pyinstrument

Pyinstrument is a Python profiler. A profiler is a tool to help you 'optimize' your code - make it faster. It sounds obvious, but to get the biggest speed increase you must focus on the slowest part of your program. Pyinstrument helps you find it!

Documentation

• Installation
• How to use it
  • Command-line
  • Python
  • Django
• How does it work?
• Changelog
• Further information
  • Call stack profiling?

Installation

pip install pyinstrument

Pyinstrument supports Python 2.7 and 3.3+.

How to use it

Pyinstrument tells you which sections of code are making your software slow. It does this by observing your program's execution and then presenting a report that highlights the slow parts.

I want to profile a Python script

You can call Pyinstrument directly from the command line. Instead of writing python script.py, type pyinstrument script.py. Your script will run as normal, and at the end (or when you press ^C), Pyinstrument will output a nice colored summary of where most of the time was spent.

Here are the options you can use:

python -m pyinstrument [options] myscript.py [args...]

Options:
  -h, --help            show this help message and exit
  --html                output HTML instead of text
  -o OUTFILE, --outfile=OUTFILE
                        save report to <outfile>
  --unicode             force unicode text output
  --no-unicode          force ascii text output
  --color               force ansi color text output
  --no-color            force no color text output

I want to profile a specific chunk of code

Pyinstrument also has a Python API. Just surround your code with Pyinstrument, like this:

from pyinstrument import Profiler

profiler = Profiler()
profiler.start()

# code you want to profile

profiler.stop()

print(profiler.output_text(unicode=True, color=True))

(You can omit the unicode and color flags if your output/terminal does not support them.)

I want to profile a slow web request in Django

Pyinstrument can also profile web requests in Django. To use it, add pyinstrument.middleware.ProfilerMiddleware to MIDDLEWARE_CLASSES in your settings.py.

Once installed, add ?profile to the end of a request URL to activate the profiler. Your request will run as normal, but instead of getting the response, you'll get pyinstrument's analysis of the request in a web page.

If you're writing an API, it's not easy to change the URL when you want to profile something. In this case, add PYINSTRUMENT_PROFILE_DIR = 'profiles' to your settings.py. Pyinstrument will profile every request and save the HTML output to the folder profiles in your working directory.

How is it different to profile or cProfile?

Statistical profiling (not tracing)

Pyinstrument is a statistical profiler. That means it does not track every single function call that your program makes. Instead, it's 'sampling' the process every 1ms and recording the call stack at that point.

That gives some clear advantages over other profilers. Statistical profilers are much lower-overhead (and thus accurate) than tracing profilers.

	Django template render × 4000	Overhead
Base	████████████████ 0.33s
pyinstrument	████████████████████ 0.43s	30%
cProfile	█████████████████████████████ 0.61s	84%
profile	██████████████████████████████████...██ 6.79s	2057%

This overhead is important a lot can distort your timings. When using a tracing profiler, code that makes a lot of Python function calls could appear to take longer than code that does not.

Full-stack recording

The standard Python profilers profile and cProfile produce output where time is totalled according to the time spent in each function. This is great, but it falls down when you profile code where most time is spent in framework code that you're not familiar with.

Here's an example of profile output when using Django.

151940 function calls (147672 primitive calls) in 1.696 seconds

   Ordered by: cumulative time

   ncalls  tottime  percall  cumtime  percall filename:lineno(function)
        1    0.000    0.000    1.696    1.696 profile:0(<code object <module> at 0x1053d6a30, file "./manage.py", line 2>)
        1    0.001    0.001    1.693    1.693 manage.py:2(<module>)
        1    0.000    0.000    1.586    1.586 __init__.py:394(execute_from_command_line)
        1    0.000    0.000    1.586    1.586 __init__.py:350(execute)
        1    0.000    0.000    1.142    1.142 __init__.py:254(fetch_command)
       43    0.013    0.000    1.124    0.026 __init__.py:1(<module>)
      388    0.008    0.000    1.062    0.003 re.py:226(_compile)
      158    0.005    0.000    1.048    0.007 sre_compile.py:496(compile)
        1    0.001    0.001    1.042    1.042 __init__.py:78(get_commands)
      153    0.001    0.000    1.036    0.007 re.py:188(compile)
  106/102    0.001    0.000    1.030    0.010 __init__.py:52(__getattr__)
        1    0.000    0.000    1.029    1.029 __init__.py:31(_setup)
        1    0.000    0.000    1.021    1.021 __init__.py:57(_configure_logging)
        2    0.002    0.001    1.011    0.505 log.py:1(<module>)

It's often hard to understand how your own code relates to these traces.

Pyinstrument records the entire stack, so tracking expensive calls is much easier.

'Wall-clock' time (not CPU time)

Pyinstrument records duration using 'wall-clock' time. That means that when you're writing a program that downloads data, reads files, and talks to databases, that time is included in the tracked time by pyinstrument.

That's really important when debugging performance problems, since Python is often used as a 'glue' language between other services. The problem might not be in your program, but you should still be able to find why it's slow.

How does it work?

Pyinstrument interrupts the program every 1ms and records the entire stack at that point. It does this using a C extension and PyEval_SetProfile, but only taking readings every 1ms. Check out this blog post for more info.

Changelog

What's new in v2.0.0

• Pyinstrument refactored to use a new profiling mode. Rather than using signals, pyintrument uses a new statistical profiler built on PyEval_SetProfile. This means no more main thread restriction, no more IO errors when using Pyinstrument, and no more 'setprofile' mode!

• Renderers. Users can customize Pyinstrument to use alternative renderers with the renderer argument on Profiler.output(), or using the --renderer argument on the command line.

• Recorders. To support other use cases of Pyinstrument (e.g. flame charts), pyinstrument now has a 'timeline' recorder mode. This mode records captured frames in a linear way, so the program execution can be viewed on a timeline.

What's new in v0.13

• pyinstrument command. You can now profile python scripts from the shell by running $ pyinstrument script.py. This is now equivalent to python -m pyinstrument. Thanks @asmeurer!

What's new in v0.12

• Application code is highlighted in HTML traces to make it easier to spot

• Added PYINSTRUMENT_PROFILE_DIR option to the Django interface, which will log profiles of all requests to a file the specified folder. Useful for profiling API calls.

• Added PYINSTRUMENT_USE_SIGNAL option to the Django interface, for use when signal mode presents problems.