add wrapper that thros RuntimeError if not importable for pycups

src/escpos/printer/__init__.py

@@ -2,7 +2,7 @@
 """printer implementations."""
 
 # from .win32raw import Win32Raw
-# from .cups import CupsPrinter
+from .cups import CupsPrinter
 from .dummy import Dummy
 from .file import File
 from .lp import LP
@@ -17,7 +17,7 @@ __all__ = [
     "Serial",
     "LP",
     "Dummy",
-    # "CupsPrinter",
+    "CupsPrinter",
     # "Win32Raw",
 ]
 

src/escpos/printer/cups.py

@@ -8,19 +8,41 @@
 :license: MIT
 """
 
-from ..escpos import Escpos
-
-_CUPSPRINT = False
-try:
+import functools
 import tempfile
 
+from ..escpos import Escpos
+
+#: keeps track if the pycups dependency could be loaded (:py:class:`escpos.printer.CupsPrinter`)
+_DEP_PYCUPS = False
+
+try:
     import cups
 
-    _CUPSPRINT = True
+    _DEP_PYCUPS = True
 except ImportError:
     pass
 
-if _CUPSPRINT:
+
+# TODO: dev build mode that let's the wrapper bypass?
+
+
+def dependency_pycups(func):
+    """Indicate dependency on pycups."""
+
+    @functools.wraps(func)
+    def wrapper(*args, **kwargs):
+        """Throw a RuntimeError if pycups is not imported."""
+        if not _DEP_PYCUPS:
+            raise RuntimeError(
+                "Printing with PyCups requires the pycups library to"
+                "be installed. Please refer to the documentation on"
+                "what to install and install the dependencies for pycups."
+            )
+        return func(*args, **kwargs)
+
+    return wrapper
+
 
 class CupsPrinter(Escpos):
     """Simple CUPS printer connector.
@@ -38,6 +60,7 @@ if _CUPSPRINT:
 
     """
 
+    @dependency_pycups
     def __init__(self, printer_name=None, *args, **kwargs):
         """Class constructor for CupsPrinter.
 
@@ -94,6 +117,7 @@ if _CUPSPRINT:
             self.pending_job = False
             raise ValueError("Printer job not opened")
 
+    @dependency_pycups
     def send(self):
         """Send the print job to the printer."""
         if self.pending_job:

tox.ini

@@ -22,7 +22,6 @@ deps = jaconv
        pytest-mock
        hypothesis>4
        python-barcode
-       pycups
 commands = pytest
 passenv = ESCPOS_CAPABILITIES_PICKLE_DIR, ESCPOS_CAPABILITIES_FILE, CI, TRAVIS, TRAVIS_*, APPVEYOR, APPVEYOR_*, CODECOV_*
 setenv = PY_IGNORE_IMPORTMISMATCH=1