Drop Py37, improve typing and docstrings (#544)

Drops Py3.7, improves typing and adds a mypy config, improves the docstrings and isorts the imports.

* configure isort
* sort with isort
* add github action
* enable flake8-docstrings
* fix docstrings
* add mypy env
* no implicit optional
* add type for raw
* add some type hints

src/escpos/exceptions.py

@@ -1,5 +1,5 @@
 #  -*- coding: utf-8 -*-
-""" ESC/POS Exceptions classes
+"""ESC/POS Exceptions classes.
 
 Result/Exit codes:
 
@@ -27,9 +27,10 @@ Result/Exit codes:
 
 
 class Error(Exception):
-    """Base class for ESC/POS errors"""
+    """Base class for ESC/POS errors."""
 
     def __init__(self, msg, status=None):
+        """Initialize Error object."""
         Exception.__init__(self)
         self.msg = msg
         self.resultcode = 1
@@ -37,6 +38,7 @@ class Error(Exception):
             self.resultcode = status
 
     def __str__(self):
+        """Return string representation of Error."""
         return self.msg
 
 
@@ -49,11 +51,13 @@ class BarcodeTypeError(Error):
     """
 
     def __init__(self, msg=""):
+        """Initialize BarcodeTypeError object."""
         Error.__init__(self, msg)
         self.msg = msg
         self.resultcode = 10
 
     def __str__(self):
+        """Return string representation of BarcodeTypeError."""
         return "No Barcode type is defined ({msg})".format(msg=self.msg)
 
 
@@ -66,11 +70,13 @@ class BarcodeSizeError(Error):
     """
 
     def __init__(self, msg=""):
+        """Initialize BarcodeSizeError object."""
         Error.__init__(self, msg)
         self.msg = msg
         self.resultcode = 20
 
     def __str__(self):
+        """Return string representation of BarcodeSizeError."""
         return "Barcode size is out of range ({msg})".format(msg=self.msg)
 
 
@@ -83,11 +89,13 @@ class BarcodeCodeError(Error):
     """
 
     def __init__(self, msg=""):
+        """Initialize BarcodeCodeError object."""
         Error.__init__(self, msg)
         self.msg = msg
         self.resultcode = 30
 
     def __str__(self):
+        """Return string representation of BarcodeCodeError."""
         return "No Barcode code was supplied ({msg})".format(msg=self.msg)
 
 
@@ -98,11 +106,13 @@ class ImageSizeError(Error):
     """
 
     def __init__(self, msg=""):
+        """Initialize ImageSizeError object."""
         Error.__init__(self, msg)
         self.msg = msg
         self.resultcode = 40
 
     def __str__(self):
+        """Return string representation of ImageSizeError."""
         return "Image height is longer than 255px and can't be printed ({msg})".format(
             msg=self.msg
         )
@@ -115,11 +125,13 @@ class ImageWidthError(Error):
     """
 
     def __init__(self, msg=""):
+        """Initialize ImageWidthError object."""
         Error.__init__(self, msg)
         self.msg = msg
         self.resultcode = 41
 
     def __str__(self):
+        """Return string representation of ImageWidthError."""
         return "Image width is too large ({msg})".format(msg=self.msg)
 
 
@@ -131,11 +143,13 @@ class TextError(Error):
     """
 
     def __init__(self, msg=""):
+        """Initialize TextError object."""
         Error.__init__(self, msg)
         self.msg = msg
         self.resultcode = 50
 
     def __str__(self):
+        """Return string representation of TextError."""
         return "Text string must be supplied to the text() method ({msg})".format(
             msg=self.msg
         )
@@ -149,16 +163,20 @@ class CashDrawerError(Error):
     """
 
     def __init__(self, msg=""):
+        """Initialize CashDrawerError object."""
         Error.__init__(self, msg)
         self.msg = msg
         self.resultcode = 60
 
     def __str__(self):
+        """Return string representation of CashDrawerError."""
         return "Valid pin must be set to send pulse ({msg})".format(msg=self.msg)
 
 
 class TabPosError(Error):
-    """Valid tab positions must be set by using from 1 to 32 tabs, and between 1 and 255 tab size values.
+    """Tab position is invalid.
+
+    Valid tab positions must be set by using from 1 to 32 tabs, and between 1 and 255 tab size values.
     Both values multiplied must not exceed 255, since it is the maximum tab value.
 
     This exception is raised by :py:meth:`escpos.escpos.Escpos.control`.
@@ -166,11 +184,13 @@ class TabPosError(Error):
     """
 
     def __init__(self, msg=""):
+        """Initialize TabPosError object."""
         Error.__init__(self, msg)
         self.msg = msg
         self.resultcode = 70
 
     def __str__(self):
+        """Return string representation of TabPosError."""
         return "Valid tab positions must be in the range 0 to 16 ({msg})".format(
             msg=self.msg
         )
@@ -184,43 +204,49 @@ class CharCodeError(Error):
     """
 
     def __init__(self, msg=""):
+        """Initialize CharCodeError object."""
         Error.__init__(self, msg)
         self.msg = msg
         self.resultcode = 80
 
     def __str__(self):
+        """Return string representation of CharCodeError."""
         return "Valid char code must be set ({msg})".format(msg=self.msg)
 
 
 class USBNotFoundError(Error):
-    """Device wasn't found (probably not plugged in)
+    """Device wasn't found (probably not plugged in).
 
     The USB device seems to be not plugged in.
     Ths returncode for this exception is `90`.
     """
 
     def __init__(self, msg=""):
+        """Initialize USBNotFoundError object."""
         Error.__init__(self, msg)
         self.msg = msg
         self.resultcode = 90
 
     def __str__(self):
+        """Return string representation of USBNotFoundError."""
         return "USB device not found ({msg})".format(msg=self.msg)
 
 
 class SetVariableError(Error):
-    """A set method variable was out of range
+    """A set method variable was out of range.
 
     Check set variables against minimum and maximum values
     Ths returncode for this exception is `100`.
     """
 
     def __init__(self, msg=""):
+        """Initialize SetVariableError object."""
         Error.__init__(self, msg)
         self.msg = msg
         self.resultcode = 100
 
     def __str__(self):
+        """Return string representation of SetVariableError."""
         return "Set variable out of range ({msg})".format(msg=self.msg)
 
 
@@ -228,48 +254,54 @@ class SetVariableError(Error):
 
 
 class ConfigNotFoundError(Error):
-    """The configuration file was not found
+    """The configuration file was not found.
 
     The default or passed configuration file could not be read
     Ths returncode for this exception is `200`.
     """
 
     def __init__(self, msg=""):
+        """Initialize ConfigNotFoundError object."""
         Error.__init__(self, msg)
         self.msg = msg
         self.resultcode = 200
 
     def __str__(self):
+        """Return string representation of ConfigNotFoundError."""
         return "Configuration not found ({msg})".format(msg=self.msg)
 
 
 class ConfigSyntaxError(Error):
-    """The configuration file is invalid
+    """The configuration file is invalid.
 
     The syntax is incorrect
     Ths returncode for this exception is `210`.
     """
 
     def __init__(self, msg=""):
+        """Initialize ConfigSyntaxError object."""
         Error.__init__(self, msg)
         self.msg = msg
         self.resultcode = 210
 
     def __str__(self):
+        """Return string representation of ConfigSyntaxError."""
         return "Configuration syntax is invalid ({msg})".format(msg=self.msg)
 
 
 class ConfigSectionMissingError(Error):
-    """The configuration file is missing a section
+    """The configuration file is missing a section.
 
     The part of the config asked for doesn't exist in the loaded configuration
     Ths returncode for this exception is `220`.
     """
 
     def __init__(self, msg=""):
+        """Initialize ConfigSectionMissingError object."""
         Error.__init__(self, msg)
         self.msg = msg
         self.resultcode = 220
 
     def __str__(self):
+        """Return string representation of ConfigSectionMissingError."""
         return "Configuration section is missing ({msg})".format(msg=self.msg)