Issue #18874: Implement the PEP 454 (tracemalloc)

6 files changed, 1285 insertions, 5 deletions

diff --git a/Lib/test/support/__init__.py b/Lib/test/support/__init__.py
index 87c039a..a242a47 100644
--- a/Lib/test/support/__init__.py
+++ b/Lib/test/support/__init__.py
@@ -2154,3 +2154,22 @@ def patch(test_instance, object_to_patch, attr_name, new_value):
 
     # actually override the attribute
     setattr(object_to_patch, attr_name, new_value)
+
+
+def run_in_subinterp(code):
+    """
+    Run code in a subinterpreter. Raise unittest.SkipTest if the tracemalloc
+    module is enabled.
+    """
+    # Issue #10915, #15751: PyGILState_*() functions don't work with
+    # sub-interpreters, the tracemalloc module uses these functions internally
+    try:
+        import tracemalloc
+    except ImportError:
+        pass
+    else:
+        if tracemalloc.is_tracing():
+            raise unittest.SkipTest("run_in_subinterp() cannot be used "
+                                     "if tracemalloc module is tracing "
+                                     "memory allocations")
+    return _testcapi.run_in_subinterp(code)
diff --git a/Lib/test/test_atexit.py b/Lib/test/test_atexit.py
index b641015..84644f1 100644
--- a/Lib/test/test_atexit.py
+++ b/Lib/test/test_atexit.py
@@ -158,7 +158,7 @@ class SubinterpreterTest(unittest.TestCase):
             atexit.register(f)
             del atexit
             """
-        ret = _testcapi.run_in_subinterp(code)
+        ret = support.run_in_subinterp(code)
         self.assertEqual(ret, 0)
         self.assertEqual(atexit._ncallbacks(), n)
 
@@ -173,7 +173,7 @@ class SubinterpreterTest(unittest.TestCase):
             atexit.register(f)
             atexit.__atexit = atexit
             """
-        ret = _testcapi.run_in_subinterp(code)
+        ret = support.run_in_subinterp(code)
         self.assertEqual(ret, 0)
         self.assertEqual(atexit._ncallbacks(), n)
 
diff --git a/Lib/test/test_capi.py b/Lib/test/test_capi.py
index d37c057..000079e 100644
--- a/Lib/test/test_capi.py
+++ b/Lib/test/test_capi.py
@@ -205,7 +205,7 @@ class SubinterpreterTest(unittest.TestCase):
                 pickle.dump(id(builtins), f)
             """.format(w)
         with open(r, "rb") as f:
-            ret = _testcapi.run_in_subinterp(code)
+            ret = support.run_in_subinterp(code)
             self.assertEqual(ret, 0)
             self.assertNotEqual(pickle.load(f), id(sys.modules))
             self.assertNotEqual(pickle.load(f), id(builtins))
diff --git a/Lib/test/test_threading.py b/Lib/test/test_threading.py
index 66eace0..a84577c 100644
--- a/Lib/test/test_threading.py
+++ b/Lib/test/test_threading.py
@@ -853,7 +853,7 @@ class SubinterpThreadingTests(BaseTestCase):
                 os.write(%d, b"x")
             threading.Thread(target=f).start()
             """ % (w,)
-        ret = _testcapi.run_in_subinterp(code)
+        ret = test.support.run_in_subinterp(code)
         self.assertEqual(ret, 0)
         # The thread was joined properly.
         self.assertEqual(os.read(r, 1), b"x")
@@ -885,7 +885,7 @@ class SubinterpThreadingTests(BaseTestCase):
                 os.write(%d, b"x")
             threading.Thread(target=f).start()
             """ % (w,)
-        ret = _testcapi.run_in_subinterp(code)
+        ret = test.support.run_in_subinterp(code)
         self.assertEqual(ret, 0)
         # The thread was joined properly.
         self.assertEqual(os.read(r, 1), b"x")
diff --git a/Lib/test/test_tracemalloc.py b/Lib/test/test_tracemalloc.py
new file mode 100644
index 0000000..ecb5aee
--- /dev/null
+++ b/Lib/test/test_tracemalloc.py
@@ -0,0 +1,797 @@
+import _tracemalloc
+import contextlib
+import datetime
+import os
+import sys
+import tracemalloc
+import unittest
+from unittest.mock import patch
+from test.script_helper import assert_python_ok, assert_python_failure
+from test import support
+try:
+    import threading
+except ImportError:
+    threading = None
+
+EMPTY_STRING_SIZE = sys.getsizeof(b'')
+
+def get_frames(nframe, lineno_delta):
+    frames = []
+    frame = sys._getframe(1)
+    for index in range(nframe):
+        code = frame.f_code
+        lineno = frame.f_lineno + lineno_delta
+        frames.append((code.co_filename, lineno))
+        lineno_delta = 0
+        frame = frame.f_back
+        if frame is None:
+            break
+    return tuple(frames)
+
+def allocate_bytes(size):
+    nframe = tracemalloc.get_traceback_limit()
+    bytes_len = (size - EMPTY_STRING_SIZE)
+    frames = get_frames(nframe, 1)
+    data = b'x' * bytes_len
+    return data, tracemalloc.Traceback(frames)
+
+def create_snapshots():
+    traceback_limit = 2
+
+    raw_traces = [
+        (10, (('a.py', 2), ('b.py', 4))),
+        (10, (('a.py', 2), ('b.py', 4))),
+        (10, (('a.py', 2), ('b.py', 4))),
+
+        (2, (('a.py', 5), ('b.py', 4))),
+
+        (66, (('b.py', 1),)),
+
+        (7, (('<unknown>', 0),)),
+    ]
+    snapshot = tracemalloc.Snapshot(raw_traces, traceback_limit)
+
+    raw_traces2 = [
+        (10, (('a.py', 2), ('b.py', 4))),
+        (10, (('a.py', 2), ('b.py', 4))),
+        (10, (('a.py', 2), ('b.py', 4))),
+
+        (2, (('a.py', 5), ('b.py', 4))),
+        (5000, (('a.py', 5), ('b.py', 4))),
+
+        (400, (('c.py', 578),)),
+    ]
+    snapshot2 = tracemalloc.Snapshot(raw_traces2, traceback_limit)
+
+    return (snapshot, snapshot2)
+
+def frame(filename, lineno):
+    return tracemalloc._Frame((filename, lineno))
+
+def traceback(*frames):
+    return tracemalloc.Traceback(frames)
+
+def traceback_lineno(filename, lineno):
+    return traceback((filename, lineno))
+
+def traceback_filename(filename):
+    return traceback_lineno(filename, 0)
+
+
+class TestTracemallocEnabled(unittest.TestCase):
+    def setUp(self):
+        if tracemalloc.is_tracing():
+            self.skipTest("tracemalloc must be stopped before the test")
+
+        tracemalloc.set_traceback_limit(1)
+        tracemalloc.start()
+
+    def tearDown(self):
+        tracemalloc.stop()
+
+    def test_get_tracemalloc_memory(self):
+        data = [allocate_bytes(123) for count in range(1000)]
+        size = tracemalloc.get_tracemalloc_memory()
+        self.assertGreaterEqual(size, 0)
+
+        tracemalloc.clear_traces()
+        size2 = tracemalloc.get_tracemalloc_memory()
+        self.assertGreaterEqual(size2, 0)
+        self.assertLessEqual(size2, size)
+
+    def test_get_object_traceback(self):
+        tracemalloc.clear_traces()
+        obj_size = 12345
+        obj, obj_traceback = allocate_bytes(obj_size)
+        traceback = tracemalloc.get_object_traceback(obj)
+        self.assertEqual(traceback, obj_traceback)
+
+    def test_set_traceback_limit(self):
+        obj_size = 10
+
+        nframe = tracemalloc.get_traceback_limit()
+        self.addCleanup(tracemalloc.set_traceback_limit, nframe)
+
+        self.assertRaises(ValueError, tracemalloc.set_traceback_limit, -1)
+
+        tracemalloc.clear_traces()
+        tracemalloc.set_traceback_limit(10)
+        obj2, obj2_traceback = allocate_bytes(obj_size)
+        traceback = tracemalloc.get_object_traceback(obj2)
+        self.assertEqual(len(traceback), 10)
+        self.assertEqual(traceback, obj2_traceback)
+
+        tracemalloc.clear_traces()
+        tracemalloc.set_traceback_limit(1)
+        obj, obj_traceback = allocate_bytes(obj_size)
+        traceback = tracemalloc.get_object_traceback(obj)
+        self.assertEqual(len(traceback), 1)
+        self.assertEqual(traceback, obj_traceback)
+
+
+    def find_trace(self, traces, traceback):
+        for trace in traces:
+            if trace[1] == traceback._frames:
+                return trace
+
+        self.fail("trace not found")
+
+    def test_get_traces(self):
+        tracemalloc.clear_traces()
+        obj_size = 12345
+        obj, obj_traceback = allocate_bytes(obj_size)
+
+        traces = tracemalloc._get_traces()
+        trace = self.find_trace(traces, obj_traceback)
+
+        self.assertIsInstance(trace, tuple)
+        size, traceback = trace
+        self.assertEqual(size, obj_size)
+        self.assertEqual(traceback, obj_traceback._frames)
+
+        tracemalloc.stop()
+        self.assertEqual(tracemalloc._get_traces(), [])
+
+
+    def test_get_traces_intern_traceback(self):
+        # dummy wrappers to get more useful and identical frames in the traceback
+        def allocate_bytes2(size):
+            return allocate_bytes(size)
+        def allocate_bytes3(size):
+            return allocate_bytes2(size)
+        def allocate_bytes4(size):
+            return allocate_bytes3(size)
+
+        # Ensure that two identical tracebacks are not duplicated
+        tracemalloc.clear_traces()
+        tracemalloc.set_traceback_limit(4)
+        obj_size = 123
+        obj1, obj1_traceback = allocate_bytes4(obj_size)
+        obj2, obj2_traceback = allocate_bytes4(obj_size)
+
+        traces = tracemalloc._get_traces()
+
+        trace1 = self.find_trace(traces, obj1_traceback)
+        trace2 = self.find_trace(traces, obj2_traceback)
+        size1, traceback1 = trace1
+        size2, traceback2 = trace2
+        self.assertEqual(traceback2, traceback1)
+        self.assertIs(traceback2, traceback1)
+
+    def test_get_traced_memory(self):
+        # Python allocates some internals objects, so the test must tolerate
+        # a small difference between the expected size and the real usage
+        max_error = 2048
+
+        # allocate one object
+        obj_size = 1024 * 1024
+        tracemalloc.clear_traces()
+        obj, obj_traceback = allocate_bytes(obj_size)
+        size, max_size = tracemalloc.get_traced_memory()
+        self.assertGreaterEqual(size, obj_size)
+        self.assertGreaterEqual(max_size, size)
+
+        self.assertLessEqual(size - obj_size, max_error)
+        self.assertLessEqual(max_size - size, max_error)
+
+        # destroy the object
+        obj = None
+        size2, max_size2 = tracemalloc.get_traced_memory()
+        self.assertLess(size2, size)
+        self.assertGreaterEqual(size - size2, obj_size - max_error)
+        self.assertGreaterEqual(max_size2, max_size)
+
+        # clear_traces() must reset traced memory counters
+        tracemalloc.clear_traces()
+        self.assertEqual(tracemalloc.get_traced_memory(), (0, 0))
+
+        # allocate another object
+        obj, obj_traceback = allocate_bytes(obj_size)
+        size, max_size = tracemalloc.get_traced_memory()
+        self.assertGreater(size, 0)
+
+        # stop() rests also traced memory counters
+        tracemalloc.stop()
+        self.assertEqual(tracemalloc.get_traced_memory(), (0, 0))
+
+    def test_clear_traces(self):
+        obj, obj_traceback = allocate_bytes(123)
+        traceback = tracemalloc.get_object_traceback(obj)
+        self.assertIsNotNone(traceback)
+
+        tracemalloc.clear_traces()
+        traceback2 = tracemalloc.get_object_traceback(obj)
+        self.assertIsNone(traceback2)
+
+    def test_is_tracing(self):
+        tracemalloc.stop()
+        self.assertFalse(tracemalloc.is_tracing())
+
+        tracemalloc.start()
+        self.assertTrue(tracemalloc.is_tracing())
+
+    def test_snapshot(self):
+        obj, source = allocate_bytes(123)
+
+        # take a snapshot
+        snapshot = tracemalloc.take_snapshot()
+
+        # write on disk
+        snapshot.dump(support.TESTFN)
+        self.addCleanup(support.unlink, support.TESTFN)
+
+        # load from disk
+        snapshot2 = tracemalloc.Snapshot.load(support.TESTFN)
+        self.assertEqual(snapshot2.traces, snapshot.traces)
+
+        # tracemalloc must be tracing memory allocations to take a snapshot
+        tracemalloc.stop()
+        with self.assertRaises(RuntimeError) as cm:
+            tracemalloc.take_snapshot()
+        self.assertEqual(str(cm.exception),
+                         "the tracemalloc module must be tracing memory "
+                         "allocations to take a snapshot")
+
+    def test_snapshot_save_attr(self):
+        # take a snapshot with a new attribute
+        snapshot = tracemalloc.take_snapshot()
+        snapshot.test_attr = "new"
+        snapshot.dump(support.TESTFN)
+        self.addCleanup(support.unlink, support.TESTFN)
+
+        # load() should recreates the attribute
+        snapshot2 = tracemalloc.Snapshot.load(support.TESTFN)
+        self.assertEqual(snapshot2.test_attr, "new")
+
+    def fork_child(self):
+        if not tracemalloc.is_tracing():
+            return 2
+
+        obj_size = 12345
+        obj, obj_traceback = allocate_bytes(obj_size)
+        traceback = tracemalloc.get_object_traceback(obj)
+        if traceback is None:
+            return 3
+
+        # everything is fine
+        return 0
+
+    @unittest.skipUnless(hasattr(os, 'fork'), 'need os.fork()')
+    def test_fork(self):
+        # check that tracemalloc is still working after fork
+        pid = os.fork()
+        if not pid:
+            # child
+            exitcode = 1
+            try:
+                exitcode = self.fork_child()
+            finally:
+                os._exit(exitcode)
+        else:
+            pid2, status = os.waitpid(pid, 0)
+            self.assertTrue(os.WIFEXITED(status))
+            exitcode = os.WEXITSTATUS(status)
+            self.assertEqual(exitcode, 0)
+
+
+class TestSnapshot(unittest.TestCase):
+    maxDiff = 4000
+
+    def test_create_snapshot(self):
+        raw_traces = [(5, (('a.py', 2),))]
+
+        with contextlib.ExitStack() as stack:
+            stack.enter_context(patch.object(tracemalloc, 'is_tracing',
+                                             return_value=True))
+            stack.enter_context(patch.object(tracemalloc, 'get_traceback_limit',
+                                             return_value=5))
+            stack.enter_context(patch.object(tracemalloc, '_get_traces',
+                                             return_value=raw_traces))
+
+            snapshot = tracemalloc.take_snapshot()
+            self.assertEqual(snapshot.traceback_limit, 5)
+            self.assertEqual(len(snapshot.traces), 1)
+            trace = snapshot.traces[0]
+            self.assertEqual(trace.size, 5)
+            self.assertEqual(len(trace.traceback), 1)
+            self.assertEqual(trace.traceback[0].filename, 'a.py')
+            self.assertEqual(trace.traceback[0].lineno, 2)
+
+    def test_filter_traces(self):
+        snapshot, snapshot2 = create_snapshots()
+        filter1 = tracemalloc.Filter(False, "b.py")
+        filter2 = tracemalloc.Filter(True, "a.py", 2)
+        filter3 = tracemalloc.Filter(True, "a.py", 5)
+
+        original_traces = list(snapshot.traces._traces)
+
+        # exclude b.py
+        snapshot3 = snapshot.filter_traces((filter1,))
+        self.assertEqual(snapshot3.traces._traces, [
+            (10, (('a.py', 2), ('b.py', 4))),
+            (10, (('a.py', 2), ('b.py', 4))),
+            (10, (('a.py', 2), ('b.py', 4))),
+            (2, (('a.py', 5), ('b.py', 4))),
+            (7, (('<unknown>', 0),)),
+        ])
+
+        # filter_traces() must not touch the original snapshot
+        self.assertEqual(snapshot.traces._traces, original_traces)
+
+        # only include two lines of a.py
+        snapshot4 = snapshot3.filter_traces((filter2, filter3))
+        self.assertEqual(snapshot4.traces._traces, [
+            (10, (('a.py', 2), ('b.py', 4))),
+            (10, (('a.py', 2), ('b.py', 4))),
+            (10, (('a.py', 2), ('b.py', 4))),
+            (2, (('a.py', 5), ('b.py', 4))),
+        ])
+
+        # No filter: just duplicate the snapshot
+        snapshot5 = snapshot.filter_traces(())
+        self.assertIsNot(snapshot5, snapshot)
+        self.assertIsNot(snapshot5.traces, snapshot.traces)
+        self.assertEqual(snapshot5.traces, snapshot.traces)
+
+    def test_snapshot_group_by_line(self):
+        snapshot, snapshot2 = create_snapshots()
+        tb_0 = traceback_lineno('<unknown>', 0)
+        tb_a_2 = traceback_lineno('a.py', 2)
+        tb_a_5 = traceback_lineno('a.py', 5)
+        tb_b_1 = traceback_lineno('b.py', 1)
+        tb_c_578 = traceback_lineno('c.py', 578)
+
+        # stats per file and line
+        stats1 = snapshot.statistics('lineno')
+        self.assertEqual(stats1, [
+            tracemalloc.Statistic(tb_b_1, 66, 1),
+            tracemalloc.Statistic(tb_a_2, 30, 3),
+            tracemalloc.Statistic(tb_0, 7, 1),
+            tracemalloc.Statistic(tb_a_5, 2, 1),
+        ])
+
+        # stats per file and line (2)
+        stats2 = snapshot2.statistics('lineno')
+        self.assertEqual(stats2, [
+            tracemalloc.Statistic(tb_a_5, 5002, 2),
+            tracemalloc.Statistic(tb_c_578, 400, 1),
+            tracemalloc.Statistic(tb_a_2, 30, 3),
+        ])
+
+        # stats diff per file and line
+        statistics = snapshot2.compare_to(snapshot, 'lineno')
+        self.assertEqual(statistics, [
+            tracemalloc.StatisticDiff(tb_a_5, 5002, 5000, 2, 1),
+            tracemalloc.StatisticDiff(tb_c_578, 400, 400, 1, 1),
+            tracemalloc.StatisticDiff(tb_b_1, 0, -66, 0, -1),
+            tracemalloc.StatisticDiff(tb_0, 0, -7, 0, -1),
+            tracemalloc.StatisticDiff(tb_a_2, 30, 0, 3, 0),
+        ])
+
+    def test_snapshot_group_by_file(self):
+        snapshot, snapshot2 = create_snapshots()
+        tb_0 = traceback_filename('<unknown>')
+        tb_a = traceback_filename('a.py')
+        tb_b = traceback_filename('b.py')
+        tb_c = traceback_filename('c.py')
+
+        # stats per file
+        stats1 = snapshot.statistics('filename')
+        self.assertEqual(stats1, [
+            tracemalloc.Statistic(tb_b, 66, 1),
+            tracemalloc.Statistic(tb_a, 32, 4),
+            tracemalloc.Statistic(tb_0, 7, 1),
+        ])
+
+        # stats per file (2)
+        stats2 = snapshot2.statistics('filename')
+        self.assertEqual(stats2, [
+            tracemalloc.Statistic(tb_a, 5032, 5),
+            tracemalloc.Statistic(tb_c, 400, 1),
+        ])
+
+        # stats diff per file
+        diff = snapshot2.compare_to(snapshot, 'filename')
+        self.assertEqual(diff, [
+            tracemalloc.StatisticDiff(tb_a, 5032, 5000, 5, 1),
+            tracemalloc.StatisticDiff(tb_c, 400, 400, 1, 1),
+            tracemalloc.StatisticDiff(tb_b, 0, -66, 0, -1),
+            tracemalloc.StatisticDiff(tb_0, 0, -7, 0, -1),
+        ])
+
+    def test_snapshot_group_by_traceback(self):
+        snapshot, snapshot2 = create_snapshots()
+
+        # stats per file
+        tb1 = traceback(('a.py', 2), ('b.py', 4))
+        tb2 = traceback(('a.py', 5), ('b.py', 4))
+        tb3 = traceback(('b.py', 1))
+        tb4 = traceback(('<unknown>', 0))
+        stats1 = snapshot.statistics('traceback')
+        self.assertEqual(stats1, [
+            tracemalloc.Statistic(tb3, 66, 1),
+            tracemalloc.Statistic(tb1, 30, 3),
+            tracemalloc.Statistic(tb4, 7, 1),
+            tracemalloc.Statistic(tb2, 2, 1),
+        ])
+
+        # stats per file (2)
+        tb5 = traceback(('c.py', 578))
+        stats2 = snapshot2.statistics('traceback')
+        self.assertEqual(stats2, [
+            tracemalloc.Statistic(tb2, 5002, 2),
+            tracemalloc.Statistic(tb5, 400, 1),
+            tracemalloc.Statistic(tb1, 30, 3),
+        ])
+
+        # stats diff per file
+        diff = snapshot2.compare_to(snapshot, 'traceback')
+        self.assertEqual(diff, [
+            tracemalloc.StatisticDiff(tb2, 5002, 5000, 2, 1),
+            tracemalloc.StatisticDiff(tb5, 400, 400, 1, 1),
+            tracemalloc.StatisticDiff(tb3, 0, -66, 0, -1),
+            tracemalloc.StatisticDiff(tb4, 0, -7, 0, -1),
+            tracemalloc.StatisticDiff(tb1, 30, 0, 3, 0),
+        ])
+
+        self.assertRaises(ValueError,
+                          snapshot.statistics, 'traceback', cumulative=True)
+
+    def test_snapshot_group_by_cumulative(self):
+        snapshot, snapshot2 = create_snapshots()
+        tb_0 = traceback_filename('<unknown>')
+        tb_a = traceback_filename('a.py')
+        tb_b = traceback_filename('b.py')
+        tb_a_2 = traceback_lineno('a.py', 2)
+        tb_a_5 = traceback_lineno('a.py', 5)
+        tb_b_1 = traceback_lineno('b.py', 1)
+        tb_b_4 = traceback_lineno('b.py', 4)
+
+        # per file
+        stats = snapshot.statistics('filename', True)
+        self.assertEqual(stats, [
+            tracemalloc.Statistic(tb_b, 98, 5),
+            tracemalloc.Statistic(tb_a, 32, 4),
+            tracemalloc.Statistic(tb_0, 7, 1),
+        ])
+
+        # per line
+        stats = snapshot.statistics('lineno', True)
+        self.assertEqual(stats, [
+            tracemalloc.Statistic(tb_b_1, 66, 1),
+            tracemalloc.Statistic(tb_b_4, 32, 4),
+            tracemalloc.Statistic(tb_a_2, 30, 3),
+            tracemalloc.Statistic(tb_0, 7, 1),
+            tracemalloc.Statistic(tb_a_5, 2, 1),
+        ])
+
+    def test_trace_format(self):
+        snapshot, snapshot2 = create_snapshots()
+        trace = snapshot.traces[0]
+        self.assertEqual(str(trace), 'a.py:2: 10 B')
+        traceback = trace.traceback
+        self.assertEqual(str(traceback), 'a.py:2')
+        frame = traceback[0]
+        self.assertEqual(str(frame), 'a.py:2')
+
+    def test_statistic_format(self):
+        snapshot, snapshot2 = create_snapshots()
+        stats = snapshot.statistics('lineno')
+        stat = stats[0]
+        self.assertEqual(str(stat),
+                         'b.py:1: size=66 B, count=1, average=66 B')
+
+    def test_statistic_diff_format(self):
+        snapshot, snapshot2 = create_snapshots()
+        stats = snapshot2.compare_to(snapshot, 'lineno')
+        stat = stats[0]
+        self.assertEqual(str(stat),
+                         'a.py:5: size=5002 B (+5000 B), count=2 (+1), average=2501 B')
+
+
+
+class TestFilters(unittest.TestCase):
+    maxDiff = 2048
+
+    def test_filter_attributes(self):
+        # test default values
+        f = tracemalloc.Filter(True, "abc")
+        self.assertEqual(f.inclusive, True)
+        self.assertEqual(f.filename_pattern, "abc")
+        self.assertIsNone(f.lineno)
+        self.assertEqual(f.all_frames, False)
+
+        # test custom values
+        f = tracemalloc.Filter(False, "test.py", 123, True)
+        self.assertEqual(f.inclusive, False)
+        self.assertEqual(f.filename_pattern, "test.py")
+        self.assertEqual(f.lineno, 123)
+        self.assertEqual(f.all_frames, True)
+
+        # parameters passed by keyword
+        f = tracemalloc.Filter(inclusive=False, filename_pattern="test.py", lineno=123, all_frames=True)
+        self.assertEqual(f.inclusive, False)
+        self.assertEqual(f.filename_pattern, "test.py")
+        self.assertEqual(f.lineno, 123)
+        self.assertEqual(f.all_frames, True)
+
+        # read-only attribute
+        self.assertRaises(AttributeError, setattr, f, "filename_pattern", "abc")
+
+    def test_filter_match(self):
+        # filter without line number
+        f = tracemalloc.Filter(True, "abc")
+        self.assertTrue(f._match_frame("abc", 0))
+        self.assertTrue(f._match_frame("abc", 5))
+        self.assertTrue(f._match_frame("abc", 10))
+        self.assertFalse(f._match_frame("12356", 0))
+        self.assertFalse(f._match_frame("12356", 5))
+        self.assertFalse(f._match_frame("12356", 10))
+
+        f = tracemalloc.Filter(False, "abc")
+        self.assertFalse(f._match_frame("abc", 0))
+        self.assertFalse(f._match_frame("abc", 5))
+        self.assertFalse(f._match_frame("abc", 10))
+        self.assertTrue(f._match_frame("12356", 0))
+        self.assertTrue(f._match_frame("12356", 5))
+        self.assertTrue(f._match_frame("12356", 10))
+
+        # filter with line number > 0
+        f = tracemalloc.Filter(True, "abc", 5)
+        self.assertFalse(f._match_frame("abc", 0))
+        self.assertTrue(f._match_frame("abc", 5))
+        self.assertFalse(f._match_frame("abc", 10))
+        self.assertFalse(f._match_frame("12356", 0))
+        self.assertFalse(f._match_frame("12356", 5))
+        self.assertFalse(f._match_frame("12356", 10))
+
+        f = tracemalloc.Filter(False, "abc", 5)
+        self.assertTrue(f._match_frame("abc", 0))
+        self.assertFalse(f._match_frame("abc", 5))
+        self.assertTrue(f._match_frame("abc", 10))
+        self.assertTrue(f._match_frame("12356", 0))
+        self.assertTrue(f._match_frame("12356", 5))
+        self.assertTrue(f._match_frame("12356", 10))
+
+        # filter with line number 0
+        f = tracemalloc.Filter(True, "abc", 0)
+        self.assertTrue(f._match_frame("abc", 0))
+        self.assertFalse(f._match_frame("abc", 5))
+        self.assertFalse(f._match_frame("abc", 10))
+        self.assertFalse(f._match_frame("12356", 0))
+        self.assertFalse(f._match_frame("12356", 5))
+        self.assertFalse(f._match_frame("12356", 10))
+
+        f = tracemalloc.Filter(False, "abc", 0)
+        self.assertFalse(f._match_frame("abc", 0))
+        self.assertTrue(f._match_frame("abc", 5))
+        self.assertTrue(f._match_frame("abc", 10))
+        self.assertTrue(f._match_frame("12356", 0))
+        self.assertTrue(f._match_frame("12356", 5))
+        self.assertTrue(f._match_frame("12356", 10))
+
+    def test_filter_match_filename(self):
+        def fnmatch(inclusive, filename, pattern):
+            f = tracemalloc.Filter(inclusive, pattern)
+            return f._match_frame(filename, 0)
+
+        self.assertTrue(fnmatch(True, "abc", "abc"))
+        self.assertFalse(fnmatch(True, "12356", "abc"))
+        self.assertFalse(fnmatch(True, "<unknown>", "abc"))
+
+        self.assertFalse(fnmatch(False, "abc", "abc"))
+        self.assertTrue(fnmatch(False, "12356", "abc"))
+        self.assertTrue(fnmatch(False, "<unknown>", "abc"))
+
+    def test_filter_match_filename_joker(self):
+        def fnmatch(filename, pattern):
+            filter = tracemalloc.Filter(True, pattern)
+            return filter._match_frame(filename, 0)
+
+        # empty string
+        self.assertFalse(fnmatch('abc', ''))
+        self.assertFalse(fnmatch('', 'abc'))
+        self.assertTrue(fnmatch('', ''))
+        self.assertTrue(fnmatch('', '*'))
+
+        # no *
+        self.assertTrue(fnmatch('abc', 'abc'))
+        self.assertFalse(fnmatch('abc', 'abcd'))
+        self.assertFalse(fnmatch('abc', 'def'))
+
+        # a*
+        self.assertTrue(fnmatch('abc', 'a*'))
+        self.assertTrue(fnmatch('abc', 'abc*'))
+        self.assertFalse(fnmatch('abc', 'b*'))
+        self.assertFalse(fnmatch('abc', 'abcd*'))
+
+        # a*b
+        self.assertTrue(fnmatch('abc', 'a*c'))
+        self.assertTrue(fnmatch('abcdcx', 'a*cx'))
+        self.assertFalse(fnmatch('abb', 'a*c'))
+        self.assertFalse(fnmatch('abcdce', 'a*cx'))
+
+        # a*b*c
+        self.assertTrue(fnmatch('abcde', 'a*c*e'))
+        self.assertTrue(fnmatch('abcbdefeg', 'a*bd*eg'))
+        self.assertFalse(fnmatch('abcdd', 'a*c*e'))
+        self.assertFalse(fnmatch('abcbdefef', 'a*bd*eg'))
+
+        # replace .pyc and .pyo suffix with .py
+        self.assertTrue(fnmatch('a.pyc', 'a.py'))
+        self.assertTrue(fnmatch('a.pyo', 'a.py'))
+        self.assertTrue(fnmatch('a.py', 'a.pyc'))
+        self.assertTrue(fnmatch('a.py', 'a.pyo'))
+
+        if os.name == 'nt':
+            # case insensitive
+            self.assertTrue(fnmatch('aBC', 'ABc'))
+            self.assertTrue(fnmatch('aBcDe', 'Ab*dE'))
+
+            self.assertTrue(fnmatch('a.pyc', 'a.PY'))
+            self.assertTrue(fnmatch('a.PYO', 'a.py'))
+            self.assertTrue(fnmatch('a.py', 'a.PYC'))
+            self.assertTrue(fnmatch('a.PY', 'a.pyo'))
+        else:
+            # case sensitive
+            self.assertFalse(fnmatch('aBC', 'ABc'))
+            self.assertFalse(fnmatch('aBcDe', 'Ab*dE'))
+
+            self.assertFalse(fnmatch('a.pyc', 'a.PY'))
+            self.assertFalse(fnmatch('a.PYO', 'a.py'))
+            self.assertFalse(fnmatch('a.py', 'a.PYC'))
+            self.assertFalse(fnmatch('a.PY', 'a.pyo'))
+
+        if os.name == 'nt':
+            # normalize alternate separator "/" to the standard separator "\"
+            self.assertTrue(fnmatch(r'a/b', r'a\b'))
+            self.assertTrue(fnmatch(r'a\b', r'a/b'))
+            self.assertTrue(fnmatch(r'a/b\c', r'a\b/c'))
+            self.assertTrue(fnmatch(r'a/b/c', r'a\b\c'))
+        else:
+            # there is no alternate separator
+            self.assertFalse(fnmatch(r'a/b', r'a\b'))
+            self.assertFalse(fnmatch(r'a\b', r'a/b'))
+            self.assertFalse(fnmatch(r'a/b\c', r'a\b/c'))
+            self.assertFalse(fnmatch(r'a/b/c', r'a\b\c'))
+
+    def test_filter_match_trace(self):
+        t1 = (("a.py", 2), ("b.py", 3))
+        t2 = (("b.py", 4), ("b.py", 5))
+        t3 = (("c.py", 5), ('<unknown>', 0))
+        unknown = (('<unknown>', 0),)
+
+        f = tracemalloc.Filter(True, "b.py", all_frames=True)
+        self.assertTrue(f._match_traceback(t1))
+        self.assertTrue(f._match_traceback(t2))
+        self.assertFalse(f._match_traceback(t3))
+        self.assertFalse(f._match_traceback(unknown))
+
+        f = tracemalloc.Filter(True, "b.py", all_frames=False)
+        self.assertFalse(f._match_traceback(t1))
+        self.assertTrue(f._match_traceback(t2))
+        self.assertFalse(f._match_traceback(t3))
+        self.assertFalse(f._match_traceback(unknown))
+
+        f = tracemalloc.Filter(False, "b.py", all_frames=True)
+        self.assertFalse(f._match_traceback(t1))
+        self.assertFalse(f._match_traceback(t2))
+        self.assertTrue(f._match_traceback(t3))
+        self.assertTrue(f._match_traceback(unknown))
+
+        f = tracemalloc.Filter(False, "b.py", all_frames=False)
+        self.assertTrue(f._match_traceback(t1))
+        self.assertFalse(f._match_traceback(t2))
+        self.assertTrue(f._match_traceback(t3))
+        self.assertTrue(f._match_traceback(unknown))
+
+        f = tracemalloc.Filter(False, "<unknown>", all_frames=False)
+        self.assertTrue(f._match_traceback(t1))
+        self.assertTrue(f._match_traceback(t2))
+        self.assertTrue(f._match_traceback(t3))
+        self.assertFalse(f._match_traceback(unknown))
+
+        f = tracemalloc.Filter(True, "<unknown>", all_frames=True)
+        self.assertFalse(f._match_traceback(t1))
+        self.assertFalse(f._match_traceback(t2))
+        self.assertTrue(f._match_traceback(t3))
+        self.assertTrue(f._match_traceback(unknown))
+
+        f = tracemalloc.Filter(False, "<unknown>", all_frames=True)
+        self.assertTrue(f._match_traceback(t1))
+        self.assertTrue(f._match_traceback(t2))
+        self.assertFalse(f._match_traceback(t3))
+        self.assertFalse(f._match_traceback(unknown))
+
+
+class TestCommandLine(unittest.TestCase):
+    def test_env_var(self):
+        # not tracing by default
+        code = 'import tracemalloc; print(tracemalloc.is_tracing())'
+        ok, stdout, stderr = assert_python_ok('-c', code)
+        stdout = stdout.rstrip()
+        self.assertEqual(stdout, b'False')
+
+        # PYTHON* environment varibles must be ignored when -E option is
+        # present
+        code = 'import tracemalloc; print(tracemalloc.is_tracing())'
+        ok, stdout, stderr = assert_python_ok('-E', '-c', code, PYTHONTRACEMALLOC='1')
+        stdout = stdout.rstrip()
+        self.assertEqual(stdout, b'False')
+
+        # tracing at startup
+        code = 'import tracemalloc; print(tracemalloc.is_tracing())'
+        ok, stdout, stderr = assert_python_ok('-c', code, PYTHONTRACEMALLOC='1')
+        stdout = stdout.rstrip()
+        self.assertEqual(stdout, b'True')
+
+        # start and set the number of frames
+        code = 'import tracemalloc; print(tracemalloc.get_traceback_limit())'
+        ok, stdout, stderr = assert_python_ok('-c', code, PYTHONTRACEMALLOC='10')
+        stdout = stdout.rstrip()
+        self.assertEqual(stdout, b'10')
+
+    def test_env_var_invalid(self):
+        for nframe in (-1, 0, 5000):
+            with self.subTest(nframe=nframe):
+                with support.SuppressCrashReport():
+                    ok, stdout, stderr = assert_python_failure(
+                        '-c', 'pass',
+                        PYTHONTRACEMALLOC=str(nframe))
+                    self.assertIn(b'PYTHONTRACEMALLOC must be an integer '
+                                  b'in range [1; 100]',
+                                  stderr)
+
+    def test_sys_xoptions(self):
+        for xoptions, nframe in (
+            ('tracemalloc', 1),
+            ('tracemalloc=1', 1),
+            ('tracemalloc=15', 15),
+        ):
+            with self.subTest(xoptions=xoptions, nframe=nframe):
+                code = 'import tracemalloc; print(tracemalloc.get_traceback_limit())'
+                ok, stdout, stderr = assert_python_ok('-X', xoptions, '-c', code)
+                stdout = stdout.rstrip()
+                self.assertEqual(stdout, str(nframe).encode('ascii'))
+
+    def test_sys_xoptions_invalid(self):
+        for nframe in (-1, 0, 5000):
+            with self.subTest(nframe=nframe):
+                with support.SuppressCrashReport():
+                    args = ('-X', 'tracemalloc=%s' % nframe, '-c', 'pass')
+                    ok, stdout, stderr = assert_python_failure(*args)
+                    self.assertIn(b'-X tracemalloc=NFRAME: number of frame must '
+                                  b'be an integer in range [1; 100]',
+                                  stderr)
+
+
+def test_main():
+    support.run_unittest(
+        TestTracemallocEnabled,
+        TestSnapshot,
+        TestFilters,
+        TestCommandLine,
+    )
+
+if __name__ == "__main__":
+    test_main()
diff --git a/Lib/tracemalloc.py b/Lib/tracemalloc.py
new file mode 100644
index 0000000..7780eca
--- /dev/null
+++ b/Lib/tracemalloc.py
@@ -0,0 +1,464 @@
+from collections import Sequence
+from functools import total_ordering
+import fnmatch
+import os.path
+import pickle
+
+# Import types and functions implemented in C
+from _tracemalloc import *
+from _tracemalloc import _get_object_traceback, _get_traces
+
+
+def _format_size(size, sign):
+    for unit in ('B', 'KiB', 'MiB', 'GiB', 'TiB'):
+        if abs(size) < 100 and unit != 'B':
+            # 3 digits (xx.x UNIT)
+            if sign:
+                return "%+.1f %s" % (size, unit)
+            else:
+                return "%.1f %s" % (size, unit)
+        if abs(size) < 10 * 1024 or unit == 'TiB':
+            # 4 or 5 digits (xxxx UNIT)
+            if sign:
+                return "%+.0f %s" % (size, unit)
+            else:
+                return "%.0f %s" % (size, unit)
+        size /= 1024
+
+
+class Statistic:
+    """
+    Statistic difference on memory allocations between two Snapshot instance.
+    """
+
+    __slots__ = ('traceback', 'size', 'count')
+
+    def __init__(self, traceback, size, count):
+        self.traceback = traceback
+        self.size = size
+        self.count = count
+
+    def __hash__(self):
+        return (self.traceback, self.size, self.count)
+
+    def __eq__(self, other):
+        return (self.traceback == other.traceback
+                and self.size == other.size
+                and self.count == other.count)
+
+    def __str__(self):
+        text = ("%s: size=%s, count=%i"
+                 % (self.traceback,
+                    _format_size(self.size, False),
+                    self.count))
+        if self.count:
+            average = self.size / self.count
+            text += ", average=%s" % _format_size(average, False)
+        return text
+
+    def __repr__(self):
+        return ('<Statistic traceback=%r size=%i count=%i>'
+                % (self.traceback, self.size, self.count))
+
+    def _sort_key(self):
+        return (self.size, self.count, self.traceback)
+
+
+class StatisticDiff:
+    """
+    Statistic difference on memory allocations between an old and a new
+    Snapshot instance.
+    """
+    __slots__ = ('traceback', 'size', 'size_diff', 'count', 'count_diff')
+
+    def __init__(self, traceback, size, size_diff, count, count_diff):
+        self.traceback = traceback
+        self.size = size
+        self.size_diff = size_diff
+        self.count = count
+        self.count_diff = count_diff
+
+    def __hash__(self):
+        return (self.traceback, self.size, self.size_diff,
+                self.count, self.count_diff)
+
+    def __eq__(self, other):
+        return (self.traceback == other.traceback
+                and self.size == other.size
+                and self.size_diff == other.size_diff
+                and self.count == other.count
+                and self.count_diff == other.count_diff)
+
+    def __str__(self):
+        text = ("%s: size=%s (%s), count=%i (%+i)"
+                % (self.traceback,
+                   _format_size(self.size, False),
+                   _format_size(self.size_diff, True),
+                   self.count,
+                   self.count_diff))
+        if self.count:
+            average = self.size / self.count
+            text += ", average=%s" % _format_size(average, False)
+        return text
+
+    def __repr__(self):
+        return ('<StatisticDiff traceback=%r size=%i (%+i) count=%i (%+i)>'
+                % (self.traceback, self.size, self.size_diff,
+
+                   self.count, self.count_diff))
+
+    def _sort_key(self):
+        return (abs(self.size_diff), self.size,
+                abs(self.count_diff), self.count,
+                self.traceback)
+
+
+def _compare_grouped_stats(old_group, new_group):
+    statistics = []
+    for traceback, stat in new_group.items():
+        previous = old_group.pop(traceback, None)
+        if previous is not None:
+            stat = StatisticDiff(traceback,
+                                  stat.size, stat.size - previous.size,
+                                  stat.count, stat.count - previous.count)
+        else:
+            stat = StatisticDiff(traceback,
+                                  stat.size, stat.size,
+                                  stat.count, stat.count)
+        statistics.append(stat)
+
+    for traceback, stat in old_group.items():
+        stat = StatisticDiff(traceback, 0, -stat.size, 0, -stat.count)
+        statistics.append(stat)
+    return statistics
+
+
+@total_ordering
+class Frame:
+    """
+    Frame of a traceback.
+    """
+    __slots__ = ("_frame",)
+
+    def __init__(self, frame):
+        self._frame = frame
+
+    @property
+    def filename(self):
+        return self._frame[0]
+
+    @property
+    def lineno(self):
+        return self._frame[1]
+
+    def __eq__(self, other):
+        return (self._frame == other._frame)
+
+    def __lt__(self, other):
+        return (self._frame < other._frame)
+
+    def __hash__(self):
+        return hash(self._frame)
+
+    def __str__(self):
+        return "%s:%s" % (self.filename, self.lineno)
+
+    def __repr__(self):
+        return "<Frame filename=%r lineno=%r>" % (self.filename, self.lineno)
+
+
+@total_ordering
+class Traceback(Sequence):
+    """
+    Sequence of Frame instances sorted from the most recent frame
+    to the oldest frame.
+    """
+    __slots__ = ("_frames",)
+
+    def __init__(self, frames):
+        Sequence.__init__(self)
+        self._frames = frames
+
+    def __len__(self):
+        return len(self._frames)
+
+    def __getitem__(self, index):
+        trace = self._frames[index]
+        return Frame(trace)
+
+    def __contains__(self, frame):
+        return frame._frame in self._frames
+
+    def __hash__(self):
+        return hash(self._frames)
+
+    def __eq__(self, other):
+        return (self._frames == other._frames)
+
+    def __lt__(self, other):
+        return (self._frames < other._frames)
+
+    def __str__(self):
+        return str(self[0])
+
+    def __repr__(self):
+        return "<Traceback %r>" % (tuple(self),)
+
+
+def get_object_traceback(obj):
+    """
+    Get the traceback where the Python object *obj* was allocated.
+    Return a Traceback instance.
+
+    Return None if the tracemalloc module is not tracing memory allocations or
+    did not trace the allocation of the object.
+    """
+    frames = _get_object_traceback(obj)
+    if frames is not None:
+        return Traceback(frames)
+    else:
+        return None
+
+
+class Trace:
+    """
+    Trace of a memory block.
+    """
+    __slots__ = ("_trace",)
+
+    def __init__(self, trace):
+        self._trace = trace
+
+    @property
+    def size(self):
+        return self._trace[0]
+
+    @property
+    def traceback(self):
+        return Traceback(self._trace[1])
+
+    def __eq__(self, other):
+        return (self._trace == other._trace)
+
+    def __hash__(self):
+        return hash(self._trace)
+
+    def __str__(self):
+        return "%s: %s" % (self.traceback, _format_size(self.size, False))
+
+    def __repr__(self):
+        return ("<Trace size=%s, traceback=%r>"
+                % (_format_size(self.size, False), self.traceback))
+
+
+class _Traces(Sequence):
+    def __init__(self, traces):
+        Sequence.__init__(self)
+        self._traces = traces
+
+    def __len__(self):
+        return len(self._traces)
+
+    def __getitem__(self, index):
+        trace = self._traces[index]
+        return Trace(trace)
+
+    def __contains__(self, trace):
+        return trace._trace in self._traces
+
+    def __eq__(self, other):
+        return (self._traces == other._traces)
+
+    def __repr__(self):
+        return "<Traces len=%s>" % len(self)
+
+
+def _normalize_filename(filename):
+    filename = os.path.normcase(filename)
+    if filename.endswith(('.pyc', '.pyo')):
+        filename = filename[:-1]
+    return filename
+
+
+class Filter:
+    def __init__(self, inclusive, filename_pattern,
+                 lineno=None, all_frames=False):
+        self.inclusive = inclusive
+        self._filename_pattern = _normalize_filename(filename_pattern)
+        self.lineno = lineno
+        self.all_frames = all_frames
+
+    @property
+    def filename_pattern(self):
+        return self._filename_pattern
+
+    def __match_frame(self, filename, lineno):
+        filename = _normalize_filename(filename)
+        if not fnmatch.fnmatch(filename, self._filename_pattern):
+            return False
+        if self.lineno is None:
+            return True
+        else:
+            return (lineno == self.lineno)
+
+    def _match_frame(self, filename, lineno):
+        return self.__match_frame(filename, lineno) ^ (not self.inclusive)
+
+    def _match_traceback(self, traceback):
+        if self.all_frames:
+            if any(self.__match_frame(filename, lineno)
+                   for filename, lineno in traceback):
+                return self.inclusive
+            else:
+                return (not self.inclusive)
+        else:
+            filename, lineno = traceback[0]
+            return self._match_frame(filename, lineno)
+
+
+class Snapshot:
+    """
+    Snapshot of traces of memory blocks allocated by Python.
+    """
+
+    def __init__(self, traces, traceback_limit):
+        self.traces = _Traces(traces)
+        self.traceback_limit = traceback_limit
+
+    def dump(self, filename):
+        """
+        Write the snapshot into a file.
+        """
+        with open(filename, "wb") as fp:
+            pickle.dump(self, fp, pickle.HIGHEST_PROTOCOL)
+
+    @staticmethod
+    def load(filename):
+        """
+        Load a snapshot from a file.
+        """
+        with open(filename, "rb") as fp:
+            return pickle.load(fp)
+
+    def _filter_trace(self, include_filters, exclude_filters, trace):
+        traceback = trace[1]
+        if include_filters:
+            if not any(trace_filter._match_traceback(traceback)
+                       for trace_filter in include_filters):
+                return False
+        if exclude_filters:
+            if any(not trace_filter._match_traceback(traceback)
+                   for trace_filter in exclude_filters):
+                return False
+        return True
+
+    def filter_traces(self, filters):
+        """
+        Create a new Snapshot instance with a filtered traces sequence, filters
+        is a list of Filter instances.  If filters is an empty list, return a
+        new Snapshot instance with a copy of the traces.
+        """
+        if filters:
+            include_filters = []
+            exclude_filters = []
+            for trace_filter in filters:
+                if trace_filter.inclusive:
+                    include_filters.append(trace_filter)
+                else:
+                    exclude_filters.append(trace_filter)
+            new_traces = [trace for trace in self.traces._traces
+                          if self._filter_trace(include_filters,
+                                                exclude_filters,
+                                                trace)]
+        else:
+            new_traces = self.traces._traces.copy()
+        return Snapshot(new_traces, self.traceback_limit)
+
+    def _group_by(self, key_type, cumulative):
+        if key_type not in ('traceback', 'filename', 'lineno'):
+            raise ValueError("unknown key_type: %r" % (key_type,))
+        if cumulative and key_type not in ('lineno', 'filename'):
+            raise ValueError("cumulative mode cannot by used "
+                             "with key type %r" % key_type)
+        if cumulative and self.traceback_limit < 2:
+            raise ValueError("cumulative mode needs tracebacks with at least "
+                             "2 frames, traceback limit is %s"
+                             % self.traceback_limit)
+
+        stats = {}
+        tracebacks = {}
+        if not cumulative:
+            for trace in self.traces._traces:
+                size, trace_traceback = trace
+                try:
+                    traceback = tracebacks[trace_traceback]
+                except KeyError:
+                    if key_type == 'traceback':
+                        frames = trace_traceback
+                    elif key_type == 'lineno':
+                        frames = trace_traceback[:1]
+                    else: # key_type == 'filename':
+                        frames = ((trace_traceback[0][0], 0),)
+                    traceback = Traceback(frames)
+                    tracebacks[trace_traceback] = traceback
+                try:
+                    stat = stats[traceback]
+                    stat.size += size
+                    stat.count += 1
+                except KeyError:
+                    stats[traceback] = Statistic(traceback, size, 1)
+        else:
+            # cumulative statistics
+            for trace in self.traces._traces:
+                size, trace_traceback = trace
+                for frame in trace_traceback:
+                    try:
+                        traceback = tracebacks[frame]
+                    except KeyError:
+                        if key_type == 'lineno':
+                            frames = (frame,)
+                        else: # key_type == 'filename':
+                            frames = ((frame[0], 0),)
+                        traceback = Traceback(frames)
+                        tracebacks[frame] = traceback
+                    try:
+                        stat = stats[traceback]
+                        stat.size += size
+                        stat.count += 1
+                    except KeyError:
+                        stats[traceback] = Statistic(traceback, size, 1)
+        return stats
+
+    def statistics(self, key_type, cumulative=False):
+        """
+        Group statistics by key_type. Return a sorted list of Statistic
+        instances.
+        """
+        grouped = self._group_by(key_type, cumulative)
+        statistics = list(grouped.values())
+        statistics.sort(reverse=True, key=Statistic._sort_key)
+        return statistics
+
+    def compare_to(self, old_snapshot, key_type, cumulative=False):
+        """
+        Compute the differences with an old snapshot old_snapshot. Get
+        statistics as a sorted list of StatisticDiff instances, grouped by
+        group_by.
+        """
+        new_group = self._group_by(key_type, cumulative)
+        old_group = old_snapshot._group_by(key_type, cumulative)
+        statistics = _compare_grouped_stats(old_group, new_group)
+        statistics.sort(reverse=True, key=StatisticDiff._sort_key)
+        return statistics
+
+
+def take_snapshot():
+    """
+    Take a snapshot of traces of memory blocks allocated by Python.
+    """
+    if not is_tracing():
+        raise RuntimeError("the tracemalloc module must be tracing memory "
+                           "allocations to take a snapshot")
+    traces = _get_traces()
+    traceback_limit = get_traceback_limit()
+    return Snapshot(traces, traceback_limit)