在尝试使用python连接到wifi网络时出现ConnectionError

Question

To connect to network from my Raspberry Pi, I'm using this python library . My problem is that I'm constantly getting ConnectionError, even through I'm handling it in try/except block, or at least I think I'm handling. This program scans air interface for wifi networks, then excludes ones without matching prefix, and then sorts matching ones by signal quality. After that, connectToGateway() is trying to connect to the best one and if it fails, it looks for second one in the list and so on. If scheme for some network was saved before, it reuses it (that's what AssertionError exception is handling). My code:

from wifi import Cell, Scheme
from collections import namedtuple
from operator import attrgetter
from wifi.exceptions import ConnectionError
from optparse import OptionParser


class NetworkConnection:
    def __init__(self, prefix, interface, password):
        self.prefix = prefix
        self.interface = interface
        self.password = password

    def discover_avalible_networks(self, interface=None):
        all_networks = []
        interface = self.interface
        avalible_networks = Cell.all(interface)
        for network in avalible_networks:
            all_networks.append(network)
        return all_networks

    def select_appropriate_networks(self, prefix=None):
        appropriate_network = namedtuple('network', 'ssid quality encrypted encryption_type')
        appropriate_networks = []
        prefix = self.prefix
        for network in self.discover_avalible_networks():
            if network.ssid.startswith(prefix):
                appropriate_networks.append(
                appropriate_network(network.ssid, network.quality, network.encrypted, network.encryption_type))
        return appropriate_networks

    def sort_appropriate_networks(self):
        unsorted_appropriate_networks = self.select_appropriate_networks()
        sorted_appropriate_networks = sorted(unsorted_appropriate_networks, key=attrgetter('quality'), reverse=True)
        return sorted_appropriate_networks

    def connect_to_gateway(self, interface=None, password=None):
        interface = self.interface
        password = self.password
        networks = self.sort_appropriate_networks()
        for network in networks:
            try:
                print("Trying to connect to {}").format(network.ssid)
                scheme = Scheme.for_cell(interface, network.ssid, network, password)
                scheme.save()
                scheme.activate()
                print("Connected to {}").format(network.ssid)
                break
            except AssertionError:
                scheme = Scheme.find(interface, network.ssid)
                scheme.activate()
                print("Connected to {}").format(network.ssid)
                break
            except ConnectionError:
                print("Couldn't connect to {}").format(network.ssid)
                scheme = Scheme.find(interface, network.ssid)
                scheme.delete()
                continue

if __name__ == "__main__":
    parser = OptionParser()
    parser.add_option('-p', '--prefix', dest='prefix', help="Specify gateway ssid prefix")
    parser.add_option('-i', '--interface', dest='interface', help="Specify name of wireless interface of choice")
    parser.add_option('-q', '--password', dest='password',
                      help="Specify password for the wireless network of choice")
    options, args = parser.parse_args()
    wireless_connection = NetworkConnection(prefix=options.prefix, interface=options.interface,
                                            password=options.password)
    wireless_connection.connect_to_gateway()

And results:

So it looks like it's not catching this error.

Answer 1

That ConnectionError isn't being caught because it's not being raised by the scheme.activate() call inside the try section, it's being raised by the scheme.activate() call on line 52, inside the except AssertionError section.

I assume that the wifi module docs tell you to catch AssertionError like that, but it's a bit weird. AssertionError is intended to be used to catch logic bugs in programs, IOW, things that should never happen if the program logic is correct, it's not supposed to be used to catch bad data or bad environment conditions. So normally, if a program raises AssertionError it's a sign that the program itself needs fixing.

I'm not familiar with that wifi module, so I don't know how to properly fix your problem. But the code seems to be having problems activating the Scheme returned by the Scheme.find call inside that except AssertionError section. I guess you could put that whole try.. except block inside a while loop with a small time delay at the end, and just keep looping until you get a working connection.