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/serial.py

@@ -0,0 +1,153 @@
+#!/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
+
+from ..escpos import Escpos
+
+#: keeps track if the pyserial dependency could be loaded (:py:class:`escpos.printer.Serial`)
+_DEP_PYSERIAL = False
+
+try:
+    import serial
+
+    _DEP_PYSERIAL = True
+except ImportError:
+    pass
+
+
+def is_usable() -> bool:
+    """Indicate whether this component can be used due to dependencies."""
+    usable = False
+    if _DEP_PYSERIAL:
+        usable = True
+    return usable
+
+
+def dependency_pyserial(func):
+    """Indicate dependency on pyserial."""
+
+    @functools.wraps(func)
+    def wrapper(*args, **kwargs):
+        """Throw a RuntimeError if pyserial not installed."""
+        if not is_usable():
+            raise RuntimeError(
+                "Printing with Serial requires the pyserial library to"
+                "be installed. Please refer to the documentation on"
+                "what to install and install the dependencies for pyserial."
+            )
+        return func(*args, **kwargs)
+
+    return wrapper
+
+
+class Serial(Escpos):
+    """Serial printer.
+
+    This class describes a printer that is connected by serial interface.
+
+    inheritance:
+
+    .. inheritance-diagram:: escpos.printer.Serial
+        :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()
+
+    @dependency_pyserial
+    def __init__(
+        self,
+        devfile="/dev/ttyS0",
+        baudrate=9600,
+        bytesize=8,
+        timeout=1,
+        parity=None,
+        stopbits=None,
+        xonxoff=False,
+        dsrdtr=True,
+        *args,
+        **kwargs
+    ):
+        """Initialize serial printer.
+
+        :param devfile:  Device file under dev filesystem
+        :param baudrate: Baud rate for serial transmission
+        :param bytesize: Serial buffer size
+        :param timeout:  Read/Write timeout
+        :param parity:   Parity checking
+        :param stopbits: Number of stop bits
+        :param xonxoff:  Software flow control
+        :param dsrdtr:   Hardware flow control (False to enable RTS/CTS)
+        """
+        Escpos.__init__(self, *args, **kwargs)
+        self.devfile = devfile
+        self.baudrate = baudrate
+        self.bytesize = bytesize
+        self.timeout = timeout
+        if parity:
+            self.parity = parity
+        else:
+            self.parity = serial.PARITY_NONE
+        if stopbits:
+            self.stopbits = stopbits
+        else:
+            self.stopbits = serial.STOPBITS_ONE
+        self.xonxoff = xonxoff
+        self.dsrdtr = dsrdtr
+
+        self.open()
+
+    @dependency_pyserial
+    def open(self):
+        """Set up serial port and set is as escpos device."""
+        if self.device is not None and self.device.is_open:
+            self.close()
+        self.device = serial.Serial(
+            port=self.devfile,
+            baudrate=self.baudrate,
+            bytesize=self.bytesize,
+            parity=self.parity,
+            stopbits=self.stopbits,
+            timeout=self.timeout,
+            xonxoff=self.xonxoff,
+            dsrdtr=self.dsrdtr,
+        )
+
+        if self.device is not None:
+            print("Serial printer enabled")
+        else:
+            print("Unable to open serial printer on: {0}".format(str(self.devfile)))
+
+    def _raw(self, msg):
+        """Print any command sent in raw format.
+
+        :param msg: arbitrary code to be printed
+        :type msg: bytes
+        """
+        self.device.write(msg)
+
+    def _read(self):
+        """Read the data buffer and return it to the caller."""
+        return self.device.read(16)
+
+    def close(self):
+        """Close Serial interface."""
+        if self.device is not None and self.device.is_open:
+            self.device.flush()
+            self.device.close()