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88 lines
3.2 KiB
Python
88 lines
3.2 KiB
Python
8 years ago
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# -*- coding: utf-8 -*-
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"""
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jinja2.visitor
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~~~~~~~~~~~~~~
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This module implements a visitor for the nodes.
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:copyright: (c) 2017 by the Jinja Team.
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:license: BSD.
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"""
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from jinja2.nodes import Node
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class NodeVisitor(object):
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"""Walks the abstract syntax tree and call visitor functions for every
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node found. The visitor functions may return values which will be
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forwarded by the `visit` method.
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Per default the visitor functions for the nodes are ``'visit_'`` +
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class name of the node. So a `TryFinally` node visit function would
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be `visit_TryFinally`. This behavior can be changed by overriding
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the `get_visitor` function. If no visitor function exists for a node
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(return value `None`) the `generic_visit` visitor is used instead.
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"""
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def get_visitor(self, node):
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"""Return the visitor function for this node or `None` if no visitor
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exists for this node. In that case the generic visit function is
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used instead.
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"""
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method = 'visit_' + node.__class__.__name__
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return getattr(self, method, None)
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def visit(self, node, *args, **kwargs):
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"""Visit a node."""
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f = self.get_visitor(node)
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if f is not None:
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return f(node, *args, **kwargs)
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return self.generic_visit(node, *args, **kwargs)
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def generic_visit(self, node, *args, **kwargs):
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"""Called if no explicit visitor function exists for a node."""
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for node in node.iter_child_nodes():
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self.visit(node, *args, **kwargs)
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class NodeTransformer(NodeVisitor):
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"""Walks the abstract syntax tree and allows modifications of nodes.
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The `NodeTransformer` will walk the AST and use the return value of the
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visitor functions to replace or remove the old node. If the return
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value of the visitor function is `None` the node will be removed
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from the previous location otherwise it's replaced with the return
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value. The return value may be the original node in which case no
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replacement takes place.
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"""
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def generic_visit(self, node, *args, **kwargs):
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for field, old_value in node.iter_fields():
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if isinstance(old_value, list):
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new_values = []
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for value in old_value:
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if isinstance(value, Node):
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value = self.visit(value, *args, **kwargs)
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if value is None:
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continue
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elif not isinstance(value, Node):
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new_values.extend(value)
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continue
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new_values.append(value)
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old_value[:] = new_values
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elif isinstance(old_value, Node):
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new_node = self.visit(old_value, *args, **kwargs)
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if new_node is None:
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delattr(node, field)
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else:
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setattr(node, field, new_node)
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return node
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def visit_list(self, node, *args, **kwargs):
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"""As transformers may return lists in some places this method
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can be used to enforce a list as return value.
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"""
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rv = self.visit(node, *args, **kwargs)
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if not isinstance(rv, list):
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rv = [rv]
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return rv
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