27.7. 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.
27.7.1. Examples¶
27.7.1.1. 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 4.8 MiB
data (bytecode and constants) from
modules and that the collections module allocated 244 KiB
to build
namedtuple types.
See Snapshot.statistics() for more options.
27.7.1.2. 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 8.2 MiB
of module data (bytecode and
constants), and that this is 4.4 MiB
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.
27.7.1.3. 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 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.
27.7.1.4. 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, group_by='lineno', limit=10): snapshot = snapshot.filter_traces(( tracemalloc.Filter(False, "<frozen importlib._bootstrap>"), tracemalloc.Filter(False, "<unknown>"), )) top_stats = snapshot.statistics(group_by) print("Top %s lines" % limit) for index, stat in enumerate(top_stats[:limit], 1): frame = stat.traceback[0] # replace "/path/to/module/file.py" with "module/file.py" filename = os.sep.join(frame.filename.split(os.sep)[-2:]) print("#%s: %s:%s: %.1f KiB" % (index, 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.
27.7.2. API¶
27.7.2.1. Functions¶
-
tracemalloc.
get_object_traceback
(obj)¶ Get the traceback where the Python object obj was allocated. Return a Traceback instance, or
None
if the tracemalloc module 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 tracemalloc module 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 tracemalloc module as a tuple:
(current: int, peak: int)
.
-
tracemalloc.
get_tracemalloc_memory
()¶ Get the memory usage in bytes of the tracemalloc module used to store traces of memory blocks. Return an int.
-
tracemalloc.
is_tracing
()¶ True
if the tracemalloc module is tracing Python memory allocations,False
otherwise.
-
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 to1
.Storing more than
1
frame 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 tracemalloc module. Use the get_tracemalloc_memory() function to measure how much memory is used by the tracemalloc module.
The PYTHONTRACEMALLOC environment variable (
PYTHONTRACEMALLOC=NFRAME
) and the -Xtracemalloc=NFRAME
command 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 Snapshot instance.
The snapshot does not include memory blocks allocated before the tracemalloc module 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 tracemalloc module must be tracing memory allocations to take a snapshot, see the start() function.
See also the get_object_traceback() function.
27.7.2.2. 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.
-
27.7.2.3. 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 subprocess moduleFilter(False, tracemalloc.__file__)
excludes traces of the tracemalloc moduleFilter(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 domain attribute.
-
domain
¶ Address space of a memory block (
int
orNone
).
-
inclusive
¶ If inclusive is
True
(include), only match memory blocks allocated in a file with a name matching filename_pattern at line number lineno.If inclusive is
False
(exclude), ignore memory blocks allocated in a file with a name matching filename_pattern at line number lineno.
-
lineno
¶ Line number (
int
) of the filter. If lineno isNone
, 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 isFalse
, 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_limit attribute.
27.7.2.4. Frame¶
27.7.2.5. 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, group_by: str, cumulative: bool=False)¶ Compute the differences with an old snapshot. Get statistics as a sorted list of StatisticDiff instances grouped by group_by.
See the Snapshot.statistics() method for group_by 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.count and then by StatisticDiff.traceback.
-
filter_traces
(filters)¶ Create a new Snapshot instance with a filtered traces sequence, filters is a list of DomainFilter and Filter instances. If filters is an empty list, return a new 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.
Changed in version 3.6: DomainFilter instances are now also accepted in filters.
-
statistics
(group_by: str, cumulative: bool=False)¶ Get statistics as a sorted list of Statistic instances grouped by group_by:
group_by 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 group_by equals to‘filename’
and‘lineno’
.The result is sorted from the biggest to the smallest by: Statistic.size, Statistic.count and 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 Trace instances.
The sequence has an undefined order. Use the Snapshot.statistics() method to get a sorted list of statistics.
-
27.7.2.6. Statistic¶
-
class
tracemalloc.
Statistic
¶ Statistic on memory allocations.
Snapshot.statistics() returns a list of Statistic instances.
See also the StatisticDiff class.
-
count
¶ Number of memory blocks (
int
).
-
size
¶ Total size of memory blocks in bytes (
int
).
-
27.7.2.7. StatisticDiff¶
-
class
tracemalloc.
StatisticDiff
¶ Statistic difference on memory allocations between an old and a new Snapshot instance.
Snapshot.compare_to() returns a list of StatisticDiff instances. See also the Statistic class.
-
count
¶ Number of memory blocks in the new snapshot (
int
):0
if 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
):0
if the memory blocks have been allocated in the new snapshot.
-
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.
-
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.
-
27.7.2.8. Trace¶
27.7.2.9. Traceback¶
-
class
tracemalloc.
Traceback
¶ Sequence of Frame instances sorted from the most recent frame to the oldest frame.
A traceback contains at least
1
frame. If thetracemalloc
module failed to get a frame, the filename“<unknown>”
at line number0
is used.When a snapshot is taken, tracebacks of traces are limited to get_traceback_limit() frames. See the take_snapshot() function.
The Trace.traceback attribute is an instance of Traceback instance.
-
format
(limit=None)¶ Format the traceback as a list of lines with newlines. Use the linecache module to retrieve lines from the source code. If limit is set, only format the limit most recent frames.
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())
-