GH9570 allow timedelta string conversion without leading zero

Author: chrisgilmerproj

doc/source/whatsnew/v0.16.1.txt

@@ -50,6 +50,8 @@ Enhancements
 - Allow conversion of values with dtype ``datetime64`` or ``timedelta64`` to strings using ``astype(str)`` (:issue:`9757`)
 - ``get_dummies`` function now accepts ``sparse`` keyword.  If set to ``True``, the return ``DataFrame`` is sparse, e.g. ``SparseDataFrame``. (:issue:`8823`)
 
+- Allow timedelta string conversion when leading zero is missing from time definition, ie `0:00:00` vs `00:00:00`. (:issue:`9570`)
+
 .. _whatsnew_0161.api:
 
 API changes

pandas/tseries/tests/test_timedeltas.py

@@ -64,6 +64,13 @@ def test_construction(self):
         self.assertEqual(Timedelta(123072001000000).value, 123072001000000)
         self.assertTrue('1 days 10:11:12.001' in str(Timedelta(123072001000000)))
 
+        # string conversion with/without leading zero
+        # GH 9570
+        self.assertEqual(Timedelta('0:00:00'), timedelta(hours=0))
+        self.assertEqual(Timedelta('00:00:00'), timedelta(hours=0))
+        self.assertEqual(Timedelta('-1:00:00'), -timedelta(hours=1))
+        self.assertEqual(Timedelta('-01:00:00'), -timedelta(hours=1))
+
         # more strings
         # GH 8190
         self.assertEqual(Timedelta('1 h'), timedelta(hours=1))

pandas/tseries/timedeltas.py

@@ -119,7 +119,7 @@ def _validate_timedelta_unit(arg):
 _short_search = re.compile(
     "^\s*(?P<neg>-?)\s*(?P<value>\d*\.?\d*)\s*(?P<unit>d|s|ms|us|ns)?\s*$",re.IGNORECASE)
 _full_search = re.compile(
-    "^\s*(?P<neg>-?)\s*(?P<days>\d*\.?\d*)?\s*(days|d|day)?,?\s*\+?(?P<time>\d{2}:\d{2}:\d{2})?(?P<frac>\.\d+)?\s*$",re.IGNORECASE)
+    "^\s*(?P<neg>-?)\s*(?P<days>\d*?\.?\d*?)?\s*(days|d|day)?,?\s*\+?(?P<time>\d{1,2}:\d{2}:\d{2})?(?P<frac>\.\d+)?\s*$",re.IGNORECASE)
 _nat_search = re.compile(
     "^\s*(nat|nan)\s*$",re.IGNORECASE)
 _whitespace = re.compile('^\s*$')
@@ -209,13 +209,12 @@ def convert(r=None, unit=None, m=m):
             is_neg = gd['neg']
             if gd['days']:
                 days = int((float(gd['days'] or 0) * 86400)*1e9)
-                if gd['neg']:
+                if is_neg:
                     days *= -1
                 value += days
             else:
-                if gd['neg']:
+                if is_neg:
                     value *= -1
-
             return tslib.cast_from_unit(value, 'ns')
         return convert