* added ISO 8601 formating methods

* still problems with negative durations
* refactored Duration class to separate module
* allow access to wrapped timedelta attributes directly on Duration.
* refactored tzinfo parsing and formating into separate module
* updated test cases for new functionality

1 files changed, 20 insertions, 205 deletions

diff --git a/src/isodate/isoduration.py b/src/isodate/isoduration.py
index ebbd7eb..5002e51 100644
--- a/src/isodate/isoduration.py
+++ b/src/isodate/isoduration.py
@@ -27,14 +27,16 @@
 '''
 This module provides an ISO 8601:2004 duration parser.
 
-It also defines a class Duration, which allows to define
-durations in years and months. 
+It also provides a wrapper to strftime. This wrapper makes it easier to
+format timedelta or Duration instances as ISO conforming strings.
 '''
-from datetime import date, datetime, timedelta
+from datetime import timedelta
 import re
 
+from isodate.duration import Duration
 from isodate.isoerror import ISO8601Error
 from isodate.isodatetime import parse_datetime
+from isodate.isostrf import strftime, D_DEFAULT
 
 ISO8601_PERIOD_REGEX = re.compile(r"^(?P<sign>[+-])?"
                 r"P(?P<years>[0-9]+([,.][0-9]+)?Y)?"
@@ -117,208 +119,21 @@ def parse_duration(datestring):
             ret = Duration(0) - ret
     return ret
 
-
-def fquotmod(val, low, high):
-    '''
-    A divmod function with boundaries.
-    '''
-    div, mod = divmod(val - low, high - low)
-    mod += low
-    return int(div), mod
-
-def max_days_in_month(year, month):
-    '''
-    Determines the number of days of a specific month in a specific year.
+def duration_isoformat(tduration, format=D_DEFAULT):
     '''
-    if month in (1, 3, 5, 7, 8, 10, 12):
-        return 31
-    if month in (4, 6, 9, 11):
-        return 30
-    if ((year % 400) == 0) or ((year % 100) != 0) and ((year % 4) == 0):
-        return 29
-    return 28
-
-class Duration(object):
-    '''
-    A class which represents a duration. 
-    
-    The difference to datetime.timedelta is, that this class handles also
-    differences given in years and months.
-    A Duration treats differences given in year, months separately from all
-    other components. 
-    
-    A Duration can be used almost like any timedelta object, however there
-    are some restrictions:
-      * It is not really possible to compare Durations, because it is unclear,
-        whether a duration of 1 year is bigger than 365 days or not.
-      * Equality is only tested between the two (year, month vs. timedelta)
-        basic components.
-        
-    A Duration can also be converted into a datetime object, but this requires
-    a start date or an end date.
+    Format duration strings. 
     
-    The algorithm to add a duration to a date is defined at
-    http://www.w3.org/TR/xmlschema-2/#adding-durations-to-dateTimes
+    This method is just a wrapper around isodate.isostrf.strftime and uses
+    P%P (D_DEFAULT) as default format.
     '''
-    
-    def __init__(self, days=0, seconds=0, microseconds=0, milliseconds=0,
-                 minutes=0, hours=0, weeks=0, months=0, years=0):
-        '''
-        Initialise this Duration instance with the given parameters.
-        '''
-        self.months = months
-        self.years = years
-        self.tdelta = timedelta(days, seconds, microseconds, milliseconds,
-                                minutes, hours, weeks)
-
-    def __str__(self):
-        '''
-        Return a string representation of this duration similar to timedelta.
-        '''
-        params = []
-        if self.years:
-            params.append('%d years' % self.years)
-        if self.months:
-            params.append('%d months' % self.months)
-        params.append(str(self.tdelta))
-        return ', '.join(params)
-    
-    def __repr__(self):
-        '''
-        Return a string suitable for repr(x) calls.
-        '''
-        return "%s.%s(%d, %d, %d, years=%d, months=%d)" % (
-                self.__class__.__module__, self.__class__.__name__, 
-                self.tdelta.days, self.tdelta.seconds, 
-                self.tdelta.microseconds, self.years, self.months)
-
-    def __add__(self, other):
-        '''
-        Durations can be added with Duration, timedelta, date and datetime
-        objects.
-        '''
-        if isinstance(other, timedelta):
-            newduration = Duration(years=self.years, months=self.months)
-            newduration.tdelta = self.tdelta + other
-            return newduration
-        if isinstance(other, Duration):
-            newduration = Duration(years=self.years+other.years, 
-                                   months=self.months+other.months)
-            newduration.tdelta = self.tdelta + other.tdelta
-            return newduration
-        if isinstance(other, (date, datetime)):
-            newmonth = other.month + self.months
-            carry, newmonth = fquotmod(newmonth, 1, 13)
-            newyear = other.year + self.years + carry
-            maxdays = max_days_in_month(newyear, newmonth)
-            if other.day > maxdays:
-                newday = maxdays
-            else:
-                newday = other.day
-            newdt = other.replace(year=newyear, month=newmonth, day=newday)
-            return self.tdelta + newdt
-        raise TypeError('unsupported operand type(s) for +: %s and %s' % 
-                        (self.__class__, other.__class__))
-        
-        
-    def __radd__(self, other):
-        '''
-        Add durations to timedelta, date and datetime objects.
-        '''
-        if isinstance(other, timedelta):
-            newduration = Duration(years=self.years, months=self.months)
-            newduration.tdelta = self.tdelta + other
-            return newduration
-        if isinstance(other, (date, datetime)):
-            newmonth = other.month + self.months
-            carry, newmonth = fquotmod(newmonth, 1, 13)
-            newyear = other.year + self.years + carry
-            maxdays = max_days_in_month(newyear, newmonth)
-            if other.day > maxdays:
-                newday = maxdays
-            else:
-                newday = other.day
-            newdt = other.replace(year=newyear, month=newmonth, day=newday)
-            return newdt + self.tdelta
-        raise TypeError('unsupported operand type(s) for +: %s and %s' % 
-                        (other.__class__, self.__class__))
-    
-    def __sub__(self, other):
-        '''
-        It is possible to subtract Duration and timedelta objects from Duration
-        objects.
-        '''
-        if isinstance(other, Duration):
-            newduration = Duration(years=self.years-other.years, 
-                                   months=self.months-other.months)
-            newduration.tdelta = self.tdelta - other.tdelta
-            return newduration
-        if isinstance(other, timedelta):
-            newduration = Duration(years=self.years, months=self.months)
-            newduration.tdelta = self.tdelta - other
-            return newduration
-        raise TypeError('unsupported operand type(s) for -: %s and %s' % 
-                        (self.__class__, other.__class__))
-        
-    def __rsub__(self, other):
-        '''
-        It is possible to subtract Duration objecs from date, datetime and 
-        timedelta objects.
-        '''
-        #print '__rsub__:', self, other
-        if isinstance(other, (date, datetime)):
-            newmonth = other.month - self.months
-            carry, newmonth = fquotmod(newmonth, 1, 13)
-            newyear = other.year - self.years + carry
-            maxdays = max_days_in_month(newyear, newmonth)
-            if other.day > maxdays:
-                newday = maxdays
-            else:
-                newday = other.day
-            newdt = other.replace(year=newyear, month=newmonth, day=newday)
-            return newdt - self.tdelta
-        if isinstance(other, timedelta):
-            tmpdur = Duration()
-            tmpdur.tdelta = other
-            return tmpdur - self
-        raise TypeError('unsupported operand type(s) for -: %s and %s' % 
-                        (other.__class__, self.__class__))
-    
-    def __eq__(self, other):
-        '''
-        If the years, month part and the timedelta part are both equal, then
-        the two Durations are considered equal.
-        '''
-        if not isinstance(other, Duration):
-            return NotImplemented
-        if ((self.years * 12 + self.months) == 
-            (other.years * 12 + other.months) and self.tdelta == other.tdelta):
-            return True
-        return False
-    
-    def __ne__(self, other):
-        '''
-        If the years, month part or the timedelta part is not equal, then
-        the two Durations are considered not equal.
-        '''
-        if not isinstance(other, Duration):
-            return NotImplemented
-        if ((self.years * 12 + self.months) != 
-            (other.years * 12 + other.months) or self.tdelta != other.tdelta):
-            return True
-        return False
-    
-    def todatetime(self, start=None, end=None):
-        '''
-        Convert this duration into a timedelta object.
-        
-        This method requires a start datetime or end datetimem, but raises
-        an exception if both are given.
-        '''
-        if start is None and end is None:
-            raise ValueError("start or end required")
-        if start is not None and end is not None:
-            raise ValueError("only start or end allowed")
-        if start is not None:
-            return (start + self) - start
-        return end - (end - self)
+    # TODO: implement better decision for negative Durations.
+    #       should be done in Duration class in consistent way with timedelta.
+    if ((isinstance(tduration, Duration) and (tduration.years < 0 or 
+                                             tduration.months < 0 or
+                                             tduration.tdelta < timedelta(0)))
+        or (isinstance(tduration, timedelta) and (tduration < timedelta(0)))):
+        ret = '-'
+    else:
+        ret = ''
+    ret += strftime(tduration, format)
+    return ret