replace threw with raised (#16714)

diff --cc Lib/pkgutil.py
index 2c8a31b41d61e7f88f9f2776ae5f9b067b212365,51da0b1bb52641d818852f4e3d6c45c822ed08b5..a5de04d257484d6cb948adc943a1e9a56f79ec07
--- 1/Lib/pkgutil.py
--- 2/Lib/pkgutil.py
+++ b/Lib/pkgutil.py
@@@ -485,29 -463,17 +485,29 @@@ def get_loader(module_or_name)
  def find_loader(fullname):
      """Find a PEP 302 "loader" object for fullname
  
 -    If fullname contains dots, path must be the containing package's __path__.
 -    Returns None if the module cannot be found or imported. This function uses
 -    iter_importers(), and is thus subject to the same limitations regarding
 -    platform-specific special import locations such as the Windows registry.
 +    This is s convenience wrapper around :func:`importlib.find_loader` that
 +    sets the *path* argument correctly when searching for submodules, and
 +    also ensures parent packages (if any) are imported before searching for
 +    submodules.
      """
 -    for importer in iter_importers(fullname):
 -        loader = importer.find_module(fullname)
 -        if loader is not None:
 -            return loader
 -
 -    return None
 +    if fullname.startswith('.'):
 +        msg = "Relative module name {!r} not supported".format(fullname)
 +        raise ImportError(msg)
 +    path = None
 +    pkg_name = fullname.rpartition(".")[0]
 +    if pkg_name:
 +        pkg = importlib.import_module(pkg_name)
 +        path = getattr(pkg, "__path__", None)
 +        if path is None:
 +            return None
 +    try:
 +        return importlib.find_loader(fullname, path)
 +    except (ImportError, AttributeError, TypeError, ValueError) as ex:
 +        # This hack fixes an impedance mismatch between pkgutil and
 +        # importlib, where the latter raises other errors for cases where
-         # pkgutil previously threw ImportError
++        # pkgutil previously raised ImportError
 +        msg = "Error while finding loader for {!r} ({}: {})"
 +        raise ImportError(msg.format(fullname, type(ex), ex)) from ex
  
  
  def extend_path(path, name):

diff --cc Lib/test/test_urllib2.py
Simple merge