ytree is developed using the same conventions as yt. The yt Developer Guide is a good reference for code style, communication with other developers, working with git, and issuing pull requests. Below is a brief guide of aspects that are specific to ytree.
Contributing in a Nutshell¶
Step zero, get out of that nutshell!
After that, the process for making contributions to ytree is roughly as follows:
- Fork the main ytree repository.
- Create a new branch.
- Make changes.
- Run tests. Return to step 3, if needed.
- Issue pull request.
The yt Developer Guide and github documentation will help with the mechanics of git and pull requests.
The ytree source comes with a series of tests that can be run to ensure nothing unexpected happens after changes have been made. These tests will automatically run when a pull request is issued or updated, but they can also be run locally very easily. At present, the suite of tests for ytree takes about three minutes to run.
The first order of business is to obtain the sample datasets. See
Sample Data for how to do so. Next, ytree must be configure to
know the location of this data. This is done by creating a configuration
file in your home directory at the location
$ mkdir -p ~/.config/ytree $ echo [ytree] > ~/.config/ytree/ytreerc $ echo test_data_dir = /Users/britton/ytree_data >> ~/.config/ytree/ytreerc $ cat ~/.config/ytree/ytreerc [ytree] test_data_dir = /Users/britton/ytree_data
This path should point to the outer directory containing all the sample datasets.
Run the Tests¶
Before running the tests, you will the
These can be installed with pip.
$ pip install pytest flake8
Once installed, the tests are run from the top level of the ytree source.
$ pytest tests ============================= test session starts ============================== platform darwin -- Python 3.6.0, pytest-3.0.7, py-1.4.32, pluggy-0.4.0 rootdir: /Users/britton/Documents/work/yt/extensions/ytree/ytree, inifile: collected 16 items tests/test_arbors.py ........ tests/test_flake8.py . tests/test_saving.py ... tests/test_treefarm.py .. tests/test_ytree_1x.py .. ========================= 16 passed in 185.03 seconds ==========================
Adding Support for a New Format¶
Arbor class is reasonably
generalized such that adding support for a new file format
should be relatively straightforward. The existing frontends
also provide guidance for what must be done. Below is a brief
guide for how to proceed. If you are interested in doing this,
we will be more than happy to help!
Where do the files go?¶
As in yt, the code specific to one file format is referred to as a
“frontend”. Within the ytree source, each frontend is located in
its own directory within
ytree/arbor/frontends. Name your
directory using lowercase and underscores and put it in there.
To allow your frontend to be directly importable at run-time, add
the name to the
_frontends list in
Building Your Frontend¶
To build a new frontend, you will need to make frontend-specific
subclasses for a few components. The easiest way to do this is
to start with a blank
Arbor subclass first. Create a sample
script that loads your data with
the number of trees, and queries some fields. Within the base classes,
the necessary functions will raise a
NotImplementedError if you
have not added them yet. Keep running your script and implementing
the function raising this error and before you know it, you’ll be
The components and the files in which they belong are:
- The file i/o (
- Recognizing frontend-specific fields (
In addition to this, you will need to add a file called
which will allow your code to be imported. This file should minimally
import the frontend-specific
Arbor class. For example, the
__init__.py looks like this:
from ytree.arbor.frontends.consistent_trees.arbor import \ ConsistentTreesArbor
Two Types of Arbors¶
There are generally two types of merger-tree data that ytree ingests:
1. all merger-tree data (full trees, halos, etc.) contained within a single file. An example of this is the consistent-trees frontend.
2. halos in files grouped by redshift (halo catalogs) that contain the halo id for the descendent halo which lives in the next catalog. An example of this is the rockstar frontend.
Depending on your case, different base classes should be subclassed. This is discussed below.
Arbor subclass should appear a function called
_is_valid. This function is used by
to determine if the provide file is the correct type. This function
can examine the file’s naming convention and/or open it and inspect
its contents, whatever is required to uniquely identify your frontend.
Have a look at the various examples.
Merger-Tree Data in One File (or a few)¶
If this is your case, then the consistent-trees and “ytree” frontends are the best examples to follow.
arbor.py, your subclass of
Arbor should implement two
_parse_parameter_file: This is the first thing called when your
dataset is loaded. It is responsible for determining things like
box size, cosmological parameters, and the list of fields.
_plant_trees: This function is responsible for constructing the
array containing the roots of all trees in the
should not fully build the trees, but just create
TreeNode instances for each root
and put them in the array.
io.py, you will implement the machinery responsible for
reading field data from disk. You must create a subclass of
TreeFieldIO class and implement
_read_fields function. This function accepts a single
root node (a
TreeNode that is the root of a tree) and a list
of fields and should return a dictionary with NumPy arrays for
Halo Catalog-style Data¶
If this is your case, then the rockstar and tree_farm frontends are the best examples to follow.
arbor.py, your subclass should implement two functions,
_get_data_files. The purpose of
_parse_parameter_file is described above.
_get_data_files: This type of data is usually loaded by
providing one of the set of files. This function needs to figure
out how many other files there are and their names and construct a
list to be saved.
io.py, you will create a subclass of
CatalogDataFile and implement two functions:
_parse_header: This function reads any metadata specific to this
halo catalog. For exmaple, you might get the current redshift here.
_read_fields: This function is responsible for reading field
data from disk. This should minimally take a list of fields and
return a dictionary with NumPy arrays for each field for all halos
contained in the file. It should also, optionally, take a list of
TreeNode instances and return fields
only for them.
Field Units and Aliases (
FieldInfoContainer class holds
information about field names and units. Your subclass can define
known_fields tuple is used to set units for fields on disk.
This is useful especially if there is no way to get this information
from the file. The convention for each entry is (name on disk, units).
By creating aliases to standardized names, scripts can be run on
multiple types of data with little or no alteration for
frontend-specific field names. This is done with the
tuple. The convention for each entry is (alias name, name on disk,
from ytree.arbor.fields import \ FieldInfoContainer class NewCodeFieldInfo(FieldInfoContainer): known_fields = ( # name on disk, units ("Mass", "Msun/h"), ("PX", "kpc/h"), ) alias_fields = ( # alias name, name on disk, units for alias ("mass", "Mass", "Msun"), ("position_x", "PX", "Mpc/h"), ... )
You made it!¶
That’s all there is to it! Now you too can do whatever it is people do with merger-trees. There are probably important things that were left out of this document. If you find any, please consider making an addition or opening an issue. If you’re stuck anywhere, don’t hesitate to ask for help. If you’ve gotten this far, we really want to see you make it to the finish!
Everyone Loves Samples¶
It would be especially great if you could provide a small sample dataset
with your new frontend, something less than a few hundred MB if possible.
This will ensure that your new frontend never gets broken and
will also help new users get started. Once you have some data, make an
addition to the arbor tests by following the example in
tests/test_arbors.py. Then, contact Britton Smith to arrange for
your sample data to be added to the ytree data
collection on the yt Hub.
Ok, now you’re totally done. Take the rest of the afternoon off.