Separate method open() and constructor, enhance consistency between connectors. (#584)

* Add self-open mechanism
* self-open mechanism through the 'device' property
* Separate open() and store connection in 'device'
* Restore device status to False on close()
* Add default value to all params + type annotations
* Add generic DeviceNotFoundError exception
* Update USBNotFoundError return code
* Enhance connectors consistency
* Fix LP printer stall
* Fix LP waste of paper due to auto-flush + flush on close
* Move platform dependent printers' guard to init

---------

Co-authored-by: Patrick Kanzler <4189642+patkan@users.noreply.github.com>

src/escpos/printer/network.py

@@ -8,9 +8,12 @@
 :license: MIT
 """
 
+import logging
 import socket
+from typing import Literal, Optional, Union
 
 from ..escpos import Escpos
+from ..exceptions import DeviceNotFoundError
 
 
 def is_usable() -> bool:
@@ -54,7 +57,14 @@ class Network(Escpos):
         """
         return is_usable()
 
-    def __init__(self, host, port=9100, timeout=60, *args, **kwargs):
+    def __init__(
+        self,
+        host: str = "",
+        port: int = 9100,
+        timeout: Union[int, float] = 60,
+        *args,
+        **kwargs,
+    ):
         """Initialize network printer.
 
         :param host:    Printer's host name or IP address
@@ -65,16 +75,40 @@ class Network(Escpos):
         self.host = host
         self.port = port
         self.timeout = timeout
-        self.open()
 
-    def open(self):
-        """Open TCP socket with ``socket``-library and set it as escpos device."""
-        self.device = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
-        self.device.settimeout(self.timeout)
-        self.device.connect((self.host, self.port))
+        self._device: Union[Literal[False], Literal[None], socket.socket] = False
 
-        if self.device is None:
-            print("Could not open socket for {0}".format(self.host))
+    def open(self, raise_not_found: bool = True) -> None:
+        """Open TCP socket with ``socket``-library and set it as escpos device.
+
+        By default raise an exception if device is not found.
+
+        :param raise_not_found: Default True.
+                                False to log error but do not raise exception.
+
+        :raises: :py:exc:`~escpos.exceptions.DeviceNotFoundError`
+        """
+        if self._device:
+            self.close()
+
+        try:
+            # Open device
+            self.device: Optional[socket.socket] = socket.socket(
+                socket.AF_INET, socket.SOCK_STREAM
+            )
+            self.device.settimeout(self.timeout)
+            self.device.connect((self.host, self.port))
+        except OSError as e:
+            # Raise exception or log error and cancel
+            self.device = None
+            if raise_not_found:
+                raise DeviceNotFoundError(
+                    f"Could not open socket for {self.host}:\n{e}"
+                )
+            else:
+                logging.error("Network device %s not found", self.host)
+                return
+        logging.info("Network printer enabled")
 
     def _raw(self, msg):
         """Print any command sent in raw format.
@@ -88,11 +122,14 @@ class Network(Escpos):
         """Read data from the TCP socket."""
         return self.device.recv(16)
 
-    def close(self):
+    def close(self) -> None:
         """Close TCP connection."""
-        if self.device is not None:
-            try:
-                self.device.shutdown(socket.SHUT_RDWR)
-            except socket.error:
-                pass
-            self.device.close()
+        if not self._device:
+            return
+        logging.info("Closing Network connection to printer %s", self.host)
+        try:
+            self._device.shutdown(socket.SHUT_RDWR)
+        except socket.error:
+            pass
+        self._device.close()
+        self._device = False