# Statement class

(Shortest import: `from brian2.codegen.statements import Statement)`

class brian2.codegen.statements.Statement(var, op, expr, comment, dtype, constant=False, subexpression=False, scalar=False)

  Bases: `object`

  A single line mathematical statement.

  The structure is `var op expr`.

  Parameters:

    var : str

    > The left hand side of the statement, the value being written to.

    op : str

    > The operation, can be any of the standard Python operators (including `+=` etc.) or a special operator `:=` which means you are defining a new symbol (whereas `=` means you are setting the value of an existing symbol).

    expr : str, `Expression`

    > The right hand side of the statement.

    dtype : `dtype`

    > The numpy dtype of the value or array `var`.

    constant : bool, optional

    > Set this flag to `True` if the value will not change (only applies for `op==':='`.

    subexpression : bool, optional

    > Set this flag to `True` if the variable is a subexpression. In some languages (e.g. Python) you can use this to save a memory copy, because you don’t need to do `lhs[:] = rhs` but a redefinition `lhs = rhs`.

    scalar : bool, optional

    > Set this flag to `True` if `var` and `expr` are scalar.

  Notes

  Will compute the following attribute:

  `inplace`

    True or False depending if the operation is in-place or not.

  Boolean simplification notes:

  Will initially set the attribute `used_boolean_variables` to `None`. This is set by `optimise_statements` when it is called on a sequence of statements to the list of boolean variables that are used in this expression. In addition, the attribute `boolean_simplified_expressions` is set to a dictionary with keys consisting of a tuple of pairs `(var, value)` where `var` is the name of the boolean variable (will be in `used_boolean_variables`) and `var` is `True` or `False`. The values of the dictionary are strings representing the simplified version of the expression if each `var=value` substitution is made for that key. The keys will range over all possible values of the set of boolean variables. The complexity of the original statement is set as the attribute `complexity_std`, and the complexity of the simplified versions are in the dictionary `complexities` (with the same keys).

  This information can be used to generate code that replaces a complex expression that varies depending on the value of one or more boolean variables with an `if/then` sequence where each subexpression is simplified. It is optional to use this (e.g. the numpy codegen does not, but the cython one does).