Feature(escpos) Add buzzer function (#535)

* Add buzzer function
* Add `buzzer(time, duration)` function to control the buzzer on supported
   printers.
* Add unit tests for buzzer function.
* Update test_function_buzzer.py to pass black
* Run black in tests files
---------

Co-authored-by: Patrick Kanzler <dev@pkanzler.de>

src/escpos/constants.py

@@ -63,6 +63,9 @@ PAPER_PART_CUT = _CUT_PAPER(b"\x01")  #: Partial cut paper
 # Beep (please note that the actual beep sequence may differ between devices)
 BEEP = b"\x07"
 
+# Internal buzzer (only supported printers)
+BUZZER = ESC + b"\x42"
+
 # Panel buttons (e.g. the FEED button)
 _PANEL_BUTTON = lambda n: ESC + b"c5" + six.int2byte(n)
 PANEL_BUTTON_ON = _PANEL_BUTTON(0)  # enable all panel buttons

src/escpos/escpos.py

@@ -58,6 +58,7 @@ from .constants import (
     CD_KICK_2,
     PAPER_FULL_CUT,
     PAPER_PART_CUT,
+    BUZZER,
 )
 from .constants import HW_RESET, HW_SELECT, HW_INIT
 from .constants import (
@@ -1243,6 +1244,24 @@ class Escpos(object):
         """
         self._raw(SLIP_SELECT)
 
+    def buzzer(self, times=2, duration=4):
+        """Activate the internal printer buzzer (only supported printers).
+
+        The 'times' parameter refers to the 'n' escpos command parameter,
+        which means how many times the buzzer will be 'beeped'.
+
+        :param times: Integer between 1 and 9, indicates the buzzer beeps.
+        :param duration: Integer between 1 and 9, indicates the beep duration.
+        :returns: None
+        """
+
+        if not 1 <= times <= 9:
+            raise ValueError("times must be between 1 and 9")
+        if not 1 <= duration <= 9:
+            raise ValueError("duration must be between 1 and 9")
+
+        self._raw(BUZZER + six.int2byte(times) + six.int2byte(duration))
+
 
 class EscposIO(object):
     """ESC/POS Printer IO object