Calculate number of days

Some months have fewer than 31 days!  Shocking but true.

hypothesis-python/RELEASE.rst

@@ -0,0 +1,4 @@
+RELEASE_TYPE: patch
+
+This patch makes :func:`~hypothesis.strategies.datetimes` more efficient,
+as it now handles short months correctly by construction instead of filtering.

hypothesis-python/src/hypothesis/searchstrategy/datetime.py

@@ -18,6 +18,7 @@
 from __future__ import absolute_import, division, print_function
 
 import datetime as dt
+from calendar import monthrange
 
 from hypothesis.internal.conjecture import utils
 from hypothesis.searchstrategy.strategies import SearchStrategy
@@ -44,39 +45,32 @@ def __init__(self, min_value, max_value, timezones_strat):
         self.max_dt = max_value
         self.tz_strat = timezones_strat
 
-    def _attempt_one_draw(self, data):
+    def do_draw(self, data):
         result = dict()
         cap_low, cap_high = True, True
         for name in ("year", "month", "day", "hour", "minute", "second", "microsecond"):
             low = getattr(self.min_dt if cap_low else dt.datetime.min, name)
             high = getattr(self.max_dt if cap_high else dt.datetime.max, name)
+            if name == "day" and not cap_high:
+                _, high = monthrange(**result)
             if name == "year":
                 val = utils.integer_range(data, low, high, 2000)
             else:
                 val = utils.integer_range(data, low, high)
             result[name] = val
             cap_low = cap_low and val == low
             cap_high = cap_high and val == high
+        result = dt.datetime(**result)
         tz = data.draw(self.tz_strat)
         try:
-            result = dt.datetime(**result)
             if is_pytz_timezone(tz):
                 # Can't just construct; see http://pytz.sourceforge.net
                 return tz.normalize(tz.localize(result))
             return result.replace(tzinfo=tz)
         except (ValueError, OverflowError):
-            return None
-
-    def do_draw(self, data):
-        for _ in range(3):
-            result = self._attempt_one_draw(data)
-            if result is not None:
-                return result
-        data.note_event(
-            "3 attempts to create a datetime between %r and %r "
-            "with timezone from %r failed." % (self.min_dt, self.max_dt, self.tz_strat)
-        )
-        data.mark_invalid()
+            msg = "Failed to draw a datetime between %r and %r with timezone from %r."
+            data.note_event(msg % (self.min_dt, self.max_dt, self.tz_strat))
+            data.mark_invalid()
 
 
 class DateStrategy(SearchStrategy):

hypothesis-python/tests/cover/test_datetimes.py

@@ -23,9 +23,7 @@
 
 from hypothesis import given
 from hypothesis.internal.compat import hrange
-from hypothesis.internal.conjecture.data import ConjectureData, Status, StopTest
-from hypothesis.searchstrategy.datetime import DatetimeStrategy
-from hypothesis.strategies import binary, dates, datetimes, none, timedeltas, times
+from hypothesis.strategies import dates, datetimes, timedeltas, times
 from tests.common.debug import find_any, minimal
 
 
@@ -88,21 +86,6 @@ def test_bordering_on_a_leap_year():
     assert x.year == 2004
 
 
-def test_DatetimeStrategy_draw_may_fail():
-    def is_failure_inducing(b):
-        try:
-            return strat._attempt_one_draw(ConjectureData.for_buffer(b)) is None
-        except StopTest:
-            return False
-
-    strat = DatetimeStrategy(dt.datetime.min, dt.datetime.max, none())
-    failure_inducing = minimal(binary(), is_failure_inducing, timeout_after=30)
-    data = ConjectureData.for_buffer(failure_inducing * 100)
-    with pytest.raises(StopTest):
-        data.draw(strat)
-    assert data.status == Status.INVALID
-
-
 def test_can_find_after_the_year_2000():
     assert minimal(dates(), lambda x: x.year > 2000).year == 2001
 
@@ -111,9 +94,9 @@ def test_can_find_before_the_year_2000():
     assert minimal(dates(), lambda x: x.year < 2000).year == 1999
 
 
-def test_can_find_each_month():
-    for month in hrange(1, 13):
-        find_any(dates(), lambda x: x.month == month)
+@pytest.mark.parametrize("month", hrange(1, 13))
+def test_can_find_each_month(month):
+    find_any(dates(), lambda x: x.month == month)
 
 
 def test_min_year_is_respected():