gh-NNNNNN: Add property tests for strftime/strptime

Lib/test/test_datetime_property.py

@@ -0,0 +1,291 @@
+import datetime
+import unittest
+from test.support.hypothesis_helper import hypothesis
+
+st = hypothesis.strategies
+
+
+class FormatSet:
+    def __init__(self, children, must_use=False):
+        if children is None:
+            self.children = ()
+        else:
+            if must_use:
+                self.children = tuple(children)
+            else:
+                self.children = (*children, NoComponent)
+
+    def __repr__(self):
+        import textwrap
+
+        children = textwrap.indent(str(self.children), prefix="    ")
+        return f"{self.__class__.__name__}(\n{children}\n)"
+
+    def replace_children(self, children):
+        return type(self)(children, must_use=True)
+
+
+class OneFormatFrom(FormatSet):
+    pass
+
+
+class EachFormatFrom(FormatSet):
+    pass
+
+
+class NoComponentClass:
+    def __repr__(self):
+        return "NoComponent()"
+
+
+NoComponent = NoComponentClass()
+
+# Composite dates
+DATE_FORMAT_CODES = OneFormatFrom(
+    (
+        EachFormatFrom(
+            (
+                EachFormatFrom(
+                    (
+                        OneFormatFrom(("%Y", "%y")),
+                        OneFormatFrom(
+                            (
+                                # Month and Day
+                                EachFormatFrom(
+                                    (
+                                        OneFormatFrom(("%m", "%B", "%b")),
+                                        OneFormatFrom(("%d",)),
+                                    )
+                                ),
+                                # Julian day of year
+                                OneFormatFrom(("%j",)),
+                                # Week number and day of week (Sunday = 0)
+                                EachFormatFrom(
+                                    (
+                                        OneFormatFrom(("%W",)),
+                                        OneFormatFrom(("%w",)),
+                                    ),
+                                ),
+                                # Week number and day of week (Monday = 0)
+                                EachFormatFrom(
+                                    (
+                                        OneFormatFrom(("%U",)),
+                                        OneFormatFrom(("%u",)),
+                                    ),
+                                ),
+                            ),
+                        ),
+                    ),
+                ),
+                OneFormatFrom(("%A", "%a")),
+            ),
+        ),
+        # Full spec
+        OneFormatFrom(("%x",)),
+        # ISO 8601
+        EachFormatFrom(
+            (
+                OneFormatFrom(("%G",), must_use=True),
+                OneFormatFrom(("%V",), must_use=True),
+                OneFormatFrom(("%u", "%a", "%A"), must_use=True),
+            )
+        ),
+    )
+)
+
+
+TIME_FORMAT_CODES = EachFormatFrom(
+    (
+        OneFormatFrom(
+            (
+                EachFormatFrom(
+                    (
+                        OneFormatFrom(("%H", "%I")),
+                        OneFormatFrom(("%p",)),
+                        OneFormatFrom(("%M",)),
+                        OneFormatFrom(("%S",)),
+                        OneFormatFrom(("%f",)),
+                    )
+                ),
+                OneFormatFrom(("%X",), must_use=True),
+            )
+        ),
+        EachFormatFrom(
+            (
+                OneFormatFrom(("%z", "%:z")),
+                OneFormatFrom(("%Z",)),
+            ),
+        ),
+    )
+)
+
+DATETIME_FORMAT_CODES = OneFormatFrom(
+    (
+        EachFormatFrom(
+            (
+                DATE_FORMAT_CODES,
+                TIME_FORMAT_CODES,
+            ),
+        ),
+        OneFormatFrom(("%c",)),
+    ),
+)
+
+
+class DatetimeFormat:
+    def __init__(self, format_codes, format_str):
+        self.codes = format_codes
+        self.fmt = format_str
+
+    def __repr__(self):
+        return f"{self.__class__.__name__}(format_codes={self.codes}, format_str={self.fmt})"
+
+    def __bool__(self):
+        return bool(self.fmt)
+
+
+def _make_strftime_strategy(format_codes, exclude=frozenset()):
+    """Generates a strategy that generates valid strftime strings."""
+
+    def _exclude_codes(code_set):
+        new_children = []
+        for child in code_set.children:
+            if child is NoComponent:
+                new_children.append(child)
+            elif isinstance(child, str):
+                if child in exclude:
+                    continue
+                new_children.append(child)
+            else:
+                new_sub_node = _exclude_codes(child)
+                if new_sub_node is None:
+                    continue
+                new_children.append(_exclude_codes(child))
+
+        if (
+            not new_children
+            or len(new_children) == 1
+            and new_children[0] is NoComponent
+        ):
+            return None
+
+        return code_set.replace_children(children=new_children)
+
+    def select_formats(draw, code_set):
+        stack = [code_set]
+        output = []
+        while stack:
+            node = stack.pop()
+            if node is NoComponent:
+                continue
+
+            if isinstance(node, str):
+                output.append(node)
+            elif isinstance(node, EachFormatFrom):
+                for child in node.children:
+                    stack.append(child)
+            elif isinstance(node, OneFormatFrom):
+                stack.append(draw(st.sampled_from(node.children)))
+            else:
+                raise TypeError(f"Unknown node type: {type(node)}")
+
+        return output
+
+    format_codes = _exclude_codes(format_codes)
+
+    @st.composite
+    def _strftime_strategy(draw):
+        # Randomly select one format code from each date component category
+        selected_formats = select_formats(draw, format_codes)
+
+        # Choose a random order
+        selected_formats = draw(st.permutations(selected_formats))
+
+        # Add interstitial components
+        components = []
+
+        def _make_interstitial():
+            if draw(st.booleans()):
+                interstitial_text = draw(st.text()).replace("%", "%%")
+            else:
+                interstitial_text = ""
+            return interstitial_text
+
+        for component in selected_formats:
+            components.append(_make_interstitial())
+            components.append(component)
+        components.append(_make_interstitial())
+
+        format_str = "".join(components)
+        return DatetimeFormat(
+            format_codes=frozenset(selected_formats), format_str=format_str
+        )
+
+    return _strftime_strategy
+
+
+def datetime_strftimes(*args, **kwargs):
+    return _make_strftime_strategy(DATETIME_FORMAT_CODES, *args, **kwargs)()
+
+
+all_timezones = st.one_of(
+    st.timezones(),
+    st.none(),
+    st.tuples(
+        st.timedeltas(
+            min_value=-datetime.timedelta(hours=24),
+            max_value=datetime.timedelta(hours=24),
+        ),
+        st.one_of(st.none(), st.text()),
+    ).map(lambda x: datetime.timezone(*x)),
+)
+
+
+class DateTimeTest(unittest.TestCase):
+    theclass = datetime.datetime
+
+    @hypothesis.given(
+        dt=st.datetimes(timezones=st.timezones()),
+        # gh-12137: strptime does not accept "%:z"
+        fmt=datetime_strftimes(exclude={"%:z"}).filter(lambda x: x),
+    )
+    def test_strftime_strptime_property(self, dt, fmt):
+        fmt_code = fmt.fmt
+        # gh-124531: \x00 terminates format strings
+        hypothesis.assume("\x00" not in fmt_code)
+
+        # This first step can be lossy so without more extensive logic, we
+        # cannot directly make assertions about what this does.
+        dt_str = dt.strftime(fmt_code)
+
+        # gh-124529: %c does not work for years < 1000
+        hypothesis.assume(not ("%c" in fmt.codes and dt.year < 1000))
+
+        # gh-66571: These can only be parsed back in specific situations
+        hypothesis.assume(not "%Z" in fmt.codes)
+
+        # From here on out strptime/strftime rounds should be idempotent
+        dt_rt = self.theclass.strptime(dt_str, fmt_code)
+
+        dt_rt_str = dt_rt.strftime(fmt_code)
+        if (
+            (
+                not ({"%a", "%A", "%w", "%u"} & fmt.codes)
+                or (
+                    ("%Y" in fmt.codes or "%y" in fmt.codes)
+                    and ("%j" in fmt.codes or ("%m" in fmt.codes and "%b" in fmt.codes))
+                )
+                or ("%G" in fmt.codes)
+            )
+            and not ("%p" in fmt.codes and not ({"%H", "%I"} & fmt.codes))
+            and not any(
+                x in fmt_code
+                for x in ("%z%j", "%z%H", "%z%I", "%z%f", "%z%d", "%z%m", "%z%S")
+            )
+        ):
+            self.assertEqual(dt_rt_str, dt_str)
+
+        # Normally we would need to worry about whether or not one of these
+        # is ambiguous, but strptime can only generate code with fixed offsets.
+        dt_rt_2 = self.theclass.strptime(dt_rt_str, fmt_code)
+        self.assertEqual(dt_rt_2, dt_rt)