API Reference

Command line interface

pyinstrument works just like python, on the command line, so you can call your scripts like pyinstrument script.py or pyinstrument -m my_module.

When your script ends, or when you kill it with ctrl-c, pyinstrument will print a profile report to the console.

Usage: pyinstrument [options] scriptfile [arg] ...

  --version             show program's version number and exit
  -h, --help            show this help message and exit
  --load=FILENAME       instead of running a script, load a profile session
                        from a pyisession file
                        instead of running a script, load a previous profile
                        session as specified by an identifier
  -m MODULE_NAME        run library module as a script, like 'python -m
  --from-path           (POSIX only) instead of the working directory, look
                        for scriptfile in the PATH environment variable
  -o OUTFILE, --outfile=OUTFILE
                        save to <outfile>
  -r RENDERER, --renderer=RENDERER
                        how the report should be rendered. One of: 'text',
                        'html', 'json', 'speedscope' or python import path to
                        a renderer class. Defaults to the appropriate format
                        for the extension if OUTFILE is given, otherwise,
                        defaults to 'text'.
  -p RENDER_OPTION, --render-option=RENDER_OPTION
                        options to pass to the renderer, in the format
                        'flag_name' or 'option_name=option_value'. For
                        example, to set the option 'time', pass '-p
                        time=percent_of_total'. To pass multiple options, use
                        the -p option multiple times. You can set processor
                        options using dot-syntax, like '-p
                        processor_options.filter_threshold=0'. option_value is
                        parsed as a JSON value or a string.
  -t, --timeline        render as a timeline - preserve ordering and don't
                        condense repeated calls
  --hide=EXPR           glob-style pattern matching the file paths whose
                        frames to hide. Defaults to hiding non-application
  --hide-regex=REGEX    regex matching the file paths whose frames to hide.
                        Useful if --hide doesn't give enough control.
  --show=EXPR           glob-style pattern matching the file paths whose
                        frames to show, regardless of --hide or --hide-regex.
                        For example, use --show '*/<library>/*' to show frames
                        within a library that would otherwise be hidden.
  --show-regex=REGEX    regex matching the file paths whose frames to always
                        show. Useful if --show doesn't give enough control.
  --show-all            show everything
  --unicode             (text renderer only) force unicode text output
  --no-unicode          (text renderer only) force ascii text output
  --color               (text renderer only) force ansi color text output
  --no-color            (text renderer only) force no color text output

Python API

The Python API is also available, for calling pyinstrument directly from Python and writing integrations with with other tools.

The Profiler object

class pyinstrument.Profiler(interval=0.001, async_mode='enabled')

The profiler - this is the main way to use pyinstrument.

Note the profiling will not start until start() is called.

property interval: float

The minimum time, in seconds, between each stack sample. This translates into the resolution of the sampling.

property async_mode: str

Configures how this Profiler tracks time in a program that uses async/await.


When this profiler sees an await, time is logged in the function that awaited, rather than observing other coroutines or the event loop.


This profiler doesn’t attempt to track await. In a program that uses async/await, this will interleave other coroutines and event loop machinery in the profile. Use this option if async support is causing issues in your use case, or if you want to run multiple profilers at once.


Instructs the profiler to only profile the current async context. Frames that are observed in an other context are ignored, tracked instead as <out-of-context>.

property last_session: Session | None

The previous session recorded by the Profiler.


Instructs the profiler to start - to begin observing the program’s execution and recording frames.

The normal way to invoke start() is with a new instance, but you can restart a Profiler that was previously running, too. The sessions are combined.


caller_frame (types.FrameType | None) –

Set this to override the default behaviour of treating the caller of start() as the ‘start_call_stack’ - the instigator of the profile. Most renderers will trim the ‘root’ from the call stack up to this frame, to present a simpler output.

You might want to set this to inspect.currentframe().f_back if you are writing a library that wraps pyinstrument.


Stops the profiler observing, and sets last_session to the captured session.


The captured session.

Return type


property is_running

Returns True if this profiler is running - i.e. observing the program execution.


Resets the Profiler, clearing the last_session.


Context manager support.

Profilers can be used in with blocks! See this example:

with Profiler() as p:
    # your code here...

# profiling has ended. let's print the output.
print(file=sys.stdout, *, unicode=None, color=None, show_all=False, timeline=False)

Print the captured profile to the console.

  • file (IO[str]) – the IO stream to write to. Could be a file descriptor or sys.stdout, sys.stderr. Defaults to sys.stdout.

  • unicode (bool | None) – Override unicode support detection.

  • color (bool | None) – Override ANSI color support detection.

  • show_all (bool) – Sets the show_all parameter on the renderer.

  • timeline (bool) – Sets the timeline parameter on the renderer.

output_text(unicode=False, color=False, show_all=False, timeline=False)

Return the profile output as text, as rendered by ConsoleRenderer


Return the profile output as HTML, as rendered by HTMLRenderer


Opens the last profile session in your web browser.


Returns the last profile session, as rendered by renderer.


renderer (pyinstrument.renderers.base.Renderer) – The renderer to use.


class pyinstrument.session.Session

Represents a profile session, contains the data collected during a profile session.

static load(filename)

Load a previously saved session from disk.


filename (Union[str, os.PathLike[str]]) – The path to load from.

Return type



Saves a Session object to disk, in a JSON format.


filename (Union[str, os.PathLike[str]]) – The path to save to. Using the .pyisession extension is recommended.

static combine(session1, session2)

Combines two Session objects.

Sessions that are joined in this way probably shouldn’t be interpreted as timelines, because the samples are simply concatenated. But aggregate views (the default) of this data will work.

Return type



Parses the internal frame records and returns a tree of Frame objects. This object can be renderered using a Renderer object.

Return type

A Frame object, or None if the session is empty.


Renderers transform a tree of Frame objects into some form of output.

Rendering has two steps:

  1. First, the renderer will ‘preprocess’ the Frame tree, applying each processor in the processor property, in turn.

  2. The resulting tree is renderered into the desired format.

Therefore, rendering can be customised by changing the processors property. For example, you can disable time-aggregation (making the profile into a timeline) by removing aggregate_repeated_calls().

class pyinstrument.renderers.FrameRenderer(show_all=False, timeline=False, processor_options=None)

An abstract base class for renderers that process Frame objects using processor functions. Provides a common interface to manipulate the processors before rendering.

  • show_all (bool) – Don’t hide library frames - show everything that pyinstrument captures.

  • timeline (bool) – Instead of aggregating time, leave the samples in chronological order.

  • processor_options (dict[str, Any] | None) – A dictionary of processor options.

processors: ProcessorList

Processors installed on this renderer. This property is defined on the base class to provide a common way for users to add and manipulate them before calling render().

processor_options: dict[str, Any]

Dictionary containing processor options, passed to each processor.


Return a list of processors that this renderer uses by default.


Return a string that contains the rendered form of frame.

class pyinstrument.renderers.ConsoleRenderer(unicode=False, color=False, time='seconds', **kwargs)

Produces text-based output, suitable for text files or ANSI-compatible consoles.

  • unicode (bool) – Use unicode, like box-drawing characters in the output.

  • color (bool) – Enable color support, using ANSI color sequences.

  • time (str) – How to display the duration of each frame - 'seconds' or 'percent_of_total'

class pyinstrument.renderers.HTMLRenderer(**kwargs)

Renders a rich, interactive web page, as a string of HTML.

  • show_all – Don’t hide library frames - show everything that pyinstrument captures.

  • timeline – Instead of aggregating time, leave the samples in chronological order.

  • processor_options – A dictionary of processor options.

class pyinstrument.renderers.JSONRenderer(**kwargs)

Outputs a tree of JSON, containing processed frames.

  • show_all – Don’t hide library frames - show everything that pyinstrument captures.

  • timeline – Instead of aggregating time, leave the samples in chronological order.

  • processor_options – A dictionary of processor options.

class pyinstrument.renderers.SpeedscopeRenderer(**kwargs)

Outputs a tree of JSON conforming to the speedscope schema documented at

wiki: https://github.com/jlfwong/speedscope/wiki/Importing-from-custom-sources schema: https://www.speedscope.app/file-format-schema.json spec: https://github.com/jlfwong/speedscope/blob/main/src/lib/file-format-spec.ts example: https://github.com/jlfwong/speedscope/blob/main/sample/profiles/speedscope/0.0.1/simple.speedscope.json

  • show_all – Don’t hide library frames - show everything that pyinstrument captures.

  • timeline – Instead of aggregating time, leave the samples in chronological order.

  • processor_options – A dictionary of processor options.


Processors are functions that take a Frame object, and mutate the tree to perform some task.

They can mutate the tree in-place, but also can change the root frame, they should always be called like:

frame = processor(frame, options=...)
pyinstrument.processors.remove_importlib(frame, options)

Removes <frozen importlib._bootstrap frames that clutter the output.

pyinstrument.processors.aggregate_repeated_calls(frame, options)

Converts a timeline into a time-aggregate summary.

Adds together calls along the same call stack, so that repeated calls appear as the same frame. Removes time-linearity - frames are sorted according to total time spent.

Useful for outputs that display a summary of execution (e.g. text and html outputs)

pyinstrument.processors.group_library_frames_processor(frame, options)

Groups frames that should be hidden into FrameGroup objects, according to hide_regex and show_regex in the options dict, as applied to the file path of the source code of the frame. If both match, ‘show’ has precedence. Options:


regular expression, which if matches the file path, hides the frame in a frame group.


regular expression, which if matches the file path, ensures the frame is not hidden

Single frames are not grouped, there must be at least two frames in a group.

pyinstrument.processors.merge_consecutive_self_time(frame, options)

Combines consecutive ‘self time’ frames.

pyinstrument.processors.remove_unnecessary_self_time_nodes(frame, options)

When a frame has only one child, and that is a self-time frame, remove that node and move the time to parent, since it’s unnecessary - it clutters the output and offers no additional information.

pyinstrument.processors.remove_irrelevant_nodes(frame, options, total_time=None)

Remove nodes that represent less than e.g. 1% of the output. Options:


sets the minimum duration of a frame to be included in the output. Default: 0.01.

Internals notes

Frames are recorded by the Profiler in a time-linear fashion. While profiling, the profiler builds a list of frame stacks, with the frames having in format:

function_name <null> filename <null> function_line_number

When profiling is complete, this list is turned into a tree structure of Frame objects. This tree contains all the information as gathered by the profiler, suitable for a flame render.

Frame objects, the call tree, and processors

The frames are assembled to a call tree by the profiler session. The time-linearity is retained at this stage.

Before rendering, the call tree is then fed through a sequence of ‘processors’ to transform the tree for output.

The most interesting is aggregate_repeated_calls, which combines different instances of function calls into the same frame. This is intuitive as a summary of where time was spent during execution.

The rest of the processors focus on removing or hiding irrelevant Frames from the output.

Self time frames vs. frame.self_time

Self time nodes exist to record time spent in a node, but not in its children. But normal frame objects can have self_time too. Why? frame.self_time is used to store the self_time of any nodes that were removed during processing.