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Toolkit for reading and interacting with ENDF-6 formatted files


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Continuous Integration


Toolkit for reading and interacting with ENDF-6 formatted files. This toolkit provides a full C++ library along with python bindings.

Release and development versions

For the latest version of ENDFtk and an overview of the latest changes, please see the Release Notes or the release page.

The latest release version of ENDFtk can always be found at the head of the main branch of this repository and every release is associated to a release tag. New versions are released on a regular basis (we aim to provide updates at least every three months). The latest development version of ENDFtk containing the latest updates and changes can be found in at the head of the develop branch. This development version should be used with caution.

ENDFtk in python

Installing ENDFtk for python

First of all, a user should clone the ENDFtk repository and build the python bindings:

git clone
cd ENDFtk
mkdir build
cd build
cmake -DCMAKE_BUILD_TYPE=Release ../
make -j8

The compilation will produce a number of dynamic libraries linked to the python libraries on the user's computer (these will be named something like < component > with < component > the name of the component). The names of these dynamic libraries will also indicate which version of the python libraries they are linked against. This is important since you will need to use the associated python version along with them.

ENDFtk in python requires python 3.x so you will need to have at least one python 3.x installed. When multiple python versions are installed, it may be beneficial to include -DPYTHON_EXECUTABLE=$(which python3) in the cmake configuration step so that the default python3 version will be picked.

In order to use the ENDFtk python package, the user should make sure that the library is within the python path. This can be done in multiple ways. You can set that up by adding the ENDFtk build path to the python path $PYTHONPATH environmental variable on your machine, or by using the following in your python code:

import sys
sys.path.append( < ENDFtk-build-path > )

where < ENDFtk-build-path > is the path to the ENDFtk python dynamic library.

When running python in the build directory directly, none of these steps are required.


c++: Permission denied

On MacOS, an error may occur when using make -j8 telling the user that there is no permission to execute the compiler (the error message will contain the full path to the compiler executable). This error is related to an issue with the MacOS system default make installation not allowing parallel compilation (the -j8 part of the make command). Executing make without a parallel option will function, but the user should consider installing a different version of make (e.g. using homebrew) to get around this.

CMake doesn’t detect the right Python version

Taken from the pybind11 FAQ.

The CMake-based build system will try to automatically detect the installed version of Python and link against that. When this fails, or when there are multiple versions of Python and it finds the wrong one, delete CMakeCache.txt and then add -DPYTHON_EXECUTABLE=$(which python) to your CMake configure line. (Replace $(which python) with a path to python if your prefer.)

A version of python 3.x is preferred.

ImportError cannot import name

This error sometimes comes up when running the cmake command. This appears to be related to an incomplete/corrupted python installation. It can be rectified by installing the distutils package for the python version that is being used. On a linux system, the following command should install the distutils package:

sudo apt install python3-distutils
ImportError `GLIBCXX_3.4.30' not found

A problem may occur if a user's installed python environment is through conda. The user will be able to build properly but all of the unit tests for python may fail due to GLIBCXX_3.4.30 being missing. This seems to be an a problem with conda not having GLIBCXX_3.4.30 in the path. If the user is able to compile ENDFtk, they have GLIBCXX_3.4.30. At which point, a symlink will need to be created to point the conda enviroment to where GLIBCXX_3.4.30 is installed.

cannot find python.h

When compiling the python bindings, this error indicates that the python header files and static library we need to link to are not installed on your system. This appears to be related to an incomplete python installation. It can be rectified by installing the python3-dev package (when using python 3). On a linux system, the following command should install the header files:

sudo apt install python3-dev

A minimal user guide:

Opening up a tape:

import ENDFtk
tape = ENDFtk.tree.Tape.from_file( 'n-001_H_001.endf' )

An ENDFtk.tree.Tape effectively indexes the file into available materials, files and sections, which can be parsed at will by the user. The ENDFtk.tree submodule also provides an ENDFtk.tree.Material, ENDFtk.tree.File and ENDFtk.tree.Section that the user can look through before parsing the data that is contained in any of these. Parsing the data requires strict adherence to the ENDF6 format but loading the data into an ENDFtk.tree.Tape does not. As a result, the ENDFtk.tree.Tape is also capable of indexing older ENDF files that do not conform with the ENDF6 standard (tests have shown that we can index files as old as ENDF/B-II).

Once the data is indexed, a user can retrieve an/or parse components (entire materials, files or sections) as follows:

mat = tape.material(125).parse()
file = tape.material(125).file(6).parse()
section = tape.material(125).file(6).section(102).parse()

Accessing the underlying files and sections from parsed materials and sections uses the same function names:

mat = tape.material(125).parse()
file = mat.file(6)
section = file.section(102)

but since they are already parsed, no need to use the .parse() at the end. There are also ENDF-speak equivalents to this for both the ENDFtk.tree components as well as the parsed components:

mat = tape.MAT(125).parse()
file = mat.MF(6)
section = file.MT(102)

Every component in ENDFtk has python documentation associated to it that can be viewed using the help(...) function in python:

mat = tape.material(125).parse()
file = tape.material(125).file(6).parse()
section = tape.material(125).file(6).section(102).parse()
help( section ) # this will display the help for an ENDF MF6 section

A simple example for looking at the different secondary particles and the distribution types used for them:

pu = tape.material(9437).parse()
for product in pu.file(6).section(102).reaction_products :

    print( product.ZAP, product.LAW )

ENDFtk uses a concept called ranges (aka sequences) so as a result, anything coming out as a range will be a custom type. These custom range types allow subscripting and iteration like any other sequence or list. To convert such a range into a proper list, you can use the to_list() method or slicing. This will do a deep copy of primitive types (int, doubles, etc.). It will not do a deep copy for custom types like sections or underlying components. To deep copy a range of custom types, a user can use the copy() method on the range.

For example:

file = tape.material(125).file(6).parse()
sections = file.sections           # this is the custom range type for MF6 sections
sections = file.sections.to_list() # this is a list of MF6 sections, with the same memory address as those contained in the file object

sections = file.sections[:]        # this is also a list of MF6 sections, with the same memory address as those contained in the file object
sections = file.sections.copy()    # this is a list of MF6 sections that have been copied, with a different memory address as those contained in the file object


This software is copyrighted by Los Alamos National Laboratory and distributed according to the conditions in the accompanying LICENSE file.