config: Nicer implementation of date parsing.

Keeps less local state through the function, to reduce the risk of that
state getting inconsistent.

oxrlib/config.py

@@ -48,27 +48,18 @@ class Configuration:
             post_hook()
 
     def _date_from_s(self, s):
-        number_digits = [[]]
+        clean_s = s.strip()
+        numbers = []
         seen_seps = set()
-        bad_c = False
-        for c in s.strip():
-            if c.isdigit():
-                number_digits[-1].append(c)
-            elif c in self.DATE_SEPS:
-                seen_seps.add(c)
-                number_digits.append([])
-            else:
-                bad_c = True
-        numbers = [int(''.join(digit_list), 10) for digit_list in number_digits]
-        if bad_c or (len(numbers) > 3) or (len(seen_seps) > 1):
+        start_index = 0
+        for index, c in (pair for pair in enumerate(clean_s) if pair[1] in self.DATE_SEPS):
+            seen_seps.add(c)
+            numbers.append(int(clean_s[start_index:index], 10))
+            start_index = index + 1
+        numbers.append(int(clean_s[start_index:], 10))
+        if (len(numbers) > 3) or (len(seen_seps) > 1):
             raise ValueError("can't parse date from {!r}".format(s))
-        replacements = {}
-        try:
-            replacements['day'] = numbers[-1]
-            replacements['month'] = numbers[-2]
-            replacements['year'] = numbers[-3]
-        except IndexError:
-            pass
+        replacements = dict(zip(['day', 'month', 'year'], reversed(numbers)))
         return self.TODAY.replace(**replacements)
 
     def _build_argparser(self):