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# -*- coding: utf-8 -*-
This module tries to optimize template trees by:
* eliminating constant nodes
* evaluating filters and macros on constant nodes
* unroll loops on constant values
* replace variables which are already known (because they doesn't
change often and you want to prerender a template) with constants
After the optimation you will get a new, simplier template which can
be saved again for later rendering. But even if you don't want to
prerender a template, this module might speed up your templates a bit
if you are using a lot of constants.
:copyright: Copyright 2008 by Christoph Hack.
:license: GNU GPL.
from copy import deepcopy
from jinja2 import nodes
from jinja2.visitor import NodeVisitor, NodeTransformer
from jinja2.runtime import subscribe
class ContextStack(object):
"""Simple compile time context implementation."""
def __init__(self, initial=None):
self.stack = [{}]
if initial is not None:
self.stack.insert(0, initial)
def push(self):
def pop(self):
def __getitem__(self, key):
for level in reversed(self.stack):
if key in level:
return level[key]
raise KeyError(key)
def __setitem__(self, key, value):
self.stack[-1][key] = value
def blank(self):
"""Return a new context with nothing but the root scope."""
return ContextStack(self.stack[0])
class Optimizer(NodeTransformer):
def __init__(self, environment):
self.environment = environment
def visit_Filter(self, node, context):
"""Try to evaluate filters if possible."""
# XXX: nonconstant arguments? not-called visitors? generic visit!
x = self.visit(node.node, context).as_const()
except nodes.Impossible:
return self.generic_visit(node, context)
for filter in reversed(node.filters):
# XXX: call filters with arguments
x = self.environment.filters[](x)
# XXX: don't optimize context dependent filters
return nodes.Const(x)
def visit_For(self, node, context):
"""Loop unrolling for iterable constant values."""
iterable = iter(self.visit(node.iter, context).as_const())
except (nodes.Impossible, TypeError):
return self.generic_visit(node, context)
result = []
# XXX: tuple unpacking (for key, value in foo)
target =
iterated = False
for item in iterable:
context[target] = item
result.extend(self.visit(n, context) for n in deepcopy(node.body))
iterated = True
if not iterated and node.else_:
result.extend(self.visit(n, context) for n in deepcopy(node.else_))
return result
def visit_If(self, node, context):
val = self.visit(node.test, context).as_const()
except nodes.Impossible:
return self.generic_visit(node, context)
if val:
return node.body
return node.else_
def visit_Name(self, node, context):
if node.ctx == 'load':
return nodes.Const(context[], lineno=node.lineno)
except KeyError:
return node
def visit_Assign(self, node, context):
target = = self.generic_visit(, context)
value = self.generic_visit(node.node, context).as_const()
except nodes.Impossible:
return node
result = []
lineno = node.lineno
def walk(target, value):
if isinstance(target, nodes.Name):
const_value = nodes.Const(value, lineno=lineno)
result.append(nodes.Assign(target, const_value, lineno=lineno))
context[] = value
elif isinstance(target, nodes.Tuple):
value = tuple(value)
except TypeError:
raise nodes.Impossible()
if len(target) != len(value):
raise nodes.Impossible()
for name, val in zip(target, value):
walk(name, val)
raise AssertionError('unexpected assignable node')
walk(target, value)
except nodes.Impossible:
return node
return result
def visit_Subscript(self, node, context):
if node.ctx == 'load':
item = self.visit(node.node, context).as_const()
arg = self.visit(node.arg, context).as_const()
except nodes.Impossible:
return self.generic_visit(node, context)
return nodes.Const(subscribe(item, arg, 'load'))
return self.generic_visit(node, context)
def optimize(node, environment, context_hint=None):
"""The context hint can be used to perform an static optimization
based on the context given."""
optimizer = Optimizer(environment)
return optimizer.visit(node, ContextStack(context_hint))
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