and

pkg_resources

is used to "activate" from a list of wheels?

pkg_resources.___init___.py

contains a global variable

working_set

that is a default

WorkingSet

object. When constructing a default

WorkingSet

object, i.e.: passing in no search path, it uses

sys.path

and it scans that whole path for distributions. This gets done before Pex gets a chance to scrub sys.path. As such the time to scan depends on how many packages are installed on sys.path n your machine.