: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.
Examples
--------
Display the top 10
^^^^^^^^^^^^^^^^^^
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.
Compute differences
^^^^^^^^^^^^^^^^^^^
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.
Get the traceback of a memory block
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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.
Pretty top
^^^^^^^^^^
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.
Record the current and peak size of all traced memory blocks
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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(...))``).
API
---
Functions
^^^^^^^^^
.. 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.
DomainFilter
^^^^^^^^^^^^
.. class:: DomainFilter(inclusive: bool, domain: int)
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
^^^^^^
.. class:: Filter(inclusive: bool, filename_pattern: str, lineno: int=None, all_frames: bool=False, domain: int=None)
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` module
* ``Filter(False, tracemalloc.__file__)`` excludes traces of the
:mod:`tracemalloc` module
* ``Filter(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
^^^^^
.. class:: Frame
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
^^^^^^^^
.. class:: Snapshot
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
^^^^^^^^^
.. class:: Statistic
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.
StatisticDiff
^^^^^^^^^^^^^
.. class:: StatisticDiff
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
^^^^^
.. class:: Trace
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.
Traceback
^^^^^^^^^
.. class:: Traceback
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())