Backport parsedate_to_datetime() to py2

Or at least hopping so...

wifiwithme/apps/contribmap/migrations/0007_auto_20160303_1326.py

@@ -1,7 +1,11 @@
 # -*- coding: utf-8 -*-
 # Generated by Django 1.9.3 on 2016-03-03 13:26
 from __future__ import unicode_literals
-from email.utils import parsedate_to_datetime
+
+try:
+    from email.utils import parsedate_to_datetime
+except ImportError:  # py2
+    from wifiwithme.core.py2_compat import parsedate_to_datetime
 
 from django.db import migrations
 from django.utils.timezone import make_aware

wifiwithme/core/py2_compat.py

@@ -0,0 +1,128 @@
+import datetime
+from email._parseaddr import _daynames, _monthnames, _timezones
+
+
+def _parsedate_tz(data):
+    """Convert date to extended time tuple.
+
+    The last (additional) element is the time zone offset in seconds, except if
+    the timezone was specified as -0000.  In that case the last element is
+    None.  This indicates a UTC timestamp that explicitly declaims knowledge of
+    the source timezone, as opposed to a +0000 timestamp that indicates the
+    source timezone really was UTC.
+
+    """
+    if not data:
+        return
+    data = data.split()
+    # The FWS after the comma after the day-of-week is optional, so search and
+    # adjust for this.
+    if data[0].endswith(',') or data[0].lower() in _daynames:
+        # There's a dayname here. Skip it
+        del data[0]
+    else:
+        i = data[0].rfind(',')
+        if i >= 0:
+            data[0] = data[0][i+1:]
+    if len(data) == 3: # RFC 850 date, deprecated
+        stuff = data[0].split('-')
+        if len(stuff) == 3:
+            data = stuff + data[1:]
+    if len(data) == 4:
+        s = data[3]
+        i = s.find('+')
+        if i == -1:
+            i = s.find('-')
+        if i > 0:
+            data[3:] = [s[:i], s[i:]]
+        else:
+            data.append('') # Dummy tz
+    if len(data) < 5:
+        return None
+    data = data[:5]
+    [dd, mm, yy, tm, tz] = data
+    mm = mm.lower()
+    if mm not in _monthnames:
+        dd, mm = mm, dd.lower()
+        if mm not in _monthnames:
+            return None
+    mm = _monthnames.index(mm) + 1
+    if mm > 12:
+        mm -= 12
+    if dd[-1] == ',':
+        dd = dd[:-1]
+    i = yy.find(':')
+    if i > 0:
+        yy, tm = tm, yy
+    if yy[-1] == ',':
+        yy = yy[:-1]
+    if not yy[0].isdigit():
+        yy, tz = tz, yy
+    if tm[-1] == ',':
+        tm = tm[:-1]
+    tm = tm.split(':')
+    if len(tm) == 2:
+        [thh, tmm] = tm
+        tss = '0'
+    elif len(tm) == 3:
+        [thh, tmm, tss] = tm
+    elif len(tm) == 1 and '.' in tm[0]:
+        # Some non-compliant MUAs use '.' to separate time elements.
+        tm = tm[0].split('.')
+        if len(tm) == 2:
+            [thh, tmm] = tm
+            tss = 0
+        elif len(tm) == 3:
+            [thh, tmm, tss] = tm
+    else:
+        return None
+    try:
+        yy = int(yy)
+        dd = int(dd)
+        thh = int(thh)
+        tmm = int(tmm)
+        tss = int(tss)
+    except ValueError:
+        return None
+    # Check for a yy specified in two-digit format, then convert it to the
+    # appropriate four-digit format, according to the POSIX standard. RFC 822
+    # calls for a two-digit yy, but RFC 2822 (which obsoletes RFC 822)
+    # mandates a 4-digit yy. For more information, see the documentation for
+    # the time module.
+    if yy < 100:
+        # The year is between 1969 and 1999 (inclusive).
+        if yy > 68:
+            yy += 1900
+        # The year is between 2000 and 2068 (inclusive).
+        else:
+            yy += 2000
+    tzoffset = None
+    tz = tz.upper()
+    if tz in _timezones:
+        tzoffset = _timezones[tz]
+    else:
+        try:
+            tzoffset = int(tz)
+        except ValueError:
+            pass
+        if tzoffset==0 and tz.startswith('-'):
+            tzoffset = None
+    # Convert a timezone offset into seconds ; -0500 -> -18000
+    if tzoffset:
+        if tzoffset < 0:
+            tzsign = -1
+            tzoffset = -tzoffset
+        else:
+            tzsign = 1
+        tzoffset = tzsign * ( (tzoffset//100)*3600 + (tzoffset % 100)*60)
+    # Daylight Saving Time flag is set to -1, since DST is unknown.
+    return [yy, mm, dd, thh, tmm, tss, 0, 1, -1, tzoffset]
+
+
+def parsedate_to_datetime(data):
+    dtuple, tz = _parsedate_tz(data)
+    if tz is None:
+        return datetime.datetime(*dtuple[:6])
+    return datetime.datetime(
+        *dtuple[:6],
+        tzinfo=datetime.timezone(datetime.timedelta(seconds=tz)))