Merge pull request #34 from saxbophone/josh/33-custom-error-classes

Create custom error classes

Author: saxbophone

basest/__init__.py

@@ -4,7 +4,7 @@
     absolute_import, division, print_function, unicode_literals
 )
 
-from . import core, encoders
+from . import core, encoders, exceptions
 
 
-__all__ = ['core', 'encoders']
+__all__ = ['core', 'encoders', 'exceptions']

basest/core/encode.py

@@ -4,6 +4,7 @@
     absolute_import, division, print_function, unicode_literals
 )
 
+from ..exceptions import ImproperUsageError
 from .utils import ints_to_symbols, symbols_to_ints, validate_symbol_tables
 
 
@@ -38,10 +39,10 @@ def encode_raw(input_base, output_base, input_ratio, output_ratio, input_data):
     Special validation: if the output base is larger than the input base, then
     the length of the input data MUST be an exact multiple of the input ratio.
     Otherwise, the data will be corrupted if we continue, so we will raise
-    ValueError instead.
+    ImproperUsageError instead.
     '''
     if input_base < output_base and input_length % input_ratio != 0:
-        raise ValueError(
+        raise ImproperUsageError(
             'Input data length must be exact multiple of input ratio when '
             'output base is larger than input base'
         )

basest/core/utils.py

@@ -4,6 +4,8 @@
     absolute_import, division, print_function, unicode_literals
 )
 
+from ..exceptions import InvalidSymbolTableError
+
 
 def ints_to_symbols(ints, symbol_table):
     """
@@ -39,12 +41,12 @@ def validate_symbol_tables(symbol_table, padding_symbol, other_symbol_table):
     """
     Validates two symbol tables (the padding symbol being used alongside the
     first one).
-    Raises ValueError if either of the symbol tables (or padding symbol) fail
-    validation.
+    Raises InvalidSymbolTableError if either of the symbol tables (or padding
+    symbol) fail validation.
     """
     # first check that they all do not contain None
     if None in (symbol_table + [padding_symbol] + other_symbol_table):
-        raise ValueError(
+        raise InvalidSymbolTableError(
             'None cannot be used in symbol tables nor for padding'
         )
     # if that check passes, validate tables (and padding) for uniqueness
@@ -53,4 +55,4 @@ def validate_symbol_tables(symbol_table, padding_symbol, other_symbol_table):
         (not _symbol_table_is_unique(symbol_table, padding_symbol)) or
         (not _symbol_table_is_unique(other_symbol_table))
     ):
-        raise ValueError('Unique symbol tables required')
+        raise InvalidSymbolTableError('Unique symbol tables required')

basest/exceptions.py

@@ -0,0 +1,21 @@
+#!/usr/bin/python
+# -*- coding: utf-8 -*-
+
+
+class ImproperUsageError(ValueError):
+    """
+    This exception is raised when an attempt is made to encode data using a
+    larger output base than the input base AND when the length of the input
+    data is not exactly divisible by the input ratio.
+
+    This cannot be allowed because such options would cause data corruption.
+    """
+    pass
+
+
+class InvalidSymbolTableError(ValueError):
+    """
+    This exception is raised when the symbol table and/or padding symbol
+    supplied to an encoding/decoding operation are invalid.
+    """
+    pass

tests/core/test_encode_decode.py

@@ -9,6 +9,7 @@
 from ddt import data, ddt, unpack
 
 from basest.core import decode, encode
+from basest.exceptions import InvalidSymbolTableError
 
 
 base64_alphabet = [
@@ -140,9 +141,9 @@ def test_encode_rejects_non_unique_symbol_tables(
     ):
         """
         When a non-unique input or output symbol table is passed to encode(),
-        ValueError should be raised.
+        InvalidSymbolTableError should be raised.
         """
-        with self.assertRaises(ValueError):
+        with self.assertRaises(InvalidSymbolTableError):
             encode(
                 len(input_symbol_table), input_symbol_table,
                 len(output_symbol_table), output_symbol_table,
@@ -156,9 +157,9 @@ def test_encode_rejects_output_symbol_table_containing_padding_symbol(
     ):
         """
         When the output symbol table passed to encode() contains the padding
-        symbol, ValueError should be raised.
+        symbol, InvalidSymbolTableError should be raised.
         """
-        with self.assertRaises(ValueError):
+        with self.assertRaises(InvalidSymbolTableError):
             encode(1, ['a'], 1, ['b'], 'b', 1, 1, [])
 
     @data(
@@ -175,9 +176,9 @@ def test_encode_rejects_none_used_in_symbol_tables_and_padding(
     ):
         """
         When any of the symbol tables or the padding symbol passed to encode()
-        are or contain None, ValueError should be raised.
+        are or contain None, InvalidSymbolTableError should be raised.
         """
-        with self.assertRaises(ValueError):
+        with self.assertRaises(InvalidSymbolTableError):
             encode(
                 len(input_symbol_table), input_symbol_table,
                 len(output_symbol_table), output_symbol_table,
@@ -294,9 +295,9 @@ def test_decode_rejects_non_unique_symbol_tables(
     ):
         """
         When a non-unique input or output symbol table is passed to decode(),
-        ValueError should be raised.
+        InvalidSymbolTableError should be raised.
         """
-        with self.assertRaises(ValueError):
+        with self.assertRaises(InvalidSymbolTableError):
             decode(
                 len(input_symbol_table), input_symbol_table,
                 padding_symbol,
@@ -310,9 +311,9 @@ def test_decode_rejects_input_symbol_table_containing_padding_symbol(
     ):
         """
         When the input symbol table passed to decode() contains the padding
-        symbol, ValueError should be raised.
+        symbol, InvalidSymbolTableError should be raised.
         """
-        with self.assertRaises(ValueError):
+        with self.assertRaises(InvalidSymbolTableError):
             decode(1, ['a'], 'a', 1, ['b'], 1, 1, [])
 
     @data(
@@ -329,9 +330,9 @@ def test_decode_rejects_none_used_in_symbol_tables_and_padding(
     ):
         """
         When any of the symbol tables or the padding symbol passed to decode()
-        are or contain None, ValueError should be raised.
+        are or contain None, InvalidSymbolTableError should be raised.
         """
-        with self.assertRaises(ValueError):
+        with self.assertRaises(InvalidSymbolTableError):
             decode(
                 len(input_symbol_table), input_symbol_table,
                 padding_symbol,

tests/core/test_encode_decode_raw.py

@@ -9,6 +9,7 @@
 from ddt import data, ddt, unpack
 
 from basest.core import decode_raw, encode_raw
+from basest.exceptions import ImproperUsageError
 
 
 @ddt
@@ -80,9 +81,9 @@ def test_encode_raw_invalid_input_ratio(
         input ratio. This is because such an action normally can be solved with
         padding, however padding can only be used successfully on the 'smaller'
         side of the transformation, in any other case data corruption occurs.
-        If this is attempted, then ValueError should be raised.
+        If this is attempted, then ImproperUsageError should be raised.
         """
-        with self.assertRaises(ValueError):
+        with self.assertRaises(ImproperUsageError):
             encode_raw(
                 input_base=input_base, output_base=output_base,
                 input_ratio=input_ratio, output_ratio=output_ratio,