Fix grammar table for verbs

Verbs have multiple grammar tables in duden sometimes each with
different number of keys for each grammar form, since there are special
forms such as 'infinitiv mit zu' where normal categories such as
singular and plural do not apply.

This commit fixes the table by adding padding to rows with less keys.

Fixes #94.

duden/main.py

@@ -675,21 +675,34 @@ def display_grammar(word, grammar_args):
 
     grammar_tokens = [token.lower() for token in grammar_args.split(',')]
 
-    table = []
+    # filter out grammar forms which do not match provided keys
+    tag_columns = []
+    value_column = []
     for keys, value in word.grammar_raw:
         lkeys = {key.lower() for key in keys}
 
         if not (grammar_args == 'ALL' or lkeys.issuperset(grammar_tokens)):
             continue
 
         reduced_keys = lkeys.difference(grammar_tokens)
-        keystring = ' '.join(reduced_keys)
 
-        if keystring:
-            row = list(reduced_keys) + [blue("|"), value]
-        else:
-            row = [value]
+        tag_columns.append(list(reduced_keys))
+        value_column.append(value)
+
+    # determine the width of the table
+    max_keys_count = max(map(len, tag_columns))
+
+    # if provided keys uniquely determine the value(s), display a 1-col table
+    if max_keys_count == 0:
+        return display_table([[value] for value in value_column])
+
+    # otherwise make a nice "| key1 key2 | value |" table
+    table = []
+    for keys, value in zip(tag_columns, value_column):
+        padding = [""] * (max_keys_count - len(keys))
+        row = keys + padding + [blue("|")] + [value]
         table.append(row)
+
     display_table(table)