Add a command-line interface to tracemalloc #159560

Feature or enhancement

Proposal:

Today, to check memory allocations of a script with tracemalloc you have to modify the script itself: call tracemalloc.start(), take a snapshot at the right place, then print the statistics. For simple cases I think it would be convenient to run it the same way as cProfile, without touching the code:

python -m tracemalloc [-o OUTFILE] [-t {filename,lineno,traceback}] [--cumulative]
                      [-n NFRAME] [-l LIMIT] (-m module | script.py) [args ...]

Tracing starts right before the program runs. When it exits, a snapshot is taken and the top allocations that are still alive get printed, plus the total and the peak traced size:

$ python -m tracemalloc -l 5 script.py
Top 5 lineno allocations still alive at exit:
script.py:2: size=981 KiB, count=101, average=9942 B
<frozen runpy>:266: size=434 B, count=4, average=108 B
<frozen runpy>:102: size=400 B, count=1, average=400 B
<frozen runpy>:81: size=400 B, count=1, average=400 B
script.py:1: size=168 B, count=1, average=168 B
2 other: size=90 B, count=2
Total size: 982 KiB
Peak size: 983 KiB

Options:

• -o OUTFILE dumps the snapshot instead of printing it, so it can be loaded later with Snapshot.load() ( same idea as cProfile -o )
• -t key type for Snapshot.statistics(), lineno by default
• --cumulative cumulative mode of Snapshot.statistics()
• -n max number of frames, same as tracemalloc.start(nframe)
• -l number of statistics to display, 10 by default
• -m run a module, like python -m

The traced program gets the same sys.argv, __name__ and sys.path[0] as when it runs directly. Memory freed before exit only shows up in the peak size.

Has this already been discussed elsewhere?

I have already discussed this feature proposal on Discourse

Links to previous discussion of this feature:

https://discuss.python.org/t/run-tracemalloc-module-as-a-script/50821 ( Marc-André Lemburg suggested to submit a PR )

Linked PRs

• gh-159560: Add a command-line interface to tracemalloc #159563