Currently shutil.copyfile only raises SpecialFileError for named pipes. When trying to use the function to copy a socket file, the exception raised depends on the platform, for example:

macOS: "[Errno 102] Operation not supported on socket: '/Users/guido/src/mypy/dmypy.sock'"
HP-UX: "[Errno 223] Operation not supported: 'example/foo'"
Solaris: "[Errno 122] Operation not supported on transport endpoint: 'example/foo'"
AIX: "[Errno 64] Operation not supported on socket: '../../example/foo'"
Linux: "[Errno 6] No such device or address: 'example/foo'"

This can be reproduced like:

    import os
    import shutil
    import socket
    import tempfile

    d = tempfile.mkdtemp()
    src = os.path.join(d, "src")
    dest = os.path.join(d, "dest")
    sock = socket.socket(socket.AF_UNIX)
    sock.bind(src)

    shutil.copyfile(src, dest)

Making shutil.copyfile raise SpecialFileError for socket files would improve the interface of this function since the same class of error could be ignored. This is mostly useful with shutil.copytree, which defaults to copyfile for its copy function.

See also: the comment from https://github.com/python/cpython/blob/e1b900247227dad49d8231f1d028872412230ab4/Lib/shutil.py#L245:

> # XXX What about other special files? (sockets, devices...)

This issue is being filed after coming up in pip's tracker here (in a comment by Guido): https://github.com/pypa/pip/issues/5306#issuecomment-383355379