In this section we explain a little bit about namespaces. Namespaces are used frequently in validphys runcards because these runcards are based on reportengine, for which namespaces are a central concept.

A namespace is a stack of python dictionaries which are indexed by a tuple called the namespace specification (nsspec). A user gives some inputs in terms of fuzzyspecs and these are translated into nnspecs. This is mostly an advanced internal implementation detail, but it is important in order to understand how several features work. Also, the abstraction leaks into user-facing features such as the collect function.

Namespace specifications

An nsspec is a tuple of an arbitrary number of elements. Each element in the tuple corresponds to one extra stack layer in depth (“stack frame”). The elements of the tuple can be either:

  • Names of mappings.

  • Names of objects that have an as_namespace method

  • Tuples of the form (name of list of mappings, index).

The scope rules are similar to those of C: the lookup of a value is done first looking at the inner frame and then at the outer ones, until a match is found.

Consider the following example:

   pdf: NNPDF40_nlo_as_01180
   normalize_to: None
   use_cuts: "nocuts"

   pdf: NNPDF40_nnlo_as_01180
   normalize_to: NNPDF40_nnlo_as_01180

 - {use_cuts: "nocuts"}
 - {use_cuts: "fromfit"}

Given the input above, we could form the following nsspec:

('Second', ('cutspecs', 0))

This would correspond to a namespace where we have the following symbols available:

  • use_cuts (set to “nocuts”) from cutspecs.

  • pdf and normalize_to (set to NNLO) from second.

  • First, Second and cutspecs from the root namespace.

We could also form the specification:

(('cutspecs', 1), 'First')

Because the innermost specification is last, the value of use_cuts is “nocuts”.

The function reportengine.namespaces.resolve(ns, nsspec) returns a mapping (in particular it is a modified version of collections.ChainMap) that implements exactly this behaviour. It is used extensively thorough reportengine.


The namespace specifications as described above is not what the user typically enters. Instead, the typical user input is what in the code is labelled fuzzyspec. A fuzzyspec is like an nsspec except that the lists of mappings are entered by name and not by a tuple (name, index). A fuzzyspec resolves to one or more nsspecs. For example, given the fuzzyspec:

('Second', 'cutspecs')

and the input above, it gets expanded into two nsspecs:

('Second', ('cutspecs', 0))
('Second', ('cutspecs', 1))

corresponding to each of the two mappings in cutspecs.

The as_namespace method

An object can customize how it is viewed as a reportengine namespace. This is done by defining a method called as_namespace, which takes no arguments and should return either a mapping or a list of mappings. This is used to implement parsing lists automatically.