Allow specifying time intervals for start_time and end_time

Change defaults in sample configspec.conf to have a woring example.

seiscat/conf/configspec.conf

@@ -27,16 +27,18 @@ extra_field_defaults = force_list(default=None)
 ## FDSN event webservice URL or shortcut
 # It can be an ObsPy supported shortcut (ex., ISC, USGS, RESIF)
 # or a full URL (ex., http://www.isc.ac.uk/fdsnws/event/1/)
-fdsn_event_url = string(default=ISC)
+fdsn_event_url = string(default=USGS)
 
 
 ## Event selection criteria
 ## Use "None" to signify no limit
-# Start time for event selection (UTC date time or None)
+# Start time for event selection (UTC date time, time interval or None)
 # ex.: start_time = 2021-08-23T00:00:00
-start_time = string(default=None)
-# End time for event selection (UTC date time or None)
+# ex.: start_time = -10 days
+start_time = string(default="-1 day")
+# End time for event selection (UTC date time, time interval or None)
 # ex.: end_time = 2021-08-24T00:00:00
+# ex.: end_time = -1 hour
 end_time = string(default=None)
 # Recheck period (string or None).
 # Use a string with the format "X unit" where X is an integer and unit is

seiscat/fdsnws.py

@@ -34,7 +34,21 @@ def _to_utc_datetime(time):
  :param time: time in string format
  :returns: UTCDateTime object or None
  """
- return None if time is None else UTCDateTime(time)
+ if time is None:
+ return None
+ try:
+ return UTCDateTime(time)
+ except TypeError:
+ try:
+ time_interval = _parse_time_interval(time)
+ return UTCDateTime() + time_interval
+ except ValueError as e:
+ raise ValueError(
+ f'Invalid time format: {time}.\n'
+ 'Please use YYYY-MM-DDTHH:MM:SS or '
+ 'a time interval (typically in the past),\n'
+ 'e.g., -1 day, -2 hours, -5 minutes, -10 seconds.'
+ ) from e
 
 
 def _parse_time_interval(time_interval):
@@ -50,25 +64,24 @@ def _parse_time_interval(time_interval):
  value = int(parts[0])
  unit = parts[1]
  if unit.endswith('s'):
+ # remvove plural form
  unit = unit[:-1]
  if unit == 'day':
  return timedelta(days=value)
- elif unit == 'hour':
+ if unit == 'hour':
  return timedelta(hours=value)
- elif unit == 'minute':
+ if unit == 'minute':
  return timedelta(minutes=value)
- elif unit == 'second':
+ if unit == 'second':
  return timedelta(seconds=value)
- else:
- raise ValueError(f'Invalid time unit: {unit}')
+ raise ValueError(f'Invalid time unit: {unit}')
 
 
 class InvalidQuery(Exception):
  """Invalid query exception."""
- pass
 
 
-class QueryArgs(object):
+class QueryArgs():
  """Build query arguments for FDSN client."""
  def __init__(self, config, suffix, first_query):
  """