Add 'W' as a valid ISO 8601 designator

Author: mgmarino

pandas/_libs/tslibs/timedeltas.pyx

@@ -620,7 +620,7 @@ cdef inline int64_t parse_iso_format_string(str ts) except? -1:
             if not len(unit):
                 number.append(c)
             else:
-                if 'H' in unit or 'M' in unit:
+                if 'H' in unit or 'M' in unit or 'W' in unit:
                     if len(number) > 2:
                         raise ValueError(err_msg)
                 r = timedelta_from_spec(number, '0', unit)
@@ -636,7 +636,7 @@ cdef inline int64_t parse_iso_format_string(str ts) except? -1:
                     raise ValueError(err_msg)
                 else:
                     neg = 1
-            elif c in ['D', 'H', 'M']:
+            elif c in ['W', 'D', 'H', 'M']:
                 unit.append(c)
             elif c == '.':
                 # append any seconds

pandas/tests/scalar/timedelta/test_constructors.py

@@ -230,6 +230,7 @@ def test_overflow_on_construction():
         ("P1DT25H61M61S", Timedelta(days=1, hours=25, minutes=61, seconds=61)),
         ("PT1S", Timedelta(seconds=1)),
         ("PT0S", Timedelta(seconds=0)),
+        ("P1WT0S", Timedelta(days=7, seconds=0)),
     ],
 )
 def test_iso_constructor(fmt, exp):