Manage two or more printers of the same model

brother_ql/backends/helpers.py

@@ -67,10 +67,10 @@ def send(instructions, printer_identifier=None, backend_identifier=None, blockin
         """ No need to wait for completion. The network backend doesn't support readback. """
         return status
 
-    while time.time() - start < 10:
+    while time.time() - start < 60:
         data = printer.read()
         if not data:
-            time.sleep(0.005)
+            time.sleep(0.05)
             continue
         try:
             result = interpret_response(data)

brother_ql/backends/pyusb.py

@@ -47,11 +47,21 @@ def __call__(self, device):
 
     def identifier(dev):
         try:
-            serial = usb.util.get_string(dev, 256, dev.iSerialNumber)
-            return 'usb://0x{:04x}:0x{:04x}_{}'.format(dev.idVendor, dev.idProduct, serial)
+            # Based on this information (https://github.com/pyusb/pyusb/blob/master/docs/tutorial.rst#dealing-with-multiple-identical-devices), if there are two or more devices of the same vendor and the same model, you have to deal with "bus" and "address" attributes (you can see below how you can retrieve them), but it's not so clear how to use them to define a BrotherQLBackendPyUSB object.
+            # Anyway, you can find these attributes in the BrotherQLBackendPyUSB istance.
+
+            # PRINTER ATTRIBUTES (it's not so clear how to retrieve a list of all the possible attributes):
+            # print("device bus:", dev.bus)
+            # print("device address:", dev.address)
+            # print("device port:", dev.port_number)
+            # print("device speed:", dev.speed)
+
+            # to obtain the serial number, I changed the separator (from _ to /) and swapped two parameters.
+            serial = usb.util.get_string(dev, dev.iSerialNumber, 256)
+            return 'usb://0x{:04x}:0x{:04x}/{}'.format(dev.idVendor, dev.idProduct, serial)
         except:
             return 'usb://0x{:04x}:0x{:04x}'.format(dev.idVendor, dev.idProduct)
-
+        
     return [{'identifier': identifier(printer), 'instance': printer} for printer in printers]
 
 class BrotherQLBackendPyUSB(BrotherQLBackendGeneric):
@@ -67,7 +77,7 @@ def __init__(self, device_specifier):
 
         self.dev = None
         self.read_timeout =    10. # ms
-        self.write_timeout = 15000. # ms
+        self.write_timeout = 60000. # ms
         # strategy : try_twice or select
         self.strategy = 'try_twice'
         if isinstance(device_specifier, str):
@@ -78,7 +88,12 @@ def __init__(self, device_specifier):
             vendor, product = int(vendor, 16), int(product, 16)
             for result in list_available_devices():
                 printer = result['instance']
-                if printer.idVendor == vendor and printer.idProduct == product or (serial and printer.iSerialNumber == serial):
+                # quick and dirty approach to always use serial number. If it's not present: device not found
+                try:
+                    iSerialNumber = usb.util.get_string(printer, printer.iSerialNumber, 256)
+                except Exception:
+                    raise ValueError('Device not found')
+                if printer.idVendor == vendor and printer.idProduct == product and iSerialNumber == serial:
                     self.dev = printer
                     break
             if self.dev is None: