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Bindings to Ipopt C++ library.

Project description

Pypopt: Ipopt for Python

Pypopt is an Ipopt wrapper for Python. The aim is to expose the same API as Ipopt C++ interface.


You can find examples in the examples/ folder.


In Pypopt you can use Python objects as targets for Ipopt journaling. The Python objects needs to implement two methods:

  • write(str): called to write str to the stream object

  • flush(): called to flush the stream

This means we can use Python3 io.StringIO to capture Ipopt output to string:

app = IpoptApplication()
f = io.StringIO()
j = PythonJournal(EJournalLevel.J_NONE, f)
jnlst = app.journalist()


  • A working C++ compiler

  • Cython

  • Ipopt

  • Pytest + pytest-runner + pytest-cov for testing

Ipopt Installation

We recommend installing Ipopt from source.

If you have Ipopt installed in a different location than /usr set the following environment variables before proceeding to the next section:



Pypopt is available on Pypi:

pip install pypopt

Installation from Source

To install pypopt simply run:

python install


Pypopt is a Cython extension, this makes it sometimes tricky to install correctly.

Different toolchain for Ipopt and Pypopt

Ipopt and Pypopt need to be compiled with the same C++ toolchain. If that’s not the case, you will see an error like the following when loading Pypopt:

Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/lib/python3.6/site-packages/pypopt/", line 24, in <module>
  from pypopt._cython import (
ImportError: /lib/python3.6/site-packages/pypopt/ undefined symbol: _ZN5Ipopt7Journal4NameB5cxx11Ev

This means Ipopt and Pypopt were compiled with different compilers/flags. To fix this issue install Ipopt from source and set the IPOPT_INCLUDE_DIR and IPOPT_LIBRARY_DIR environment variables to your Ipopt installation.


Copyright 2018 Francesco Ceccon

Licensed under the Apache License, Version 2.0 (the “License”); you may not use this file except in compliance with the License. You may obtain a copy of the License at

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an “AS IS” BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.


0.5.0 (2020-04-28)

  • Improve TNLP interface for optimal performance

  • Implement Pyomo direct solver interface

0.4.2 (2018-07-05)

  • Documentation update

0.4.1 (2018-07-05)

  • Fix

0.4.0 (2018-07-05)

  • Changes to TNLP interface

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