serial/__init__.py

#!/usr/bin/env python
#
# This is a wrapper module for different platform implementations
#
# This file is part of pySerial. https://github.com/pyserial/pyserial
# (C) 2001-2016 Chris Liechti <cliechti@gmx.net>
#
# SPDX-License-Identifier:    BSD-3-Clause

import importlib
import sys

from serial.serialutil import *
#~ SerialBase, SerialException, to_bytes, iterbytes

VERSION = '3.1a0'

# pylint: disable=wrong-import-position
if sys.platform == 'cli':
    from serial.serialcli import Serial
else:
    import os
    # chose an implementation, depending on os
    if os.name == 'nt':  # sys.platform == 'win32':
        from serial.serialwin32 import Serial
    elif os.name == 'posix':
        from serial.serialposix import Serial, PosixPollSerial, VTIMESerial  # noqa
    elif os.name == 'java':
        from serial.serialjava import Serial
    else:
        raise ImportError("Sorry: no implementation for your platform ('%s') available" % (os.name,))


protocol_handler_packages = [
    'serial.urlhandler',
]


def serial_for_url(url, *args, **kwargs):
    """\
    Get an instance of the Serial class, depending on port/url. The port is not
    opened when the keyword parameter 'do_not_open' is true, by default it
    is. All other parameters are directly passed to the __init__ method when
    the port is instantiated.

    The list of package names that is searched for protocol handlers is kept in
    ``protocol_handler_packages``.

    e.g. we want to support a URL ``foobar://``. A module
    ``my_handlers.protocol_foobar`` is provided by the user. Then
    ``protocol_handler_packages.append("my_handlers")`` would extend the search
    path so that ``serial_for_url("foobar://"))`` would work.
    """
    # check and remove extra parameter to not confuse the Serial class
    do_open = not kwargs.pop('do_not_open', False)
    # the default is to use the native implementation
    klass = Serial
    try:
        url_lowercase = url.lower()
    except AttributeError:
        # it's not a string, use default
        pass
    else:
        # if it is an URL, try to import the handler module from the list of possible packages
        if '://' in url_lowercase:
            protocol = url_lowercase.split('://', 1)[0]
            module_name = '.protocol_%s' % (protocol,)
            for package_name in protocol_handler_packages:
                try:
                    importlib.import_module(package_name)
                    handler_module = importlib.import_module(module_name, package_name)
                except ImportError:
                    continue
                else:
                    if hasattr(handler_module, 'serial_class_for_url'):
                        url, klass = handler_module.serial_class_for_url(url)
                    else:
                        klass = handler_module.Serial
                    break
            else:
                raise ValueError('invalid URL, protocol %r not known' % (protocol,))
    # instantiate and open when desired
    instance = klass(None, *args, **kwargs)
    instance.port = url
    if do_open:
        instance.open()
    return instance