Wrote code to make failing tests pass

Author: saxbophone

basest/core/decode.py

@@ -5,7 +5,7 @@
 )
 
 from .encode import encode_raw
-from .utils import ints_to_symbols, symbols_to_ints
+from .utils import ints_to_symbols, symbol_table_is_unique, symbols_to_ints
 
 
 def decode_raw(input_base, output_base, input_ratio, output_ratio, input_data):
@@ -54,6 +54,12 @@ def decode(
     Assumes standard base64-style padding using the given input padding symbol,
     but can handle unpadded input just fine.
     """
+    # validate the uniqueness of both symbol tables before continuing
+    if (
+        (not symbol_table_is_unique(input_symbol_table, input_padding)) or
+        (not symbol_table_is_unique(output_symbol_table))
+    ):
+        raise ValueError('Unique symbol tables required')
     # create workon copy of input data and convert symbols to raw ints
     # NOTE: input symbol table here includes the padding character
     input_workon = symbols_to_ints(

basest/core/encode.py

@@ -4,7 +4,7 @@
     absolute_import, division, print_function, unicode_literals
 )
 
-from .utils import ints_to_symbols, symbols_to_ints
+from .utils import ints_to_symbols, symbol_table_is_unique, symbols_to_ints
 
 
 def _nearest_length(input_length, input_ratio):
@@ -96,6 +96,12 @@ def encode(
     Uses standard base64-style padding if needed, using the given padding
     symbol.
     """
+    # validate the uniqueness of both symbol tables before continuing
+    if (
+        (not symbol_table_is_unique(input_symbol_table)) or
+        (not symbol_table_is_unique(output_symbol_table, output_padding))
+    ):
+        raise ValueError('Unique symbol tables required')
     # create workon copy of input data and convert symbols to raw ints
     input_workon = symbols_to_ints(input_data, input_symbol_table)
     # use encode_raw() to encode the data

basest/core/utils.py

@@ -19,3 +19,17 @@ def symbols_to_ints(symbols, symbol_table):
     convert them to an iterable of ints and return this.
     """
     return [symbol_table.index(s) for s in symbols]
+
+
+def symbol_table_is_unique(symbol_table, padding_symbol=None):
+    """
+    Returns True if the given symbol table and padding symbol are unique,
+    otherwise returns False.
+    """
+    # simple way of checking if a list of hashables is unique
+    if len(symbol_table) != len(set(symbol_table)):
+        return False
+    else:
+        # otherwise, check that padding_symbol isn't in the symbol table
+        # NOTE: this assumes that `None` is never in the symbol table
+        return padding_symbol not in symbol_table