parametrized: ids: support generator/iterator

Fixes #759

- Adjust test_parametrized_ids_invalid_type, create list to convert tuples
  Ref: #1857 (comment)

- Changelog for int to str conversion
  Ref: #1857 (comment)

changelog/1857.improvement.rst

@@ -0,0 +1 @@
+``pytest.mark.parametrize`` accepts integers for ``ids`` again, converting it to strings.

changelog/759.improvement.rst

@@ -0,0 +1 @@
+``pytest.mark.parametrize`` supports iterators and generators for ``ids``.

src/_pytest/python.py

@@ -952,13 +952,21 @@ def parametrize(self, argnames, argvalues, indirect=False, ids=None, scope=None)
             function so that it can perform more expensive setups during the
             setup phase of a test rather than at collection time.
 
-        :arg ids: list of string ids, or a callable.
-            If strings, each is corresponding to the argvalues so that they are
-            part of the test id. If None is given as id of specific test, the
-            automatically generated id for that argument will be used.
-            If callable, it should take one argument (a single argvalue) and return
-            a string or return None. If None, the automatically generated id for that
-            argument will be used.
+        :arg ids: sequence of (or generator for) ids for ``argvalues``,
+              or a callable to return part of the id for each argvalue.
+
+            With sequences (and generators like ``itertools.count()``) the
+            returned ids should be of type ``string``, ``int``, ``float``,
+            ``bool``, or ``None``.
+            They are mapped to the corresponding index in ``argvalues``.
+            ``None`` means to use the auto-generated id.
+
+            If it is a callable it will be called for each entry in
+            ``argvalues``, and the return value is used as part of the
+            auto-generated id for the whole set.
+            This is useful to provide more specific ids for certain items, e.g.
+            dates.  Returning ``None`` will use an auto-generated id.
+
             If no ids are provided they will be generated automatically from
             the argvalues.
 
@@ -1028,26 +1036,47 @@ def _resolve_arg_ids(self, argnames, ids, parameters, item):
         :rtype: List[str]
         :return: the list of ids for each argname given
         """
-        from _pytest._io.saferepr import saferepr
-
         idfn = None
         if callable(ids):
             idfn = ids
             ids = None
         if ids:
             func_name = self.function.__name__
-            if len(ids) != len(parameters):
-                msg = "In {}: {} parameter sets specified, with different number of ids: {}"
-                fail(msg.format(func_name, len(parameters), len(ids)), pytrace=False)
-            for id_value in ids:
-                if id_value is not None and not isinstance(id_value, str):
-                    msg = "In {}: ids must be list of strings, found: {} (type: {!r})"
+            ids = self._validate_ids(ids, parameters, func_name)
+        ids = idmaker(argnames, parameters, idfn, ids, self.config, item=item)
+        return ids
+
+    def _validate_ids(self, ids, parameters, func_name):
+        try:
+            len(ids)
+        except TypeError:
+            try:
+                it = iter(ids)
+            except TypeError:
+                raise TypeError("ids must be a callable, sequence or generator")
+            else:
+                import itertools
+
+                new_ids = list(itertools.islice(it, len(parameters)))
+        else:
+            new_ids = list(ids)
+
+        if len(new_ids) != len(parameters):
+            msg = "In {}: {} parameter sets specified, with different number of ids: {}"
+            fail(msg.format(func_name, len(parameters), len(ids)), pytrace=False)
+        for idx, id_value in enumerate(new_ids):
+            if id_value is not None:
+                if isinstance(id_value, (float, int, bool)):
+                    new_ids[idx] = str(id_value)
+                elif not isinstance(id_value, str):
+                    from _pytest._io.saferepr import saferepr
+
+                    msg = "In {}: ids must be list of string/float/int/bool, found: {} (type: {!r}) at index {}"
                     fail(
-                        msg.format(func_name, saferepr(id_value), type(id_value)),
+                        msg.format(func_name, saferepr(id_value), type(id_value), idx),
                         pytrace=False,
                     )
-        ids = idmaker(argnames, parameters, idfn, ids, self.config, item=item)
-        return ids
+        return new_ids
 
     def _resolve_arg_value_types(self, argnames, indirect):
         """Resolves if each parametrized argument must be considered a parameter to a fixture or a "funcarg"

testing/python/metafunc.py

@@ -9,6 +9,7 @@
 import pytest
 from _pytest import fixtures
 from _pytest import python
+from _pytest.outcomes import fail
 
 
 class TestMetafunc:
@@ -61,6 +62,39 @@ def func(x, y):
         pytest.raises(ValueError, lambda: metafunc.parametrize("y", [5, 6]))
         pytest.raises(ValueError, lambda: metafunc.parametrize("y", [5, 6]))
 
+        with pytest.raises(
+            TypeError, match="^ids must be a callable, sequence or generator$"
+        ):
+            metafunc.parametrize("y", [5, 6], ids=42)
+
+    def test_parametrize_error_iterator(self):
+        def func(x):
+            raise NotImplementedError()
+
+        class Exc(Exception):
+            def __repr__(self):
+                return "Exc(from_gen)"
+
+        def gen():
+            yield 0
+            yield None
+            yield Exc()
+
+        metafunc = self.Metafunc(func)
+        metafunc.parametrize("x", [1, 2], ids=gen())
+        assert [(x.funcargs, x.id) for x in metafunc._calls] == [
+            ({"x": 1}, "0"),
+            ({"x": 2}, "2"),
+        ]
+        with pytest.raises(
+            fail.Exception,
+            match=(
+                r"In func: ids must be list of string/float/int/bool, found:"
+                r" Exc\(from_gen\) \(type: <class .*Exc'>\) at index 2"
+            ),
+        ):
+            metafunc.parametrize("x", [1, 2, 3], ids=gen())
+
     def test_parametrize_bad_scope(self, testdir):
         def func(x):
             pass
@@ -534,9 +568,22 @@ def ids(d):
             @pytest.mark.parametrize("arg", ({1: 2}, {3, 4}), ids=ids)
             def test(arg):
                 assert arg
+
+            @pytest.mark.parametrize("arg", (1, 2.0, True), ids=ids)
+            def test_int(arg):
+                assert arg
             """
         )
-        assert testdir.runpytest().ret == 0
+        result = testdir.runpytest("-vv", "-s")
+        result.stdout.fnmatch_lines(
+            [
+                "test_parametrize_ids_returns_non_string.py::test[arg0] PASSED",
+                "test_parametrize_ids_returns_non_string.py::test[arg1] PASSED",
+                "test_parametrize_ids_returns_non_string.py::test_int[1] PASSED",
+                "test_parametrize_ids_returns_non_string.py::test_int[2.0] PASSED",
+                "test_parametrize_ids_returns_non_string.py::test_int[True] PASSED",
+            ]
+        )
 
     def test_idmaker_with_ids(self):
         from _pytest.python import idmaker
@@ -1186,20 +1233,21 @@ def test_temp(temp):
         result.stdout.fnmatch_lines(["* 1 skipped *"])
 
     def test_parametrized_ids_invalid_type(self, testdir):
-        """Tests parametrized with ids as non-strings (#1857)."""
+        """Test error with non-strings/non-ints, without generator (#1857)."""
         testdir.makepyfile(
             """
             import pytest
 
-            @pytest.mark.parametrize("x, expected", [(10, 20), (40, 80)], ids=(None, 2))
+            @pytest.mark.parametrize("x, expected", [(1, 2), (3, 4), (5, 6)], ids=(None, 2, type))
             def test_ids_numbers(x,expected):
                 assert x * 2 == expected
         """
         )
         result = testdir.runpytest()
         result.stdout.fnmatch_lines(
             [
-                "*In test_ids_numbers: ids must be list of strings, found: 2 (type: *'int'>)*"
+                "In test_ids_numbers: ids must be list of string/float/int/bool,"
+                " found: <class 'type'> (type: <class 'type'>) at index 2"
             ]
         )
 
@@ -1776,3 +1824,39 @@ def test_foo(a):
         )
         result = testdir.runpytest()
         result.assert_outcomes(passed=1)
+
+    def test_parametrize_iterator(self, testdir):
+        testdir.makepyfile(
+            """
+            import itertools
+            import pytest
+
+            id_parametrize = pytest.mark.parametrize(
+                ids=("param%d" % i for i in itertools.count())
+            )
+
+            @id_parametrize('y', ['a', 'b'])
+            def test1(y):
+                pass
+
+            @id_parametrize('y', ['a', 'b'])
+            def test2(y):
+                pass
+
+            @pytest.mark.parametrize("a, b", [(1, 2), (3, 4)], ids=itertools.count())
+            def test_converted_to_str(a, b):
+                pass
+        """
+        )
+        result = testdir.runpytest("-vv", "-s")
+        result.stdout.fnmatch_lines_random(  # random for py35.
+            [
+                "test_parametrize_iterator.py::test1[param0] PASSED",
+                "test_parametrize_iterator.py::test1[param1] PASSED",
+                "test_parametrize_iterator.py::test2[param2] PASSED",
+                "test_parametrize_iterator.py::test2[param3] PASSED",
+                "test_parametrize_iterator.py::test_converted_to_str[0] PASSED",
+                "test_parametrize_iterator.py::test_converted_to_str[1] PASSED",
+                "*= 6 passed in *",
+            ]
+        )