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How to Contribute


Send your PR! Thanks!

Slightly more Details

You want to contribute? That's very generous of you and we are truly grateful! Small changes, like fixing typos in documentation are completely fine and also most welcome. For bigger changes, we suggest that you open an issue before you start coding, so that we can maximize the probability that we can successfully merge in your code.

R, C or Python

Fork the appropriate igraph repository at github: The igraph C library is in, the Python interface is in The R interface is in

An enhancement that is specific to R or Python or C (or a subset) is prefectly fine. You are not obliged to write wrappers in both R or Python. E.g. updating plotting code in R or Python is also fine.

This document is concerned with the igraph C library.

Making Trivial Changes

  • Please always use the master branch. Choose this branch in your fork.
  • Then look for the file you want to modify.
  • Clique on the edit symbol (pen) on the upper right corner of the file view.
  • Make your edits.
  • Write a short commit message, less than 65 characters. E.g. "Fix C docs typo" or "Fix degree bug for loops". If needed, elaborate your changes below in the "extended description" field.
  • Commit your changes.
  • Go back to the start page of your forked repository. It is at<username>/igraph.
  • Click on the green button before the branch name to create a pull request.
  • Click on "Create pull request".
  • Provide a more detailed description if you like. Please also indicate that you are fine with licensing your contribution under igraph's license (see Legal Stuff below).
  • Click on "Create pull request".
  • That's it! It is probably a good idea to keep your forked repository until the change is accepted into igraph, in case you need to modify it.
  • Now you need to wait for us, unfortunately. Please ping us, if it takes long to respond. E.g. a week is considered to be long.
  • Once your pull request is accepted, you can delete your forked repository.

Making More Involved Changes

This is mostly the same as for trivial changes, but you probably want to edit the sources on your computer, instead of online on Github.

  • Open an issue in the issue tracker about the proposed changes. This is not required for smaller things, but I suggest you do it for others. Just in case somebody is already working on the same thing, or it is something we don't want in igraph.

  • Fork the repository, and clone it to the machine you'll work on.

  • We usually build igraph on OSX, so the master branch is usally fine on that platform. It might have problems on other systems. If this happens, please open an issue and tell us.

  • Make sure you work on the master branch.

  • Once ready with your changes, build igraph, and run the tests. library this means

    make check
  • Submit your pull request.

  • Now you need to wait for us, unfortunately. Please ping us, if it takes long to respond. E.g. a week is considered to be long.

Writing igraph Code

Some tips on writing igraph code. In general, look at how things are done, and try to do them similarly. (Unless you think they are not done well, in which case please tell us.)

Code Formatting

Look at the style (indentation, braces, etc.) of some recently committed bigger change, and try to mimic that. The code style within igraph is not stricly the same, but we want to keep it reasonably similar.

C vs. C++

Try to use C, unless you are updating already existing C++ code, or you have other good reason for C++ (but then maybe ask us first).

Data types

Please try to use igraph's data types for vectors, matrices, stacks, etc. If they lack some functionality you need, please tell us.

Memory Allocation, Error Handling

Please use igraph's memory allocation functions. Please also use the FINALLY stack: IGRAPH_FINALLY, IGRAPH_FINALLY_CLEAN, etc. See examples in the C code.

Random Numbers

Please look at how random numbers are generated in any function in src/games.c. Do the same. I.e. use RNG_BEGIN, RNG_END, and igraph's RNG calls. Do not use the libc RNGs or other RNGs.


Please document your new functions. The C documentation is included in the C source code.

Test Cases

Unless you change something trivial, please consider adding test cases. This is important! See the tests and the examples/simple directories for existing tests that you can use as examples.

Ask Us!

In general, if you are not sure about something, please ask! You can open an issue on Github, write to the igraph-help mailing list (see the homepage at, or write to Tamás and Gábor. We preper the public forums, though, because then others can learn from it, too.

Legal Stuff

This is a pain to deal with, but we can't avoid it, unfortunately. So, igraph is licensed under the "General Public License (GPL) version 2, or later". The igraph manual is licensed under the "GNU Free Documentation License". If your contribution is bigger than a typo fix, then please indicate that you are fine with releasing your code/text under these licenses. E.g. adding a sentence that reads as "I'm fine with GPL 2 or later and FDL." is perfectly enough.