+ a quick fix

Author: skirpichev

Lib/fractions.py

@@ -247,23 +247,34 @@ def __new__(cls, numerator=0, denominator=None):
                         if _ and not exp:
                             raise ValueError
                         num, _, decimal = num.partition('.')
-                        if decimal:
-                            if num and num[0] in ('+', '-'):
+                        if num:
+                            if not num[-1].isdigit():
+                                raise ValueError
+                            if num[0] in ('+', '-'):
                                 sign = num[0] == '-'
                                 num = num[1:]
                             else:
                                 sign = 0
+                            if num and not num[0].isdigit():
+                                raise ValueError
+                        else:
+                            sign = 0
+                        if decimal:
+                            if not decimal[0].isdigit() or not decimal[-1].isdigit():
+                                raise ValueError
                             numerator = int(num or '0')
                             decimal_len = len(decimal.replace('_', ''))
                             decimal = int(decimal)
                             scale = 10**decimal_len
                             numerator = numerator*scale + decimal
                             denominator *= scale
-                            if sign:
-                                numerator = -numerator
                         else:
                             numerator = int(num)
+                        if sign:
+                            numerator = -numerator
                         if exp:
+                            if not (exp[0] in ('+', '-') or exp[0].isdigit()):
+                                raise ValueError
                             exp = int(exp)
                             if exp >= 0:
                                 numerator *= 10**exp

Lib/test/test_fractions.py

@@ -434,6 +434,7 @@ def check_invalid(s):
         # Imitate float's parsing.
         check_invalid("+ 3/2")
         check_invalid("- 3/2")
+        check_invalid("+ 343.33")
         # Avoid treating '.' as a regex special character.
         check_invalid("3a2")
         # Don't accept combinations of decimals and rationals.