Add parsing of UTC time in ISO format

Author: hannes-ucsc

src/bd2k/util/__init__.py

@@ -1,10 +1,14 @@
 from __future__ import absolute_import
-from functools import wraps
-import pwd
+
+import datetime
 import grp
-import re
+import pwd
+from functools import wraps
+
 from threading import Lock
 
+import re
+
 
 def uid_to_name( uid ):
     return pwd.getpwuid( uid ).pw_name
@@ -168,6 +172,37 @@ def rfc3339_datetime_re( anchor=True ):
         ('$' if anchor else '') )
 
 
+_rfc3339_datetime_re = rfc3339_datetime_re( )
+
+
+def parse_iso_utc( s ):
+    """
+    Parses an ISO time with a hard-coded Z for zulu-time (UTC) at the end. Other timezones are
+    not supported.
+
+    :param str s: the ISO-formatted time
+
+    :rtype: datetime.datetime
+
+    :return: an timezone-naive datetime object
+
+    >>> parse_iso_utc('2016-04-27T00:28:04.000Z')
+    datetime.datetime(2016, 4, 27, 0, 28, 4)
+    >>> parse_iso_utc('2016-04-27T00:28:04Z')
+    datetime.datetime(2016, 4, 27, 0, 28, 4)
+    >>> parse_iso_utc('2016-04-27T00:28:04X')
+    Traceback (most recent call last):
+    ...
+    ValueError: Not a valid ISO datetime in UTC: 2016-04-27T00:28:04X
+    """
+    m = _rfc3339_datetime_re.match( s )
+    if not m:
+        raise ValueError( 'Not a valid ISO datetime in UTC: ' + s )
+    else:
+        fmt = '%Y-%m-%dT%H:%M:%S' + ('.%f' if m.group( 7 ) else '') + 'Z'
+        return datetime.datetime.strptime( s, fmt )
+
+
 def strict_bool( s ):
     """
     Variant of bool() that only accepts two possible string values.