Guppy 3

A Python Programming Environment & Heap analysis toolset

Guppy A fish swimming in Python
Heapy Heap Analysis Toolset
GSL Guppy Specification Language

This is the home page for Guppy 3 , a programming environment providing object and heap memory sizing, profiling and analysis. It includes a prototypical specification language that can be used to formally specify aspects of Python programs and generate tests and documentation from a common source.

Guppy 3 is a fork of Guppy-PE , created by Sverker Nilsson for Python 2.


Guppy is an umbrella package combining Heapy and GSL with support utilities such as the Glue module that keeps things together.

The name guppy was chosen because Nilsson found it in a backward-dictionary as a word ending with py and he thought it was cute enough and that it would not so likely conflict with some other package name. It was to be a general name since all kinds of packages should fit under this top level name.


The aim of Heapy is to support debugging and optimization regarding memory related issues in Python programs.

Such issues can make a program use too much memory, making it slow by itself as well as slowing down an entire server, or it may fail to run at all in a limited memory device such as a mobile phone.

The primary motivation for Heapy is that there has been a lack of support for the programmer to get information about the memory usage in Python programs. Heapy is an attempt to improve this situation. A project with a similar intent is PySizer.

The problem situation has a number of aspects, which Nilsson think can be characterised, for example, as follows.

As Heapy has evolved, with considerations like this in mind, it currently provides the following features.

Data gathering

  • Finds reachable and/or unreachable objects in the object heap, and collects them into special C-implemented 'nodesets'. Can get data about the objects such as their sizes and how they refer to each other.
  • Uses a C library that can get data about non-standard types from extension modules, given a function table.
  • Optionally uses multiple Python interpreters in the same process, so one can monitor the other transparently.

Data processing

  • Algebraic set operations, for example the set difference can be used to extract the objects allocated after a reference point in time.
  • Various classifications of object sets, and different classifiers can be combined.
  • Shortest paths to a set of objects from other objects, which can be used to find out why the objects are retained in memory.
  • Calculation of the 'dominated' set from a set of root objects which yields the set of objects that would be deallocated if the root objects were deallocated.


  • Tables where each row represents a classification of data.
  • Lists of shortest paths where the edges show the relationships found between the underlying C objects.
  • Reference pattern, presenting a spanning tree of the graph with sets of objects treated as a unit.
  • Limits the number of rows when presentation objects are shown, without depending on an external pager.
  • An interactive graphical browser program can show a time sequence of classified heap data sets as a graph together with a table detailing the data at a specific time or the difference between two points in time.

Portability aspects

  • Can be used with an unmodified C Python, back to version 3.5 AFAIK. Does not depend on any external unix-specific or other utilities.
  • Requires Tk if the graphical browser is to be used.
  • Can not be used with Jython or other non-C Python versions.

System aspects

  • A general 'glue' model provides a session context that imports modules and creates objects automatically when accessed. The glue model is not Heapy specific but is used throughout Guppy and could be used by other packages as well.
  • The glue model makes it practical to have everything in Guppy being dynamically allocated in a session context, so there is no need for any global module-level variables. The modules themself are stored as usual in sys.modules but they are not modified.
  • To be true there is one exception Nilsson come to think of but it is really exceptional.

Heapy has been used during development of itself and of the other parts of Guppy. It has been used to tell how much memory the parts of compound objects use, to see what could be worthwhile to optimize. It was used to find a memory leak in the Heapy profile browser, and to find out the cause, which as far as Nilsson can tell was due to a bug in a library routine which he have reported.


The Guppy Specification Language is an evolving specification language. Nilsson started experimenting with this language because he felt the need to have a way to specify documentation and tests from the same source. GSL can describe aspects of a system, especially its API, in a way that can be automatically converted to tests as well as to documents. The documents generated have a formal structure for describing the formal aspects of the specification, complemented with descriptive text from the same source documents. A language that is similar in intent is the Assertion Definition Language .

Specifications written in GSL can be used for:

GSL has been used to generate the documentation for this Guppy distribution. Some part of the specification has been checked against the implementation using the generated tests, which did reveal some discrepancies that were subsequently corrected.

The documents generated by GSL use a formal syntax to describe parameter modes. This document contains examples of such parameter descriptions and explains what they mean.


Some documentation is included with the source code distribution and can also be browsed here via the following links.

Getting started with Heapy An example of how to get started with Heapy
Document example Explains the meaning of some aspects of the documents.
Guppy Specification of guppy , the top level module.
Profile Browser How to use the graphical heap profile browser.
Screenshot Example showing the graphical heap profile browser in action.
GSL The Guppy Specification Language.
heapyc Specification of the heapyc extension module. Note that this is an internal interface and may be subject to change.
sets Specification of the interface to the setsc extension module which contains bitsets and nodesets.

The following documentation is not included with the source code.

heapy-thesis.pdf The master's thesis, "Heapy: A Memory Profiler and Debugger for Python", which presents background, design, implementation, rationale and some use cases for Heapy (version 0.1).
Metadata and Abstract Published at Linköping University Electronic Press.
heapy-presentation.pdf Slides from the presentation.

External resources

Thanks to all that have written about Heapy on various blogs. Nilsson and I think the following links may be especially useful to get started. More tips are very welcome!


The latest version is in the git repository.

To check out the latest revision, you can do:

git clone guppy



The author, YiFei Zhu, may be contacted at:
Please report bugs preferably via the GitHub issue tracker
The GitHub project page is:

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