add dependency check for lp

src/escpos/printer/lp.py

@@ -8,69 +8,86 @@
 :license: MIT
 """
 
+import functools
 import os
 import subprocess
 import sys
 
 from ..escpos import Escpos
 
-if not sys.platform.startswith("win"):
 
-    class LP(Escpos):
-        """Simple UNIX lp command raw printing.
+def dependency_linux_lp(func):
+    """Indicate dependency on non Windows."""
 
-        Thanks to `Oyami-Srk comment <https://github.com/python-escpos/python-escpos/pull/348#issuecomment-549558316>`_.
-
-        inheritance:
-
-        .. inheritance-diagram:: escpos.printer.LP
-            :parts: 1
-
-        """
-
-        def __init__(self, printer_name: str, *args, **kwargs):
-            """LP class constructor.
-
-            :param printer_name: CUPS printer name (Optional)
-            :type printer_name: str
-            :param auto_flush: Automatic flush after every _raw() (Optional)
-            :type auto_flush: bool
-            """
-            Escpos.__init__(self, *args, **kwargs)
-            self.printer_name = printer_name
-            self.auto_flush = kwargs.get("auto_flush", True)
-            self.open()
-
-        def open(self):
-            """Invoke _lp_ in a new subprocess and wait for commands."""
-            self.lp = subprocess.Popen(
-                ["lp", "-d", self.printer_name, "-o", "raw"],
-                stdin=subprocess.PIPE,
-                stdout=open(os.devnull, "w"),
+    @functools.wraps(func)
+    def wrapper(*args, **kwargs):
+        """Throw a RuntimeError if not on a non-Windows system."""
+        if not sys.platform.startswith("win"):
+            raise RuntimeError(
+                "This printer driver depends on LP which is not"
+                "available on Windows systems."
             )
+        return func(*args, **kwargs)
 
-        def close(self):
-            """Stop the subprocess."""
-            self.lp.terminate()
+    return wrapper
 
-        def flush(self):
-            """End line and wait for new commands."""
-            if self.lp.stdin.writable():
-                self.lp.stdin.write(b"\n")
-            if self.lp.stdin.closed is False:
-                self.lp.stdin.close()
-            self.lp.wait()
-            self.open()
 
-        def _raw(self, msg):
-            """Write raw command(s) to the printer.
+class LP(Escpos):
+    """Simple UNIX lp command raw printing.
 
-            :param msg: arbitrary code to be printed
-            :type msg: bytes
-            """
-            if self.lp.stdin.writable():
-                self.lp.stdin.write(msg)
-            else:
-                raise Exception("Not a valid pipe for lp process")
-            if self.auto_flush:
-                self.flush()
+    Thanks to `Oyami-Srk comment <https://github.com/python-escpos/python-escpos/pull/348#issuecomment-549558316>`_.
+
+    inheritance:
+
+    .. inheritance-diagram:: escpos.printer.LP
+        :parts: 1
+
+    """
+
+    def __init__(self, printer_name: str, *args, **kwargs):
+        """LP class constructor.
+
+        :param printer_name: CUPS printer name (Optional)
+        :type printer_name: str
+        :param auto_flush: Automatic flush after every _raw() (Optional)
+        :type auto_flush: bool
+        """
+        Escpos.__init__(self, *args, **kwargs)
+        self.printer_name = printer_name
+        self.auto_flush = kwargs.get("auto_flush", True)
+        self.open()
+
+    @dependency_linux_lp
+    def open(self):
+        """Invoke _lp_ in a new subprocess and wait for commands."""
+        self.lp = subprocess.Popen(
+            ["lp", "-d", self.printer_name, "-o", "raw"],
+            stdin=subprocess.PIPE,
+            stdout=open(os.devnull, "w"),
+        )
+
+    def close(self):
+        """Stop the subprocess."""
+        self.lp.terminate()
+
+    def flush(self):
+        """End line and wait for new commands."""
+        if self.lp.stdin.writable():
+            self.lp.stdin.write(b"\n")
+        if self.lp.stdin.closed is False:
+            self.lp.stdin.close()
+        self.lp.wait()
+        self.open()
+
+    def _raw(self, msg):
+        """Write raw command(s) to the printer.
+
+        :param msg: arbitrary code to be printed
+        :type msg: bytes
+        """
+        if self.lp.stdin.writable():
+            self.lp.stdin.write(msg)
+        else:
+            raise Exception("Not a valid pipe for lp process")
+        if self.auto_flush:
+            self.flush()