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"""
This module defines a Duration class.
The class Duration allows to define durations in years and months and can be
used as limited replacement for timedelta objects.
"""
from datetime import timedelta
from decimal import Decimal, ROUND_FLOOR
def fquotmod(val, low, high):
"""
A divmod function with boundaries.
"""
# assumes that all the maths is done with Decimals.
# divmod for Decimal uses truncate instead of floor as builtin
# divmod, so we have to do it manually here.
a, b = val - low, high - low
div = (a / b).to_integral(ROUND_FLOOR)
mod = a - div * b
# if we were not usig Decimal, it would look like this.
# 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.
"""
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:
"""
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.
The algorithm to add a duration to a date is defined at
http://www.w3.org/TR/xmlschema-2/#adding-durations-to-dateTimes
"""
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.
"""
if not isinstance(months, Decimal):
months = Decimal(str(months))
if not isinstance(years, Decimal):
years = Decimal(str(years))
self.months = months
self.years = years
self.tdelta = timedelta(
days, seconds, microseconds, milliseconds, minutes, hours, weeks
)
def __getstate__(self):
return self.__dict__
def __setstate__(self, state):
self.__dict__.update(state)
def __getattr__(self, name):
"""
Provide direct access to attributes of included timedelta instance.
"""
return getattr(self.tdelta, name)
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:
fmt = "%d months"
if self.months <= 1:
fmt = "%d month"
params.append(fmt % 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 __hash__(self):
"""
Return a hash of this instance so that it can be used in, for
example, dicts and sets.
"""
return hash((self.tdelta, self.months, self.years))
def __neg__(self):
"""
A simple unary minus.
Returns a new Duration instance with all it's negated.
"""
negduration = Duration(years=-self.years, months=-self.months)
negduration.tdelta = -self.tdelta
return negduration
def __add__(self, other):
"""
Durations can be added with Duration, timedelta, date and datetime
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
try:
# try anything that looks like a date or datetime
# 'other' has attributes year, month, day
# and relies on 'timedelta + other' being implemented
if not (float(self.years).is_integer() and float(self.months).is_integer()):
raise ValueError(
"fractional years or months not supported" " for date calculations"
)
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=int(newyear), month=int(newmonth), day=int(newday)
)
# does a timedelta + date/datetime
return self.tdelta + newdt
except AttributeError:
# other probably was not a date/datetime compatible object
pass
try:
# try if other is a timedelta
# relies on timedelta + timedelta supported
newduration = Duration(years=self.years, months=self.months)
newduration.tdelta = self.tdelta + other
return newduration
except AttributeError:
# ignore ... other probably was not a timedelta compatible object
pass
# we have tried everything .... return a NotImplemented
return NotImplemented
__radd__ = __add__
def __mul__(self, other):
if isinstance(other, int):
newduration = Duration(years=self.years * other, months=self.months * other)
newduration.tdelta = self.tdelta * other
return newduration
return NotImplemented
__rmul__ = __mul__
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
try:
# do maths with our timedelta object ....
newduration = Duration(years=self.years, months=self.months)
newduration.tdelta = self.tdelta - other
return newduration
except TypeError:
# looks like timedelta - other is not implemented
pass
return NotImplemented
def __rsub__(self, other):
"""
It is possible to subtract Duration objecs from date, datetime and
timedelta objects.
TODO: there is some weird behaviour in date - timedelta ...
if timedelta has seconds or microseconds set, then
date - timedelta != date + (-timedelta)
for now we follow this behaviour to avoid surprises when mixing
timedeltas with Durations, but in case this ever changes in
the stdlib we can just do:
return -self + other
instead of all the current code
"""
if isinstance(other, timedelta):
tmpdur = Duration()
tmpdur.tdelta = other
return tmpdur - self
try:
# check if other behaves like a date/datetime object
# does it have year, month, day and replace?
if not (float(self.years).is_integer() and float(self.months).is_integer()):
raise ValueError(
"fractional years or months not supported" " for date calculations"
)
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=int(newyear), month=int(newmonth), day=int(newday)
)
return newdt - self.tdelta
except AttributeError:
# other probably was not compatible with data/datetime
pass
return NotImplemented
def __eq__(self, other):
"""
If the years, month part and the timedelta part are both equal, then
the two Durations are considered equal.
"""
if isinstance(other, Duration):
if (self.years * 12 + self.months) == (
other.years * 12 + other.months
) and self.tdelta == other.tdelta:
return True
return False
# check if other con be compared against timedelta object
# will raise an AssertionError when optimisation is off
if self.years == 0 and self.months == 0:
return self.tdelta == other
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 isinstance(other, Duration):
if (self.years * 12 + self.months) != (
other.years * 12 + other.months
) or self.tdelta != other.tdelta:
return True
return False
# check if other can be compared against timedelta object
# will raise an AssertionError when optimisation is off
if self.years == 0 and self.months == 0:
return self.tdelta != other
return True
def totimedelta(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)
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