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What is ast.alias(name, asname) in Python?

Abdul Monum
Abstract Syntax Tree

ast.alias(name, asname) is a class defined in the ast module that is used to express an aliassecond name for a piece of data 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 an alias, the ast.alias(name, asname) class is invoked, which expresses the alias to a node in an ast tree data structure. The ast.alias class represents the alias node type in the ast tree. In the class parameter, name, and asname contain raw strings of the names. If the as keyword is not used, then asname is None.

Example

import ast
from pprint import pprint

class AliasVisitor(ast.NodeVisitor):

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

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


visitor = AliasVisitor()
tree = ast.parse('import numpy as np')
pprint(ast.dump(tree))
visitor.visit(tree)

Explanation

  • We define an AliasVisitor class that extends from the parent class ast.NodeVisitor. We override the predefined visit_Import and visit_alias methods in the parent class, which receive the Import and alias 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 AliasVisitor.
  • We write the Python statement import numpy as np and send it to the ast.parse() method, which returns the result of the expression after evaluation, and store the result 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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