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Python and ISO 8601 durations
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# 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)) | |
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Thank you. Great lib.