reworking the exception model

brother_ql/__init__.py

@@ -0,0 +1,6 @@
+
+class BrotherQLError(Exception): pass
+class BrotherQLUnsupportedCmd(BrotherQLError): pass
+class BrotherQLUnknownModel(BrotherQLError): pass
+class BrotherQLRasterError(BrotherQLError): pass
+

brother_ql/create.py

@@ -8,6 +8,7 @@ import numpy as np
 from PIL import Image
 
 from brother_ql.raster import BrotherQLRaster
+from brother_ql import BrotherQLError, BrotherQLUnsupportedCmd
 
 try:
     stdout = sys.stdout.buffer
@@ -36,6 +37,7 @@ def main():
     logging.basicConfig(level=args.loglevel)
 
     qlr = BrotherQLRaster(args.model)
+    qlr.exception_on_warning = True
     device_pixel_width = qlr.get_pixel_width()
 
     im = Image.open(args.image)
@@ -50,21 +52,36 @@ def main():
     arr[black_idx] = 0
 
 
-    qlr.add_switch_mode()
+    try:
+        qlr.add_switch_mode()
+    except BrotherQLUnsupportedCmd:
+        pass
     qlr.add_invalidate()
     qlr.add_initialize()
-    qlr.add_switch_mode()
+    try:
+        qlr.add_switch_mode()
+    except BrotherQLUnsupportedCmd:
+        pass
     qlr.mtype = 0x0A
     qlr.mwidth = 62
     qlr.mlength = 0
     qlr.add_media_and_quality(im.size[1])
-    qlr.add_autocut(True)
+    try:
-    qlr.add_cut_every(1)
+        qlr.add_autocut(True)
-    qlr.dpi_600 = False
+        qlr.add_cut_every(1)
-    qlr.cut_at_end = True
+    except BrotherQLUnsupportedCmd:
-    qlr.add_expanded_mode()
+        pass
+    try:
+        qlr.dpi_600 = False
+        qlr.cut_at_end = True
+        qlr.add_expanded_mode()
+    except BrotherQLUnsupportedCmd:
+        pass
     qlr.add_margins()
-    qlr.add_compression(True)
+    try:
+        qlr.add_compression(True)
+    except BrotherQLUnsupportedCmd:
+        pass
     qlr.add_raster_data(arr)
     qlr.add_print()
 

brother_ql/devicedependent.py

@@ -97,6 +97,8 @@ cuttingsupport = [
   'QL-720NW',
 ]
 
+expandedmode = cuttingsupport
+
 compressionsupport = [
   'QL-570',
   'QL-580N',

brother_ql/raster.py

@@ -13,15 +13,18 @@ from .devicedependent import models, \
                              right_margin_addition, \
                              compressionsupport, \
                              cuttingsupport, \
+                             expandedmode, \
                              modesetting
 
+from . import BrotherQLError, BrotherQLUnsupportedCmd, BrotherQLUnknownModel, BrotherQLRasterError
+
 logger = logging.getLogger(__name__)
 
 class BrotherQLRaster(object):
 
     def __init__(self, model='QL-500'):
         if model not in models:
-            raise BrotherQLRasterUnknownModel()
+            raise BrotherQLUnknownModel()
         self.model = model
         self.data = b''
         self._pquality = 1
@@ -31,12 +34,30 @@ class BrotherQLRaster(object):
         self._compression = False
         self.exception_on_warning = False
 
-    def warn(self, problem):
+    def _warn(self, problem, kind=BrotherQLRasterError):
+        """
+        Logs the warning message `problem` or raises a
+        `BrotherQLRasterError` exception (changeable via `kind`)
+        if `self.exception_on_warning` is set to True.
+
+        :raises BrotherQLRasterError: Or other exception \
+            set via the `kind` keyword argument.
+        """
         if self.exception_on_warning:
-            raise BrotherQLRasterError(problem)
+            raise kind(problem)
         else:
             logger.warning(problem)
 
+    def unsupported(self, problem):
+        """
+        Raises BrotherQLUnsupportedCmd if
+        exception_on_warning is set to True.
+        Issues a logger warning otherwise.
+
+        :raises BrotherQLUnsupportedCmd:
+        """
+        self._warn(problem, kind=BrotherQLUnsupportedCmd)
+
     def add_initialize(self):
         self.page_number = 0
         self.data += b'\x1B\x40' # init
@@ -48,7 +69,7 @@ class BrotherQLRaster(object):
         the mode change (others are in raster mode already).
         """
         if self.model not in modesetting:
-            self.warn("Trying to switch the operating mode on a printer that doesn't support the command.")
+            self.unsupported("Trying to switch the operating mode on a printer that doesn't support the command.")
             return
         self.data += b'\x1B\x69\x61\x01'
 
@@ -100,16 +121,22 @@ class BrotherQLRaster(object):
         # INFO:  media/quality (1B 69 7A) --> found! (payload: 8E 0A 3E 00 D2 00 00 00 00 00)
 
     def add_autocut(self, autocut = False):
+        if self.model not in cuttingsupport:
+            self.unsupported("Trying to call add_autocut with a printer that doesn't support it")
+            return
         self.data += b'\x1B\x69\x4D'
         self.data += bytes([autocut << 6])
 
     def add_cut_every(self, n=1):
+        if self.model not in cuttingsupport:
+            self.unsupported("Trying to call add_cut_every with a printer that doesn't support it")
+            return
         self.data += b'\x1B\x69\x41'
         self.data += bytes([n & 0xFF])
 
     def add_expanded_mode(self):
-        if self.model not in cuttingsupport:
+        if self.model not in expandedmode:
-            self.warn("Trying to set expanded mode on a printer that doesn't support it")
+            self.unsupported("Trying to set expanded mode (dpi/cutting at end) on a printer that doesn't support it")
             return
         self.data += b'\x1B\x69\x4B'
         flags = 0x00
@@ -123,7 +150,7 @@ class BrotherQLRaster(object):
 
     def add_compression(self, compression=True):
         if self.model not in compressionsupport:
-            self.warn("Trying to set compression on a printer that doesn't support it")
+            self.unsupported("Trying to set compression on a printer that doesn't support it")
             return
         self._compression = compression
         self.data += b'\x4D'
@@ -156,7 +183,3 @@ class BrotherQLRaster(object):
             self.data += b'\x1A'
         else:
             self.data += b'\x0C'
-
-class BrotherQLRasterError(Exception): pass
-class BrotherQLRasterUnknownModel(BrotherQLRasterError): pass
-