This project is no longer maintained here, instead, for Python < 3.4, please see '', maintained by Victor Stinner.
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IMPORTANT! please read:

"pytracemalloc" is no longer maintained here.

As a consequence, this repository is now frozen, and we are no longer accepting new issues or changes to it. Instead, please see for the official implementation.

This repo and below information are kept here as an archive.


Debug tool tracking Python memory allocations. Provide the following information:

  • Allocated size and number of allocations per file, or optionally per file and line number
  • Compute the average size of memory allocations
  • Compute delta between two "snapshots"
  • Source of a memory allocation: filename and line number

Example (compact):

2013-02-28 23:40:18: Top 5 allocations per file
#1: .../Lib/test/ 3998 KB
#2: .../Lib/unittest/ 2343 KB
#3: .../ctypes/test/ 513 KB
#4: .../Lib/encodings/ 525 KB
#5: .../Lib/compiler/ 438 KB
other: 32119 KB
Total allocated size: 39939 KB

Another example (full):

2013-03-04 01:01:55: Top 10 allocations per file and line
#1: .../2.7/Lib/ size=408 KiB (+408 KiB), count=5379 (+5379), average=77 B
#2: .../unittest/test/ size=401 KiB (+401 KiB), count=6668 (+6668), average=61 B
#3: .../2.7/Lib/ size=319 KiB (+319 KiB), count=197 (+197), average=1 KiB
#4: .../Lib/test/ size=429 KiB (+301 KiB), count=5806 (+3633), average=75 B
#5: .../Lib/unittest/ size=162 KiB (+136 KiB), count=452 (+380), average=367 B
#6: .../Lib/test/ size=105 KiB (+105 KiB), count=1125 (+1125), average=96 B
#7: .../Lib/unittest/ size=77 KiB (+77 KiB), count=1149 (+1149), average=69 B
#8: .../Lib/test/ size=75 KiB (+75 KiB), count=1644 (+1644), average=46 B
#9: .../2.7/Lib/ size=64 KiB (+64 KiB), count=1000 (+1000), average=66 B
#10: .../Lib/test/ size=56 KiB (+56 KiB), count=932 (+932), average=61 B
3023 more: size=1580 KiB (+1138 KiB), count=12635 (+7801), average=128 B
Total: size=3682 KiB (+3086 KiB), count=36987 (+29908), average=101 B

Python module developed by Wyplay:

Project homepage:

Usage: Display top 25

Display the 25 files allocating the most memory every minute:

import tracemalloc
top = tracemalloc.DisplayTop(25)
# ... run your application ...

By default, the top 25 is written into sys.stdout. You can write the output into a file (here opened in append mode):

import tracemalloc
log = open("tracemalloc.log", "a")
top = tracemalloc.DisplayTop(25, file=log)
# ... run your application ...

Usage: Take snapshots

For deeper analysis, it's possible to take a snapshot every minute:

import tracemalloc
take_snapshot = tracemalloc.TakeSnapshot()
# take_snapshot.filename_template = "/tmp/trace-$pid-$timestamp.pickle"
# ... run your application ...

By default, files called "tracemalloc-XXXX.pickle" are created in the current directory. Uncomment and edit the "filename_template" line in the example to customize the filename. The filename template can use the following variables: $pid, $timestamp, $counter.

To display and compare snapshots, use the following command:

python -m tracemalloc trace1.pickle [trace2.pickle trace3.pickle ...]

Useful options:

  • --line-number (-l): use also the line number to group Python memory allocations
  • --first: compare with the first trace, instead of with the previous trace
  • --include=MATCH: Only include filenames matching pattern MATCH, the option can be specified multiple times
  • --exclude=MATCH: Exclude filenames matching pattern MATCH, the option can be specified multiple times

Display the help to see more options to customize the display, type:

python -m tracemalloc --help

It is also possible to take a snapshot explicitly:

snapshot = tracemalloc.Snapshot.create()

PYTRACEMALLOC environment variable

Set PYTRACEMALLOC environment variable to 1 to trace memory allocations at Python startup (call tracemalloc.enable()): "tracemalloc enabled" message should be written to the standard error stream (stderr).


$ PYTRACEMALLOC=1 python3.4 -q
tracemalloc enabled
>>> import tracemalloc
>>> tracemalloc.DisplayTop(5).display()
2013-06-01 18:51:48: Top 5 allocations per file
#1: <frozen importlib._bootstrap>: size=1267 KiB, count=10277, average=126 B
#2: .../Lib/collections/ size=119 KiB, count=636, average=192 B
#3: .../default/Lib/ size=98 KiB, count=751, average=133 B
#4: .../default/Lib/ size=91 KiB, count=443, average=212 B
#5: .../default/Lib/ size=58 KiB, count=53, average=1134 B
27 more: size=310 KiB, count=1469, average=216 B
Total Python memory: size=1945 KiB, count=13629, average=146 B
Total process memory: size=10 MiB (ignore tracemalloc: 23 KiB)


Patch Python

To install pytracemalloc, you need a modified Python runtime:

  • Download Python source code
  • Apply a patch (see below): patch -p1 < pythonXXX.patch
  • Compile and install Python: ./configure && make && sudo make install
  • It can be installed in a custom directory. For example: ./configure --prefix=/opt/mypython

There are 3 types of Python patch to use pytracemalloc:

  • Track free lists: track all Python objects. It is the recommended option.
    • Python 2.5.2: python2.5.2_track_free_list.patch
    • Python 2.7: python2.7_track_free_list.patch
    • Python 3.4: python3.4_track_free_list.patch
  • Don't track free lists: less accurate, but faster.
    • Python 2.5.6: python2.5.6.patch
    • Python 2.7: python2.7.patch
    • Python 3.4: python3.4.patch
  • Disable free lists: track all Python objects, slower.
    • Python 2.5: python2.5_no_free_list.patch
    • Python 2.7: python2.7_no_free_list.patch

Python uses "free lists" to avoid memory allocations for best performances. When an object is destroyed, the memory is not freed, but kept in a list. Creation of an object will try to reuse a dead object from the free list. A free list is specific to an object type, or sometimes also to the length of the object (for lists for example).

Python 3 uses free lists for the following object types:

  • float
  • tuple, list, set, dict
  • bound method, C function, frame

Python 2 uses free lists for the following object types:

  • int, float, unicode
  • tuple, list, set, dict
  • bound method, C function, frame

Compile and install pytracemalloc


  • Python 2.5 - 3.4
  • glib version 2
  • (optional) psutil to get the process memory. pytracemalloc is able to read the memory usage of the process on Linux without psutil.


/opt/mypython/bin/python install


Call tracemalloc.enable() as early as possible to get the most complete statistics. Otherwise, some Python memory allocations made by your application will be ignored by tracemalloc. Set PYTRACEMALLOC environment variable to 1 to enable tracing at Python startup.

Call tracemalloc.disable() to stop tracing memory allocations. It is automatically called at exit using the atexit module.

The version of the module is tracemalloc.__version__ (string, ex: "0.9.1").


  • enable()

    Start tracing Python memory allocations.

  • disable()

    Stop tracing Python memory allocations and stop the timer started by start_timer().

  • get_process_memory()

    Get the memory usage of the current process in bytes. Return None if the platform is not supported.

    Use the psutil module if available.

    New in pytracemalloc 0.8.

  • start_timer(delay: int, func: callable, args: tuple=(), kwargs: dict={})

    Start a timer calling func(*args, **kwargs) every delay seconds.

    The timer is based on the Python memory allocator, it is not real time. func is called after at least delay seconds, it is not called exactly after delay seconds if no Python memory allocation occurred.

    If start_timer() is called twice, previous parameters are replaced. The timer has a resolution of 1 second.

    start_timer() is used by DisplayTop and TakeSnapshot to run regulary a task.

  • stop_timer()

    Stop the timer started by start_timer().


  • DisplayGarbage(file=sys.stdout): Display new objects added to gc.garbage. By default, it displays uncollectable objects, see the documentation of gc.garbage. Use gc.set_debug(gc.DEBUG_SAVEALL) to display all deleted objects. Methods:

    • display(): display new objects added to gc.garbage since last call


    • color (bool, default: stream.isatty()): if True, use colors
    • cumulative (bool, default: False): if True, display() displays all objects, if False, display() only displays new objects added to gc.garbage.
    • format_object (callable, default: repr.repr): function formatting an object
  • DisplayTop(count: int, file=sys.stdout): Display the list of the N biggest memory allocations. Methods:

    • display(): display the top
    • start(delay: int): start a task using tracemalloc timer to display the top every delay seconds
    • stop(): stop the task started by the start() method


    • color (bool, default: stream.isatty()): if True, use colors
    • compare_with_previous (bool, default: True): if True, compare with the previous top, otherwise compare with the first one
    • filename_parts (int, default: 3): Number of displayed filename parts
    • show_average (bool, default: True): if True, show the average size of allocations
    • show_count (bool, default: True): if True, show the number of allocations
    • show_lineno (bool, default: False): if True, use also the line number, not only the filename
    • show_size (bool, default: True): if True, show the size of allocations
    • user_data_callback (callable, default: None): optional callback collecting user data. See Snapshot.create().
  • Snapshot: Snapshot of Python memory allocations. Use TakeSnapshot to regulary take snapshots. Methods:

    • create(user_data_callback=None): take a snapshot. If user_data_callback is specified, it must be a callable object returning a list of (title: str, format: str, value: int). format must be "size". The list must always have the same length and the same order to be able to compute differences between values. Example: [('Video memory', 'size', 234902)].
    • filter_filenames(patterns: str|list, include: bool): remove filenames not matching any pattern if include is True, or remove filenames matching a pattern if include is False (exclude). See fnmatch.fnmatch() for the syntax of patterns.
    • write(filename): write the snapshot into a file


    • pid (int): identifier of the process which created the snapshot
    • stats (dict): raw memory allocation statistics
    • timestamp (str): date and time of the creation of the snapshot
  • TakeSnapshot: Task taking snapshots of Python memory allocations: write them into files. Methods:

    • start(delay: int): start a task taking a snapshot every delay seconds
    • stop(): stop the task started by the start() method
    • take_snapshot(): take a snapshot


    • filename_template (str): template to create a filename. "Variables" can be used in the template: "$pid" (identifier of the current process), "$timestamp" (current date and time) and "$counter" (counter starting at 1 and incremented at each snapshot).
    • user_data_callback (callable, default: None): optional callback collecting user data. See Snapshot.create().


Version 0.9.1 (2013-06-01)

  • Add PYTRACEMALLOC environment variable to trace memory allocation as early as possible at Python startup
  • Disable the timer while calling its callback to not call the callback while it is running
  • Fix pythonXXX_track_free_list.patch patches for zombie frames
  • Use also MiB, GiB and TiB units to format a size, not only B and KiB

Version 0.9 (2013-05-31)

  • Tracking free lists is now the recommended method to patch Python
  • Fix code tracking Python free lists and python2.7_track_free_list.patch
  • Add patches tracking free lists for Python 2.5.2 and 3.4.

Version 0.8.1 (2013-03-23)

  • Fix python2.7.patch and python3.4.patch when Python is not compiled in debug mode (without --with-pydebug)
  • Fix DisplayTop: display "0 B" instead of an empty string if the size is zero (ex: trace in user data)
  • automatically detects which patch was applied on Python

Version 0.8 (2013-03-19)

  • The top uses colors and displays also the memory usage of the process
  • Add DisplayGarbage class
  • Add get_process_memory() function
  • Support collecting arbitrary user data using a callback: Snapshot.create(), DisplayTop() and TakeSnapshot() have has an optional user_data_callback parameter/attribute
  • Display the name of the previous snapshot when comparing two snapshots
  • Command line (-m tracemalloc):
    • Add --color and --no-color options
    • --include and --exclude command line options can now be specified multiple times
  • Automatically disable tracemalloc at exit
  • Remove get_source() and get_stats() functions: they are now private

Version 0.7 (2013-03-04)

  • First public version

See also