"""
A decorator that allows requiring imports/functions

E.g. from hg.py of silvermirror:

@requires("mercurial.ui")
def update(host, path):
  _ui = ui.ui()
  ....

@requires("lxml")
def repositories(url):
  element = lxml.html.parse(url)
  ...

@requires("repositories")
def foo(bar):
    "something that uses the repositories function above"

@requires("repositories", "update")
def main(args=sys.argv[1:]):
  ...
"""

# Tags: {dependencies}