# Equations and namespaces

## Equation parsing

Parsing is done via pyparsing, for now find the grammar at the top of the `brian2.equations.equations` file.

## Variables

Each Brian object that saves state variables (e.g. `NeuronGroup`, `Synapses`, `StateMonitor`) has a `variables` attribute, a dictionary mapping variable names to `Variable` objects (in fact a `Variables` object, not a simple dictionary). `Variable` objects contain information about the variable (name, dtype, units) as well as access to the variable’s value via a `get_value` method. Some will also allow setting the values via a corresponding `set_value` method. These objects can therefore act as proxies to the variables’ “contents”.

`Variable` objects provide the “abstract namespace” corresponding to a chunk of “abstract code”, they are all that is needed to check for syntactic correctness, unit consistency, etc.

## Namespaces

The `namespace` attribute of a group can contain information about the external (variable or function) names used in the equations. It specifies a group-specific namespace used for resolving names in that group. At run time, this namespace is combined with a “run namespace”. This namespace is either explicitly provided to the `Network.run` method, or the implicit namespace consisting of the locals and globals around the point where the run function is called is used. This namespace is then passed down to all the objects via `Network.before_fun` which calls all the individual `BrianObject.before_run` methods with this namespace.