.
sys.path, remainder = sys.path[:1], sys.path[1:]
# Now we call addsitedir which will append our vendor directories
# to sys.path (which was truncated by the last step.)
site.addsitedir(folder)
# Finally, we'll add the paths we removed back.
# The final product is something like this:
# ['.', '/vendor-folder', /site-packages/x', 'site-packages/y']
sys.path.extend(remainder)
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