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What is ast.Delete(targets) in Python?

Abdul Monum
Abstract Syntax Tree

ast.Delete(targets) is a class defined in the ast module that expresses the del statement in Python in the form of an Abstract Syntax Treetree representation of source code. When the parse() method of ast is called on a Python source code that contains the del keyword, the ast.Delete class is invoked, which expresses the del statement to a node in an ast tree data structure. The ast.Delete class represents the Delete node type in the ast tree. In the class parameter, targets contains the list of nodes on which the del statement is called. The target node types can be any of the following:

  • Name: a variable in Python.
  • Attribute: an attribute of a Python object such as student.age.
  • Subscript: a subscripted object such as b[1].

Example

import ast
from pprint import pprint

class DeleteVisitor(ast.NodeVisitor):

    def visit_Delete(self, node):
        print('Node type: Delete\nFields:', node._fields)
        ast.NodeVisitor.generic_visit(self, node)


    def visit_Name(self, node):
        print('Node type: Name\nFields:', node._fields)
        ast.NodeVisitor.generic_visit(self, node)


visitor = DeleteVisitor()
tree = ast.parse('del a,b,c')
pprint(ast.dump(tree))
visitor.visit(tree)

Explanation

  • We define a DeleteVisitor class that extends from the parent class ast.NodeVisitor. We override the predefined visit_Delete and visit_Name methods in the parent class, which receive the Delete and Name nodes, respectively. In the method, we print the type and the fields inside the node and call the generic_visit() method, which invokes the propagation of visit on the children nodes of the input node.
  • We initialize a visitor object of the class DeleteVisitor.
  • We write the Python statement del a,b,c and send it to the ast.parse() method, which returns the result of the expression after evaluation, then store it in tree.
  • The ast.dump() method returns a formatted string of the tree structure in tree.
  • The visit method available to the visitor object visits all the nodes in the tree structure.

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