tracemalloc — Trace memory allocations¶
New in version 3.4.
Source code: 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 PYTHONTRACEMALLOC environment
variable to 1, or by using -X tracemalloc command line
option. The 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
PYTHONTRACEMALLOC environment variable to 25, or use the
-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 collections module allocated 244 KiB to build
namedtuple types.
See 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 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 Snapshot.dump() method to analyze the snapshot offline. Then use the
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 importlib module to
load data (bytecode and constants) from modules: 870.1 KiB. The traceback is
where the importlib loaded data most recently: on the import pdb
line of the 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 Snapshot.statistics() for more options.
API¶
Functions¶
- 
tracemalloc.get_object_traceback(obj)¶
- Get the traceback where the Python object obj was allocated. Return a - Tracebackinstance, or- Noneif the- tracemallocmodule is not tracing memory allocations or did not trace the allocation of the object.- See also - gc.get_referrers()and- sys.getsizeof()functions.
- 
tracemalloc.get_traceback_limit()¶
- Get the maximum number of frames stored in the traceback of a trace. - The - tracemallocmodule must be tracing memory allocations to get the limit, otherwise an exception is raised.- The limit is set by the - start()function.
- 
tracemalloc.get_traced_memory()¶
- Get the current size and peak size of memory blocks traced by the - tracemallocmodule as a tuple:- (current: int, peak: int).
- 
tracemalloc.get_tracemalloc_memory()¶
- Get the memory usage in bytes of the - tracemallocmodule used to store traces of memory blocks. Return an- int.
- 
tracemalloc.is_tracing()¶
- Trueif the- tracemallocmodule is tracing Python memory allocations,- Falseotherwise.
- 
tracemalloc.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.- Storing more than - 1frame is only useful to compute statistics grouped by- 'traceback'or to compute cumulative statistics: see the- Snapshot.compare_to()and- Snapshot.statistics()methods.- Storing more frames increases the memory and CPU overhead of the - tracemallocmodule. Use the- get_tracemalloc_memory()function to measure how much memory is used by the- tracemallocmodule.- The - PYTHONTRACEMALLOCenvironment variable (- PYTHONTRACEMALLOC=NFRAME) and the- -X- tracemalloc=NFRAMEcommand line option can be used to start tracing at startup.- See also - stop(),- is_tracing()and- get_traceback_limit()functions.
- 
tracemalloc.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 - take_snapshot()function to take a snapshot of traces before clearing them.- See also - start(),- is_tracing()and- clear_traces()functions.
- 
tracemalloc.take_snapshot()¶
- Take a snapshot of traces of memory blocks allocated by Python. Return a new - Snapshotinstance.- The snapshot does not include memory blocks allocated before the - tracemallocmodule started to trace memory allocations.- Tracebacks of traces are limited to - get_traceback_limit()frames. Use the nframe parameter of the- start()function to store more frames.- The - tracemallocmodule must be tracing memory allocations to take a snapshot, see the- start()function.- See also the - get_object_traceback()function.
DomainFilter¶
- 
class tracemalloc.DomainFilter(inclusive: bool, domain: int)¶
- Filter traces of memory blocks by their address space (domain). - New in version 3.6. - 
inclusive¶
- If inclusive is - True(include), match memory blocks allocated in the address space- domain.- If inclusive is - False(exclude), match memory blocks not allocated in the address space- domain.
 - 
domain¶
- Address space of a memory block ( - int). Read-only property.
 
- 
Filter¶
- 
class tracemalloc.Filter(inclusive: bool, filename_pattern: str, lineno: int=None, all_frames: bool=False, domain: int=None)¶
- Filter on traces of memory blocks. - See the - 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- subprocessmodule
- Filter(False, tracemalloc.__file__)excludes traces of the- tracemallocmodule
- Filter(False, "<unknown>")excludes empty tracebacks
 - Changed in version 3.5: The - '.pyo'file extension is no longer replaced with- '.py'.- Changed in version 3.6: Added the - domainattribute.- 
domain¶
- Address space of a memory block ( - intor- None).- tracemalloc uses the domain - 0to trace memory allocations made by Python. C extensions can use other domains to trace other resources.
 - 
inclusive¶
- If inclusive is - True(include), only match memory blocks allocated in a file with a name matching- filename_patternat line number- lineno.- If inclusive is - False(exclude), ignore memory blocks allocated in a file with a name matching- filename_patternat line number- lineno.
 - 
lineno¶
- Line number ( - int) of the filter. If lineno is- None, the filter matches any line number.
 - 
filename_pattern¶
- Filename pattern of the filter ( - str). Read-only property.
 - 
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- get_traceback_limit()function and- Snapshot.traceback_limitattribute.
 
Frame¶
Snapshot¶
- 
class tracemalloc.Snapshot¶
- Snapshot of traces of memory blocks allocated by Python. - The - take_snapshot()function creates a snapshot instance.- 
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 - StatisticDiffinstances grouped by key_type.- See the - Snapshot.statistics()method for key_type and cumulative parameters.- The result is sorted from the biggest to the smallest by: absolute value of - StatisticDiff.size_diff,- StatisticDiff.size, absolute value of- StatisticDiff.count_diff,- Statistic.countand then by- StatisticDiff.traceback.
 - 
filter_traces(filters)¶
- Create a new - Snapshotinstance with a filtered- tracessequence, filters is a list of- DomainFilterand- Filterinstances. If filters is an empty list, return a new- Snapshotinstance 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. - Changed in version 3.6: - DomainFilterinstances are now also accepted in filters.
 - 
statistics(key_type: str, cumulative: bool=False)¶
- Get statistics as a sorted list of - Statisticinstances 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: - Statistic.size,- Statistic.countand then by- Statistic.traceback.
 - 
traceback_limit¶
- Maximum number of frames stored in the traceback of - traces: result of the- get_traceback_limit()when the snapshot was taken.
 - 
traces¶
- Traces of all memory blocks allocated by Python: sequence of - Traceinstances.- The sequence has an undefined order. Use the - Snapshot.statistics()method to get a sorted list of statistics.
 
- 
Statistic¶
- 
class tracemalloc.Statistic¶
- Statistic on memory allocations. - Snapshot.statistics()returns a list of- Statisticinstances.- See also the - StatisticDiffclass.- 
count¶
- Number of memory blocks ( - int).
 - 
size¶
- Total size of memory blocks in bytes ( - int).
 
- 
StatisticDiff¶
- 
class tracemalloc.StatisticDiff¶
- Statistic difference on memory allocations between an old and a new - Snapshotinstance.- Snapshot.compare_to()returns a list of- StatisticDiffinstances. See also the- Statisticclass.- 
count¶
- Number of memory blocks in the new snapshot ( - int):- 0if the memory blocks have been released in the new snapshot.
 - 
count_diff¶
- Difference of number of memory blocks between the old and the new snapshots ( - int):- 0if the memory blocks have been allocated in the new snapshot.
 - 
size¶
- Total size of memory blocks in bytes in the new snapshot ( - int):- 0if the memory blocks have been released in the new snapshot.
 - 
size_diff¶
- Difference of total size of memory blocks in bytes between the old and the new snapshots ( - int):- 0if the memory blocks have been allocated in the new snapshot.
 
- 
Trace¶
- 
class tracemalloc.Trace¶
- Trace of a memory block. - The - Snapshot.tracesattribute is a sequence of- Traceinstances.- Changed in version 3.6: Added the - domainattribute.- 
domain¶
- Address space of a memory block ( - int). Read-only property.- tracemalloc uses the domain - 0to trace memory allocations made by Python. C extensions can use other domains to trace other resources.
 - 
size¶
- Size of the memory block in bytes ( - int).
 
- 
Traceback¶
- 
class tracemalloc.Traceback¶
- Sequence of - Frameinstances sorted from the oldest frame to the most recent frame.- A traceback contains at least - 1frame. If the- tracemallocmodule failed to get a frame, the filename- "<unknown>"at line number- 0is used.- When a snapshot is taken, tracebacks of traces are limited to - get_traceback_limit()frames. See the- take_snapshot()function.- The - Trace.tracebackattribute is an instance of- Tracebackinstance.- Changed in version 3.7: Frames are now sorted from the oldest to the most recent, instead of most recent to oldest. - 
format(limit=None, most_recent_first=False)¶
- Format the traceback as a list of lines with newlines. Use the - linecachemodule 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 - traceback.format_tb()function, except that- 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()) 
 
- 
