Functions

clear_traces() function:

Clear traces of memory blocks allocated by Python.

See also stop().

get_object_traceback(obj) function:

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.

get_traceback_limit() function:

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.

get_traced_memory() function:

Get the current size and maximum size of memory blocks traced by the tracemalloc module as a tuple: (size: int, max_size: int).

get_tracemalloc_memory() function:

Get the memory usage in bytes of the tracemalloc module used to store traces of memory blocks. Return an int.

is_tracing() function:

True if the tracemalloc module is tracing Python memory allocations, False otherwise.

See also start() and stop() functions.

start(nframe: int=1) function:

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 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 -X tracemalloc=NFRAME command line option can be used to start tracing at startup.

See also stop(), is_tracing() and get_traceback_limit() functions.

stop() function:

Stop tracing Python memory allocations: uninstall hooks on Python memory allocators. Clear also traces of memory blocks allocated by Python

Call take_snapshot() function to take a snapshot of traces before clearing them.

See also start() and is_tracing() functions.

take_snapshot() function:

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.

Filter

Filter(inclusive: bool, filename_pattern: str, lineno: int=None, all_frames: bool=False) class:

Filter on traces of memory blocks.

See the fnmatch.fnmatch() function for the syntax of filename_pattern. The '.pyc' and '.pyo' file extensions are replaced with '.py'.

Examples:

• Filter(True, subprocess.__file__) only includes traces of the subprocess module
• Filter(False, tracemalloc.__file__) excludes traces of the tracemalloc module
• Filter(False, "<unknown>") excludes empty tracebacks

inclusive attribute:

If inclusive is True (include), only trace 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 attribute:

Line number (int) of the filter. If lineno is None, the filter matches any line number.

filename_pattern attribute:

Filename pattern of the filter (str).

all_frames attribute:

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 is ignored if the traceback limit is less than 2. See the get_traceback_limit() function and Snapshot.traceback_limit attribute.

Frame

Frame class:

Frame of a traceback.

The Traceback class is a sequence of Frame instances.

filename attribute:

Filename (str).

lineno attribute:

Line number (int).

Snapshot

Snapshot class:

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) method:

Compute the differences with an old snapshot. Get statistics as a sorted list of StatisticDiff instances grouped by group_by.

See the 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.

dump(filename) method:

Write the snapshot into a file.

Use load() to reload the snapshot.

filter_traces(filters) method:

Create a new Snapshot instance with a filtered traces sequence, filters is a list of 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 matchs it.

load(filename) classmethod:

Load a snapshot from a file.

See also dump().

statistics(group_by: str, cumulative: bool=False) method:

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' and traceback_limit greater than 1.

The result is sorted from the biggest to the smallest by: Statistic.size, Statistic.count and then by Statistic.traceback.

traceback_limit attribute:

Maximum number of frames stored in the traceback of traces: result of the get_traceback_limit() when the snapshot was taken.

traces attribute:

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.

Statistic

Statistic class:

Statistic on memory allocations.

Snapshot.statistics() returns a list of Statistic instances.

See also the StatisticDiff class.

count attribute:

Number of memory blocks (int).

size attribute:

Total size of memory blocks in bytes (int).

traceback attribute:

Traceback where the memory block was allocated, Traceback instance.

StatisticDiff

StatisticDiff class:

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 attribute:

Number of memory blocks in the new snapshot (int): 0 if the memory blocks have been released in the new snapshot.

count_diff attribute:

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 attribute:

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 attribute:

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.

traceback attribute:

Traceback where the memory blocks were allocated, Traceback instance.

Trace

Trace class:

Trace of a memory block.

The Snapshot.traces attribute is a sequence of Trace instances.

size attribute:

Size of the memory block in bytes (int).

traceback attribute:

Traceback where the memory block was allocated, Traceback instance.

Traceback

Traceback class:

Sequence of Frame instances sorted from the most recent frame to the oldest 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 get_traceback_limit() frames. See the take_snapshot() function.

The Trace.traceback attribute is an instance of Traceback instance.

Log calls to the memory allocator

A different approach is to log calls to malloc(), realloc() and free() functions. Calls can be logged into a file or send to another computer through the network. Example of a log entry: name of the function, size of the memory block, address of the memory block, Python traceback where the allocation occurred, timestamp.

Logs cannot be used directly, getting the current status of the memory requires to parse previous logs. For example, it is not possible to get directly the traceback of a Python object, like get_object_traceback(obj) does with traces.

Python uses objects with a very short lifetime and so makes an extensive use of memory allocators. It has an allocator optimized for small objects (less than 512 bytes) with a short lifetime. For example, the Python test suites calls malloc(), realloc() or free() 270,000 times per second in average. If the size of log entry is 32 bytes, logging produces 8.2 MB per second or 29.0 GB per hour.

The alternative was rejected because it is less efficient and has less features. Parsing logs in a different process or a different computer is slower than maintaining traces on allocated memory blocks in the same process.