pglast.visitors — Other ways to inspect and manipulate the AST

class pglast.visitors.Action

Abstract action singleton.

class pglast.visitors.ActionMeta

Metaclass used to implement action singleton.

class pglast.visitors.Add

Marker used to tell the iterator to insert nodes in the current sequence.

class pglast.visitors.Ancestor(parent=None, node=None, member=None)

Simple object to keep track of the node’s ancestors while it’s being visited.

An instance of this class represent a particular ancestor in the hierarchy chain: it carries a reference that points to the higher item in the chain, the associated ast.Node instance and a member, either the attribute name or sequential index in the parent node.

Iteration yields the sequence of involved members, that is the path starting from the root of the AST tree that leads to leaf node.

Accessing an instance with a positive index returns the nth node up in the hierarchy.

When applied (using the @ operator) to an ast.Node instance will traverse that node returning the leaf one corresponding to the whole chain.

Example:

>>> tree = parse_sql('select 1')
>>> root = Ancestor()
>>> root
ROOT
>>> root@tree is tree
True
>>> root[0] is None
True
>>> select_stmt_path = root / (root, 0) / (tree[0], 'stmt')
>>> select_stmt_path
ROOT → 0 → stmt
>>> select_stmt_path@tree is tree[0].stmt
True
>>> select_stmt_path[0] is tree[0]
True
>>> columns_path = select_stmt_path / (tree[0].stmt, 'targetList')
>>> first_col_path = columns_path / (tree[0].stmt.targetList[0], 0)
>>> first_col_path
ROOT → 0 → stmt → targetList → 0
>>> first_col_path[0]
<ResTarget val=<A_Const val=<Integer val=1>>>
>>> first_col_path[1] is columns_path[0]
True

class pglast.visitors.Continue

Marker used to tell the iterator to keep going.

class pglast.visitors.Delete

Marker used to tell the iterator to delete current node.

class pglast.visitors.RelationNames

Concrete implementation of the referenced_relations() function.

Calling an instance of this class will return a set of the names of the relations referenced by the given node.

visit_CommonTableExpr(ancestors, node)

Collect CTE names.

visit_RangeVar(ancestors, node)

Collect relation names.

class pglast.visitors.Skip

Marker used to tell the iterator to not descend into the current node.

class pglast.visitors.Visitor

Base class implementing the visitor pattern.

To use it, you shall write a subclass that implements a set of particular named methods, specifically visit_XYZ where XYZ is the name of a class name defined in the pglast.ast module.

Instances of this class are callables and accept either a pglast.ast.Node instance or a sequence of instances, typically the result of parse_sql. The argument will be traversed in a breadth first order and each Node instance will be passed to the corresponding visit_XYZ method if it is implemented, falling back to the default visit method. If none of them are defined, the node will be ignored.

The visit_XYZ methods receive two arguments: the ancestry chain of the node, an instance of Ancestor and the Node instance itself. The methods may return either None, an action or a new node that will replace the original one.

iterate(node)

Iterate thru node’s AST using a breadth-first traversing.

Parameters

node – either a Node instance or a tuple of those

This is a generator, that yields Node instances together with their ancestors chain as it finds them while traversing the tree.

visit = None

The default visit method for any node without a specific one. When None, nothing happens.

pglast.visitors.referenced_relations(stmt)

Return the set of relation names referenced in the given stmt.

Parameters

stmt – either a string containing the SQL statement or a ast.Node instance

Returns

a set of strings, the names of the relations

Example:

assert referenced_relations('WITH q1(x,y) AS (SELECT 1,2)'
                            ' SELECT * FROM q1, q2') == {'q2'}

pglast.visitors.visitable(node)

Determine whether the given node is visitable or not.