split off dependencies for optional installation (#546)

* add inheritance diagrams to all printers and exceptions
* split off printer implementations into separate files
* add wrapper that thros RuntimeError if not importable
* add dependency check for lp
* add dependency check for pyserial
* added check for usability
* import Win32Raw
* include WIn32Raw in documentation
* enable all extras on tox
* update github workflow

src/escpos/printer/lp.py

@@ -0,0 +1,110 @@
+#!/usr/bin/python
+#  -*- coding: utf-8 -*-
+"""This module contains the implementation of the CupsPrinter printer driver.
+
+:author: python-escpos developers
+:organization: `python-escpos <https://github.com/python-escpos>`_
+:copyright: Copyright (c) 2012-2023 Bashlinux and python-escpos
+:license: MIT
+"""
+
+import functools
+import os
+import subprocess
+import sys
+
+from ..escpos import Escpos
+
+
+def is_usable() -> bool:
+    """Indicate whether this component can be used due to dependencies."""
+    usable = False
+    if sys.platform.startswith("win"):
+        usable = True
+    return usable
+
+
+def dependency_linux_lp(func):
+    """Indicate dependency on non Windows."""
+
+    @functools.wraps(func)
+    def wrapper(*args, **kwargs):
+        """Throw a RuntimeError if not on a non-Windows system."""
+        if not is_usable():
+            raise RuntimeError(
+                "This printer driver depends on LP which is not"
+                "available on Windows systems."
+            )
+        return func(*args, **kwargs)
+
+    return wrapper
+
+
+class LP(Escpos):
+    """Simple UNIX lp command raw printing.
+
+    Thanks to `Oyami-Srk comment <https://github.com/python-escpos/python-escpos/pull/348#issuecomment-549558316>`_.
+
+    inheritance:
+
+    .. inheritance-diagram:: escpos.printer.LP
+        :parts: 1
+
+    """
+
+    @staticmethod
+    def is_usable() -> bool:
+        """Indicate whether this printer class is usable.
+
+        Will return True if dependencies are available.
+        Will return False if not.
+        """
+        return is_usable()
+
+    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()