What is ast.Import(names) in Python?

Abstract Syntax Tree

ast.Import(names) is a class defined in the ast module that is used to express the import 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 import keyword, the ast.Import class is invoked, which expresses the import statement to a node in an ast tree data structure.

The ast.Import class represents the Import node type in the ast tree. In the class parameter, names contains the list of alias nodes representing modules that need to be imported.

Note: If the import statement is preceded by the from keyword, then ast.ImportFrom class is invoked instead.

Example

import ast
from pprint import pprint
class ImportVisitor(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 = ImportVisitor()
tree = ast.parse('import socket, threading')
pprint(ast.dump(tree))
visitor.visit(tree)

Explanation

  • We define a ImportVisitor 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 ImportVisitor.
  • We write the Python statement import socket, threading and send it to the ast.parse() method, which returns the result of the expression after evaluation, and 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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