spatialtime · May 14, 2024 18:55 · May 23, 2020 · May 12, 2020
diff --git a/iso8601_duration.py b/iso8601_duration.py
@@ -0,0 +1,73 @@
+# This snippet demonstrates Pythonic formatting and parsing of 
+# ISO 8601 durations.
+# A little work is required to navigate between Python's
+# timedelta syntax and ISO 8601 duration syntax.
+
+import re
+
+from datetime import datetime
+from datetime import timedelta
+
+def format_duration(td):
+    """Formats a timedelta instance into a correct ISO 8601 duration string.
+
+    Args:
+        td: a datetime.timedelta instance.
+    Returns:
+        a ISO 8601 duration string.
+    """
+
+    s = td.seconds 
+
+    ms = td.microseconds
+    if ms != 0:  # Round microseconds to milliseconds.
+        ms /= 1000000
+        ms = round(ms,3)
+        s += ms
+
+    return "P{}DT{}S".format(td.days,s)
+
+def parse_duration(iso_duration):
+    """Parses an ISO 8601 duration string into a datetime.timedelta instance.
+
+    Args:
+        iso_duration: an ISO 8601 duration string.
+    Returns:
+        a datetime.timedelta instance
+    """
+    m = re.match(r'^P(?:(\d+)Y)?(?:(\d+)M)?(?:(\d+)D)?T(?:(\d+)H)?(?:(\d+)M)?(?:(\d+(?:.\d+)?)S)?$',
+        iso_duration)
+    if m is None:
+        raise ValueError("invalid ISO 8601 duration string")
+
+    days = 0
+    hours = 0
+    minutes = 0
+    seconds = 0.0
+
+    # Years and months are not being utilized here, as there is not enough 
+    # information provided to determine which year and which month.
+    # Python's time_delta class stores durations as days, seconds and
+    # microseconds internally, and therefore we'd have to 
+    # convert parsed years and months to specific number of days.
+
+    if m[3]:
+        days = int(m[3])
+    if m[4]:
+        hours = int(m[4])
+    if m[5]:
+        minutes = int(m[5])
+    if m[6]:
+        seconds = float(m[6])
+
+    return timedelta(days=days, hours=hours, minutes=minutes, seconds=seconds)
+
+
+#example usage of format_duration()
+td = timedelta(seconds=10.2, milliseconds=322)
+iso_duration = format_duration(td)
+print(iso_duration)
+
+#example usage of parse_duration()
+print(parse_duration(iso_duration))
+