python: add assumeFuture argument to flux.util.parse_datetime

Problem: The parse_datetime() utility function is statically configured
to assume future dates when a term like "Friday" is given. That is,
instead of giving the date for the previous Friday, the function will
return then next Friday instead. This behavior should be configurable.

Add an assumeFuture parameter to the function which defaults to True.
If set to False, then parse_datetime() will assume dates in the past
instead.

Author: grondo

src/bindings/python/flux/util.py

@@ -331,7 +331,7 @@ def parse_fsd(fsd_string):
     return seconds
 
 
-def parse_datetime(string, now=None):
+def parse_datetime(string, now=None, assumeFuture=True):
     """Parse a possibly human readable datetime string or offset
 
     If string starts with `+` or `-`, then the remainder of the string
@@ -369,6 +369,9 @@ def parse_datetime(string, now=None):
 
     cal = Calendar()
     cal.ptc.StartHour = 0
+    if not assumeFuture:
+        cal.ptc.DOWParseStyle = 0
+        cal.ptc.YearParseStyle = 0
     time_struct, status = cal.parse(string, sourceTime=now.timetuple())
     if status == 0:
         raise ValueError(f'Invalid datetime: "{string}"')