# Source code for brian2.codegen.statements

```
"""
Module providing the `Statement` class.
"""
[docs]class Statement:
"""
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 `~brian2.codegen.optimisation.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).
"""
def __init__(
self,
var,
op,
expr,
comment,
dtype,
constant=False,
subexpression=False,
scalar=False,
):
self.var = var.strip()
self.op = op.strip()
self.expr = expr
self.comment = comment
self.dtype = dtype
self.constant = constant
self.subexpression = subexpression
self.scalar = scalar
if constant and self.op != ":=":
raise ValueError(f"Should not set constant flag for operation {self.op}")
if op.endswith("=") and op != "=" and op != ":=":
self.inplace = True
else:
self.inplace = False
self.used_boolean_variables = None
self.boolean_simplified_expressions = None
def __str__(self):
s = f"{self.var} {self.op} {str(self.expr)}"
if self.constant:
s += " (constant)"
if self.subexpression:
s += " (subexpression)"
if self.inplace:
s += " (in-place)"
if len(self.comment):
s += f" # {self.comment}"
return s
__repr__ = __str__
```