What is ast.BoolOp(op, values) in Python?

Abstract Syntax tree

ast.BoolOp(op, values) is a class defined in the ast module that is used to illustrate boolean expressions 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 boolean operators and or or, the ast.BoolOp(op, values) class is invoked to convert the boolean expression to an ast tree data structure.

The op parameter in the class definition refers to the boolean operators and or or in the expression, and values refers to the values involved in the expression.

Note: Consecutive boolean operations with the same operator, e.g., x and y and z, are collapsed in a single node with all values x,y,z.

Example

import ast
from pprint import pprint
class BoolOpVisitor(ast.NodeVisitor):
    def visit_BoolOp(self, node):
        print('Node type: BoolOp\nFields: ', node._fields)
        self.generic_visit(node)
    def visit_Name(self,node):
        print('Node type: Name\nFields: ', node._fields)
        ast.NodeVisitor.generic_visit(self, node)
visitor = BoolOpVisitor()
tree = ast.parse('a and b', mode='eval')
pprint(ast.dump(tree))
visitor.visit(tree)

Explanation

  • We define a BoolOpVisitor class that extends from the parent class ast.NodeVisitor. We override the predefined visit_BoolOp and visit_Name methods in the parent class, which receive the BoolOp 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 BoolOpVisitor.
  • We define a Python expression a and b and send it to the ast.parse() method with mode='eval', which returns the result of the expression after evaluation and stores it in tree.
  • The ast.dump() method returns a formatted string of the tree structure in tree.
  • The visit method available to the visitor objects visits all the nodes in the tree structure.

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