code: def parse_date(s):
      """parse an ISO8601 date string
  
      If it is None or not a valid ISO8601 timestamp,
      it will be returned unmodified.
      Otherwise, it will return a datetime object.
      """
      if s is None:
          return s
      m = ISO8601_PAT.match(s)
      if m:
          dt = _dateutil_parse(s)
          return _ensure_tzinfo(dt)
      return s
  
file_path: catboost/contrib/python/jupyter-client/py2/jupyter_client/jsonutil.py
imports: from datetime import datetime
  import re
  import warnings
  from dateutil.parser import parse
  from dateutil.tz import tzlocal
  from ipython_genutils import py3compat
  from ipython_genutils.py3compat import string_types, iteritems
label_desc: Use image node_id 2 for calling a global function with example usage: parse_date(s) and returns: s, s, _ensure_tzinfo