core.rst

Marvin internals (marvin.core)

This section describes how Marvin works internally. Most users do not need to understand all of these details. However, they are important if you plan to write contributed code or if you are forking Marvin.

Regardless of how you use Marvin, it is always a good idea to have a general understanding of the configuration <marvin-config-info> system and the data access modes <marvin-dam>.

MarvinToolsClass

.MarvinToolsClass is the main class from which most Marvin tool classes subclass (e.g., ~marvin.tools.cube.Cube or ~marvin.tools.maps.Maps). It encapsulates the data access decision tree <mode-decision-tree> and implements high level methods such as .MarvinToolsClass.download and .MarvinToolsClass._getFullPath for using the tree <https://github.com/sdss/tree> product to determine paths and download <marvin-download-objects> files. In general, any class that represents a file should subclass from .MarvinToolsClass.

.MarvinToolsClass uses abc.ABCMeta as a metaclass to mark abstractmethods <abc.abstractmethod>. Any subclass must override and define .MarvinToolsClass._getFullPath and .MarvinToolsClass._set_datamodel.

Generic methods for pickling <pickle> and unpickling the subclassed objects are implemented in .MarvinToolsClass.save and .MarvinToolsClass.restore. While these work in most cases, depending on the specifics of the subclass some additional handling may be necessary.

marvin.tools.core.MarvinToolsClass

Mixins

Some features are implemented in the form of mixins: parent classes that provide modular functionality. In particular, mixins are provided for accessing the NSA parameters for an object, and the DAPall information.

.NSAMixIn must be called with when initialising the child class, and passed the source of the NSA data. .DAPallMixIn does not need to be instantiated, and uses ~.MarvinToolsClass.release to determine the location of the DAPall file.

An example of a class that uses both .NSAMixIn and .DAPallMixIn would be

class MyClass(MarvinToolsClass, NSAMixIn, DAPallMixIn):

    def __init__(self, **kwargs):

        MarvinToolsClass.__init__(self, **kwargs)
        NSAMixIn.__init__(self, **kwargs)

    # Overrides abstractmethods
    def _getFullPath(self):
       pass

    def _set_datamodel(self):
       pass

note that we use a direct call to __init__ instead of super to make sure that both parent classes are initialised.

marvin.tools.core

Further reading

• The configuration class (marvin.config <marvin-config-info>)
• marvin-dam
• marvin-download-objects