capybara/virtualenv/lib/python2.7/site.py
def addsitedir(sitedir, known_paths=None):
    """Add 'sitedir' argument to sys.path if missing and handle .pth files in
    'sitedir'"""
    if known_paths is None:
        known_paths = _init_pathinfo()
        reset = 1
    else:
        reset = 0
    sitedir, sitedircase = makepath(sitedir)
    if not sitedircase in known_paths:
        sys.path.append(sitedir)        # Add path component
    try:
        names = os.listdir(sitedir)
    except os.error:
        return
    names.sort()
    for name in names:
        if name.endswith(os.extsep + "pth"):
            addpackage(sitedir, name, known_paths)
    if reset:
        known_paths = None
    return known_paths
def addsitedir(sitedir, known_paths=None):
    """Add 'sitedir' argument to sys.path if missing and handle .pth files in
    'sitedir'"""
    if known_paths is None:
        known_paths = _init_pathinfo()
        reset = 1
    else:
        reset = 0
    sitedir, sitedircase = makepath(sitedir)
    if not sitedircase in known_paths:
        sys.path.append(sitedir)        # Add path component
    try:
        names = os.listdir(sitedir)
    except os.error:
        return
    names.sort()
    for name in names:
        if name.endswith(os.extsep + "pth"):
            addpackage(sitedir, name, known_paths)
    if reset:
        known_paths = None
    return known_paths
Add 'sitedir' argument to sys.path if missing and handle .pth files in
    'sitedir