Specify explicit cause/context for exceptions

Author: WhyNotHugo

barcode/__init__.py

@@ -71,8 +71,8 @@ def get(name, code=None, writer=None, options=None):
     options = options or {}
     try:
         barcode = __BARCODE_MAP[name.lower()]
-    except KeyError:
-        raise BarcodeNotFoundError(f"The barcode {name!r} you requested is not known.")
+    except KeyError as e:
+        raise BarcodeNotFoundError(f"The barcode {name!r} is not known.") from e
     if code is not None:
         return barcode(code, writer, **options)
     else:

barcode/codabar.py

@@ -46,19 +46,21 @@ def build(self):
             )  # Start with [A-D], followed by a narrow space
 
         except KeyError:
-            raise BarcodeError("Codabar should start with either A,B,C or D")
+            raise BarcodeError("Codabar should start with either A,B,C or D") from None
 
         try:
             data += "n".join(
                 [codabar.CODES[c] for c in self.code[1:-1]]
             )  # separated by a narrow space
         except KeyError:
-            raise IllegalCharacterError("Codabar can only contain numerics or $:/.+-")
+            raise IllegalCharacterError(
+                "Codabar can only contain numerics or $:/.+-"
+            ) from None
 
         try:
             data += "n" + codabar.STARTSTOP[self.code[-1]]  # End with [A-D]
         except KeyError:
-            raise BarcodeError("Codabar should end with either A,B,C or D")
+            raise BarcodeError("Codabar should end with either A,B,C or D") from None
 
         raw = ""
         for e in data: