:mod:`!tracemalloc` --- Trace memory allocations
.. module:: tracemalloc :synopsis: Trace memory allocations.
.. versionadded:: 3.4
Source code: :source:`Lib/tracemalloc.py`
The tracemalloc module is a debug tool to trace memory blocks allocated by Python. It provides the following information:
- Traceback where an object was allocated
- Statistics on allocated memory blocks per filename and per line number: total size, number and average size of allocated memory blocks
- Compute the differences between two snapshots to detect memory leaks
To trace most memory blocks allocated by Python, the module should be started
as early as possible by setting the :envvar:`PYTHONTRACEMALLOC` environment
variable to 1, or by using :option:`-X` tracemalloc command line
option. The :func:`tracemalloc.start` function can be called at runtime to
start tracing Python memory allocations.
By default, a trace of an allocated memory block only stores the most recent
frame (1 frame). To store 25 frames at startup: set the
:envvar:`PYTHONTRACEMALLOC` environment variable to 25, or use the
:option:`-X` tracemalloc=25 command line option.
Display the 10 files allocating the most memory:
import tracemalloc
tracemalloc.start()
# ... run your application ...
snapshot = tracemalloc.take_snapshot()
top_stats = snapshot.statistics('lineno')
print("[ Top 10 ]")
for stat in top_stats[:10]:
print(stat)
Example of output of the Python test suite:
[ Top 10 ] <frozen importlib._bootstrap>:716: size=4855 KiB, count=39328, average=126 B <frozen importlib._bootstrap>:284: size=521 KiB, count=3199, average=167 B /usr/lib/python3.4/collections/__init__.py:368: size=244 KiB, count=2315, average=108 B /usr/lib/python3.4/unittest/case.py:381: size=185 KiB, count=779, average=243 B /usr/lib/python3.4/unittest/case.py:402: size=154 KiB, count=378, average=416 B /usr/lib/python3.4/abc.py:133: size=88.7 KiB, count=347, average=262 B <frozen importlib._bootstrap>:1446: size=70.4 KiB, count=911, average=79 B <frozen importlib._bootstrap>:1454: size=52.0 KiB, count=25, average=2131 B <string>:5: size=49.7 KiB, count=148, average=344 B /usr/lib/python3.4/sysconfig.py:411: size=48.0 KiB, count=1, average=48.0 KiB
We can see that Python loaded 4855 KiB data (bytecode and constants) from
modules and that the :mod:`collections` module allocated 244 KiB to build
:class:`~collections.namedtuple` types.
See :meth:`Snapshot.statistics` for more options.
Take two snapshots and display the differences:
import tracemalloc
tracemalloc.start()
# ... start your application ...
snapshot1 = tracemalloc.take_snapshot()
# ... call the function leaking memory ...
snapshot2 = tracemalloc.take_snapshot()
top_stats = snapshot2.compare_to(snapshot1, 'lineno')
print("[ Top 10 differences ]")
for stat in top_stats[:10]:
print(stat)
Example of output before/after running some tests of the Python test suite:
[ Top 10 differences ] <frozen importlib._bootstrap>:716: size=8173 KiB (+4428 KiB), count=71332 (+39369), average=117 B /usr/lib/python3.4/linecache.py:127: size=940 KiB (+940 KiB), count=8106 (+8106), average=119 B /usr/lib/python3.4/unittest/case.py:571: size=298 KiB (+298 KiB), count=589 (+589), average=519 B <frozen importlib._bootstrap>:284: size=1005 KiB (+166 KiB), count=7423 (+1526), average=139 B /usr/lib/python3.4/mimetypes.py:217: size=112 KiB (+112 KiB), count=1334 (+1334), average=86 B /usr/lib/python3.4/http/server.py:848: size=96.0 KiB (+96.0 KiB), count=1 (+1), average=96.0 KiB /usr/lib/python3.4/inspect.py:1465: size=83.5 KiB (+83.5 KiB), count=109 (+109), average=784 B /usr/lib/python3.4/unittest/mock.py:491: size=77.7 KiB (+77.7 KiB), count=143 (+143), average=557 B /usr/lib/python3.4/urllib/parse.py:476: size=71.8 KiB (+71.8 KiB), count=969 (+969), average=76 B /usr/lib/python3.4/contextlib.py:38: size=67.2 KiB (+67.2 KiB), count=126 (+126), average=546 B
We can see that Python has loaded 8173 KiB of module data (bytecode and
constants), and that this is 4428 KiB more than had been loaded before the
tests, when the previous snapshot was taken. Similarly, the :mod:`linecache`
module has cached 940 KiB of Python source code to format tracebacks, all
of it since the previous snapshot.
If the system has little free memory, snapshots can be written on disk using the :meth:`Snapshot.dump` method to analyze the snapshot offline. Then use the :meth:`Snapshot.load` method reload the snapshot.
Code to display the traceback of the biggest memory block:
import tracemalloc
# Store 25 frames
tracemalloc.start(25)
# ... run your application ...
snapshot = tracemalloc.take_snapshot()
top_stats = snapshot.statistics('traceback')
# pick the biggest memory block
stat = top_stats[0]
print("%s memory blocks: %.1f KiB" % (stat.count, stat.size / 1024))
for line in stat.traceback.format():
print(line)
Example of output of the Python test suite (traceback limited to 25 frames):
903 memory blocks: 870.1 KiB
File "<frozen importlib._bootstrap>", line 716
File "<frozen importlib._bootstrap>", line 1036
File "<frozen importlib._bootstrap>", line 934
File "<frozen importlib._bootstrap>", line 1068
File "<frozen importlib._bootstrap>", line 619
File "<frozen importlib._bootstrap>", line 1581
File "<frozen importlib._bootstrap>", line 1614
File "/usr/lib/python3.4/doctest.py", line 101
import pdb
File "<frozen importlib._bootstrap>", line 284
File "<frozen importlib._bootstrap>", line 938
File "<frozen importlib._bootstrap>", line 1068
File "<frozen importlib._bootstrap>", line 619
File "<frozen importlib._bootstrap>", line 1581
File "<frozen importlib._bootstrap>", line 1614
File "/usr/lib/python3.4/test/support/__init__.py", line 1728
import doctest
File "/usr/lib/python3.4/test/test_pickletools.py", line 21
support.run_doctest(pickletools)
File "/usr/lib/python3.4/test/regrtest.py", line 1276
test_runner()
File "/usr/lib/python3.4/test/regrtest.py", line 976
display_failure=not verbose)
File "/usr/lib/python3.4/test/regrtest.py", line 761
match_tests=ns.match_tests)
File "/usr/lib/python3.4/test/regrtest.py", line 1563
main()
File "/usr/lib/python3.4/test/__main__.py", line 3
regrtest.main_in_temp_cwd()
File "/usr/lib/python3.4/runpy.py", line 73
exec(code, run_globals)
File "/usr/lib/python3.4/runpy.py", line 160
"__main__", fname, loader, pkg_name)
We can see that the most memory was allocated in the :mod:`importlib` module to
load data (bytecode and constants) from modules: 870.1 KiB. The traceback is
where the :mod:`importlib` loaded data most recently: on the import pdb
line of the :mod:`doctest` module. The traceback may change if a new module is
loaded.
Code to display the 10 lines allocating the most memory with a pretty output,
ignoring <frozen importlib._bootstrap> and <unknown> files:
import linecache
import os
import tracemalloc
def display_top(snapshot, key_type='lineno', limit=10):
snapshot = snapshot.filter_traces((
tracemalloc.Filter(False, "<frozen importlib._bootstrap>"),
tracemalloc.Filter(False, "<unknown>"),
))
top_stats = snapshot.statistics(key_type)
print("Top %s lines" % limit)
for index, stat in enumerate(top_stats[:limit], 1):
frame = stat.traceback[0]
print("#%s: %s:%s: %.1f KiB"
% (index, frame.filename, frame.lineno, stat.size / 1024))
line = linecache.getline(frame.filename, frame.lineno).strip()
if line:
print(' %s' % line)
other = top_stats[limit:]
if other:
size = sum(stat.size for stat in other)
print("%s other: %.1f KiB" % (len(other), size / 1024))
total = sum(stat.size for stat in top_stats)
print("Total allocated size: %.1f KiB" % (total / 1024))
tracemalloc.start()
# ... run your application ...
snapshot = tracemalloc.take_snapshot()
display_top(snapshot)
Example of output of the Python test suite:
Top 10 lines
#1: Lib/base64.py:414: 419.8 KiB
_b85chars2 = [(a + b) for a in _b85chars for b in _b85chars]
#2: Lib/base64.py:306: 419.8 KiB
_a85chars2 = [(a + b) for a in _a85chars for b in _a85chars]
#3: collections/__init__.py:368: 293.6 KiB
exec(class_definition, namespace)
#4: Lib/abc.py:133: 115.2 KiB
cls = super().__new__(mcls, name, bases, namespace)
#5: unittest/case.py:574: 103.1 KiB
testMethod()
#6: Lib/linecache.py:127: 95.4 KiB
lines = fp.readlines()
#7: urllib/parse.py:476: 71.8 KiB
for a in _hexdig for b in _hexdig}
#8: <string>:5: 62.0 KiB
#9: Lib/_weakrefset.py:37: 60.0 KiB
self.data = set()
#10: Lib/base64.py:142: 59.8 KiB
_b32tab2 = [a + b for a in _b32tab for b in _b32tab]
6220 other: 3602.8 KiB
Total allocated size: 5303.1 KiB
See :meth:`Snapshot.statistics` for more options.
The following code computes two sums like 0 + 1 + 2 + ... inefficiently, by
creating a list of those numbers. This list consumes a lot of memory
temporarily. We can use :func:`get_traced_memory` and :func:`reset_peak` to
observe the small memory usage after the sum is computed as well as the peak
memory usage during the computations:
import tracemalloc
tracemalloc.start()
# Example code: compute a sum with a large temporary list
large_sum = sum(list(range(100000)))
first_size, first_peak = tracemalloc.get_traced_memory()
tracemalloc.reset_peak()
# Example code: compute a sum with a small temporary list
small_sum = sum(list(range(1000)))
second_size, second_peak = tracemalloc.get_traced_memory()
print(f"{first_size=}, {first_peak=}")
print(f"{second_size=}, {second_peak=}")
Output:
first_size=664, first_peak=3592984 second_size=804, second_peak=29704
Using :func:`reset_peak` ensured we could accurately record the peak during the
computation of small_sum, even though it is much smaller than the overall
peak size of memory blocks since the :func:`start` call. Without the call to
:func:`reset_peak`, second_peak would still be the peak from the
computation large_sum (that is, equal to first_peak). In this case,
both peaks are much higher than the final memory usage, and which suggests we
could optimise (by removing the unnecessary call to :class:`list`, and writing
sum(range(...))).
.. function:: clear_traces() Clear traces of memory blocks allocated by Python. See also :func:`stop`.
.. function:: get_object_traceback(obj) Get the traceback where the Python object *obj* was allocated. Return a :class:`Traceback` instance, or ``None`` if the :mod:`tracemalloc` module is not tracing memory allocations or did not trace the allocation of the object. See also :func:`gc.get_referrers` and :func:`sys.getsizeof` functions.
.. function:: get_traceback_limit() Get the maximum number of frames stored in the traceback of a trace. The :mod:`tracemalloc` module must be tracing memory allocations to get the limit, otherwise an exception is raised. The limit is set by the :func:`start` function.
.. function:: get_traced_memory() Get the current size and peak size of memory blocks traced by the :mod:`tracemalloc` module as a tuple: ``(current: int, peak: int)``.
.. function:: reset_peak() Set the peak size of memory blocks traced by the :mod:`tracemalloc` module to the current size. Do nothing if the :mod:`tracemalloc` module is not tracing memory allocations. This function only modifies the recorded peak size, and does not modify or clear any traces, unlike :func:`clear_traces`. Snapshots taken with :func:`take_snapshot` before a call to :func:`reset_peak` can be meaningfully compared to snapshots taken after the call. See also :func:`get_traced_memory`. .. versionadded:: 3.9
.. function:: get_tracemalloc_memory() Get the memory usage in bytes of the :mod:`tracemalloc` module used to store traces of memory blocks. Return an :class:`int`.
.. function:: is_tracing()
``True`` if the :mod:`tracemalloc` module is tracing Python memory
allocations, ``False`` otherwise.
See also :func:`start` and :func:`stop` functions.
.. function:: start(nframe: int=1) Start tracing Python memory allocations: install hooks on Python memory allocators. Collected tracebacks of traces will be limited to *nframe* frames. By default, a trace of a memory block only stores the most recent frame: the limit is ``1``. *nframe* must be greater or equal to ``1``. You can still read the original number of total frames that composed the traceback by looking at the :attr:`Traceback.total_nframe` attribute. Storing more than ``1`` frame is only useful to compute statistics grouped by ``'traceback'`` or to compute cumulative statistics: see the :meth:`Snapshot.compare_to` and :meth:`Snapshot.statistics` methods. Storing more frames increases the memory and CPU overhead of the :mod:`tracemalloc` module. Use the :func:`get_tracemalloc_memory` function to measure how much memory is used by the :mod:`tracemalloc` module. The :envvar:`PYTHONTRACEMALLOC` environment variable (``PYTHONTRACEMALLOC=NFRAME``) and the :option:`-X` ``tracemalloc=NFRAME`` command line option can be used to start tracing at startup. See also :func:`stop`, :func:`is_tracing` and :func:`get_traceback_limit` functions.
.. function:: stop() Stop tracing Python memory allocations: uninstall hooks on Python memory allocators. Also clears all previously collected traces of memory blocks allocated by Python. Call :func:`take_snapshot` function to take a snapshot of traces before clearing them. See also :func:`start`, :func:`is_tracing` and :func:`clear_traces` functions.
.. function:: take_snapshot() Take a snapshot of traces of memory blocks allocated by Python. Return a new :class:`Snapshot` instance. The snapshot does not include memory blocks allocated before the :mod:`tracemalloc` module started to trace memory allocations. Tracebacks of traces are limited to :func:`get_traceback_limit` frames. Use the *nframe* parameter of the :func:`start` function to store more frames. The :mod:`tracemalloc` module must be tracing memory allocations to take a snapshot, see the :func:`start` function. See also the :func:`get_object_traceback` function.
Filter traces of memory blocks by their address space (domain).
.. versionadded:: 3.6
.. attribute:: inclusive If *inclusive* is ``True`` (include), match memory blocks allocated in the address space :attr:`domain`. If *inclusive* is ``False`` (exclude), match memory blocks not allocated in the address space :attr:`domain`.
.. attribute:: domain Address space of a memory block (``int``). Read-only property.
Filter on traces of memory blocks.
See the :func:`fnmatch.fnmatch` function for the syntax of
filename_pattern. The '.pyc' file extension is
replaced with '.py'.
Examples:
Filter(True, subprocess.__file__)only includes traces of the :mod:`subprocess` moduleFilter(False, tracemalloc.__file__)excludes traces of the :mod:`tracemalloc` moduleFilter(False, "<unknown>")excludes empty tracebacks
.. versionchanged:: 3.5 The ``'.pyo'`` file extension is no longer replaced with ``'.py'``.
.. versionchanged:: 3.6 Added the :attr:`domain` attribute.
.. attribute:: domain Address space of a memory block (``int`` or ``None``). tracemalloc uses the domain ``0`` to trace memory allocations made by Python. C extensions can use other domains to trace other resources.
.. attribute:: inclusive If *inclusive* is ``True`` (include), only match memory blocks allocated in a file with a name matching :attr:`filename_pattern` at line number :attr:`lineno`. If *inclusive* is ``False`` (exclude), ignore memory blocks allocated in a file with a name matching :attr:`filename_pattern` at line number :attr:`lineno`.
.. attribute:: lineno Line number (``int``) of the filter. If *lineno* is ``None``, the filter matches any line number.
.. attribute:: filename_pattern Filename pattern of the filter (``str``). Read-only property.
.. attribute:: all_frames If *all_frames* is ``True``, all frames of the traceback are checked. If *all_frames* is ``False``, only the most recent frame is checked. This attribute has no effect if the traceback limit is ``1``. See the :func:`get_traceback_limit` function and :attr:`Snapshot.traceback_limit` attribute.
Frame of a traceback.
The :class:`Traceback` class is a sequence of :class:`Frame` instances.
.. attribute:: filename Filename (``str``).
.. attribute:: lineno Line number (``int``).
Snapshot of traces of memory blocks allocated by Python.
The :func:`take_snapshot` function creates a snapshot instance.
.. method:: compare_to(old_snapshot: Snapshot, key_type: str, cumulative: bool=False) Compute the differences with an old snapshot. Get statistics as a sorted list of :class:`StatisticDiff` instances grouped by *key_type*. See the :meth:`Snapshot.statistics` method for *key_type* and *cumulative* parameters. The result is sorted from the biggest to the smallest by: absolute value of :attr:`StatisticDiff.size_diff`, :attr:`StatisticDiff.size`, absolute value of :attr:`StatisticDiff.count_diff`, :attr:`Statistic.count` and then by :attr:`StatisticDiff.traceback`.
.. method:: dump(filename) Write the snapshot into a file. Use :meth:`load` to reload the snapshot.
.. method:: filter_traces(filters)
Create a new :class:`Snapshot` instance with a filtered :attr:`traces`
sequence, *filters* is a list of :class:`DomainFilter` and
:class:`Filter` instances. If *filters* is an empty list, return a new
:class:`Snapshot` instance with a copy of the traces.
All inclusive filters are applied at once, a trace is ignored if no
inclusive filters match it. A trace is ignored if at least one exclusive
filter matches it.
.. versionchanged:: 3.6
:class:`DomainFilter` instances are now also accepted in *filters*.
.. classmethod:: load(filename) Load a snapshot from a file. See also :meth:`dump`.
.. method:: statistics(key_type: str, cumulative: bool=False) Get statistics as a sorted list of :class:`Statistic` instances grouped by *key_type*: ===================== ======================== key_type description ===================== ======================== ``'filename'`` filename ``'lineno'`` filename and line number ``'traceback'`` traceback ===================== ======================== If *cumulative* is ``True``, cumulate size and count of memory blocks of all frames of the traceback of a trace, not only the most recent frame. The cumulative mode can only be used with *key_type* equals to ``'filename'`` and ``'lineno'``. The result is sorted from the biggest to the smallest by: :attr:`Statistic.size`, :attr:`Statistic.count` and then by :attr:`Statistic.traceback`.
.. attribute:: traceback_limit Maximum number of frames stored in the traceback of :attr:`traces`: result of the :func:`get_traceback_limit` when the snapshot was taken.
.. attribute:: traces Traces of all memory blocks allocated by Python: sequence of :class:`Trace` instances. The sequence has an undefined order. Use the :meth:`Snapshot.statistics` method to get a sorted list of statistics.
Statistic on memory allocations.
:func:`Snapshot.statistics` returns a list of :class:`Statistic` instances.
See also the :class:`StatisticDiff` class.
.. attribute:: count Number of memory blocks (``int``).
.. attribute:: size Total size of memory blocks in bytes (``int``).
.. attribute:: traceback Traceback where the memory block was allocated, :class:`Traceback` instance.
Statistic difference on memory allocations between an old and a new :class:`Snapshot` instance.
:func:`Snapshot.compare_to` returns a list of :class:`StatisticDiff` instances. See also the :class:`Statistic` class.
.. attribute:: count Number of memory blocks in the new snapshot (``int``): ``0`` if the memory blocks have been released in the new snapshot.
.. attribute:: count_diff Difference of number of memory blocks between the old and the new snapshots (``int``): ``0`` if the memory blocks have been allocated in the new snapshot.
.. attribute:: size Total size of memory blocks in bytes in the new snapshot (``int``): ``0`` if the memory blocks have been released in the new snapshot.
.. attribute:: size_diff Difference of total size of memory blocks in bytes between the old and the new snapshots (``int``): ``0`` if the memory blocks have been allocated in the new snapshot.
.. attribute:: traceback Traceback where the memory blocks were allocated, :class:`Traceback` instance.
Trace of a memory block.
The :attr:`Snapshot.traces` attribute is a sequence of :class:`Trace` instances.
.. versionchanged:: 3.6 Added the :attr:`domain` attribute.
.. attribute:: domain Address space of a memory block (``int``). Read-only property. tracemalloc uses the domain ``0`` to trace memory allocations made by Python. C extensions can use other domains to trace other resources.
.. attribute:: size Size of the memory block in bytes (``int``).
.. attribute:: traceback Traceback where the memory block was allocated, :class:`Traceback` instance.
Sequence of :class:`Frame` instances sorted from the oldest frame to the most recent frame.
A traceback contains at least 1 frame. If the tracemalloc module
failed to get a frame, the filename "<unknown>" at line number 0 is
used.
When a snapshot is taken, tracebacks of traces are limited to :func:`get_traceback_limit` frames. See the :func:`take_snapshot` function. The original number of frames of the traceback is stored in the :attr:`Traceback.total_nframe` attribute. That allows to know if a traceback has been truncated by the traceback limit.
The :attr:`Trace.traceback` attribute is an instance of :class:`Traceback` instance.
.. versionchanged:: 3.7 Frames are now sorted from the oldest to the most recent, instead of most recent to oldest.
.. attribute:: total_nframe Total number of frames that composed the traceback before truncation. This attribute can be set to ``None`` if the information is not available.
.. versionchanged:: 3.9 The :attr:`Traceback.total_nframe` attribute was added.
.. method:: format(limit=None, most_recent_first=False)
Format the traceback as a list of lines. Use the :mod:`linecache` module to
retrieve lines from the source code. If *limit* is set, format the *limit*
most recent frames if *limit* is positive. Otherwise, format the
``abs(limit)`` oldest frames. If *most_recent_first* is ``True``, the order
of the formatted frames is reversed, returning the most recent frame first
instead of last.
Similar to the :func:`traceback.format_tb` function, except that
:meth:`.format` does not include newlines.
Example::
print("Traceback (most recent call first):")
for line in traceback:
print(line)
Output::
Traceback (most recent call first):
File "test.py", line 9
obj = Object()
File "test.py", line 12
tb = tracemalloc.get_object_traceback(f())