What is ast.Nonlocal(names) in Python?
Python ast module
The ast module (where ast stands for
This module helps applications to process trees of syntax and find out what the current syntax grammar looks like programmatically. Abstract syntax trees are great tools for program analysis and program transformation systems.
The ast.Nonlocal method
ast.Nonlocal(names) is a class defined in the ast module that expresses a nonlocal statement in Python in the form of an Abstract Syntax Tree.
When the parse() method of ast is called on a Python source code that contains nonlocal statements, the ast.Nonlocal class is invoked. This expresses the nonlocal statement to a node in an ast tree data structure. The ast.Nonlocal class represents the Nonlocal node type in the ast tree.
Parameters
names: A list of raw strings.
Example
The following Python code illustrates an example of the ast.Nonlocal class.
import ast
from pprint import pprint
class NonlocalVisitor(ast.NodeVisitor):
def visit_Nonlocal(self, node):
print('Node type: Nonlocal\nFields: ', node._fields)
self.generic_visit(node)
visitor = NonlocalVisitor()
tree = ast.parse("""
nonlocal a,b,c
""")
pprint(ast.dump(tree))
visitor.visit(tree)Code description
- We define a
NonlocalVisitorclass that extends from theast.NodeVisitorparent class. We override the predefinedvisit_Nonlocalmethod in the parent class, which receives theNonlocalnode. - In these methods, we print the type and the fields inside the node and call the
generic_visit()method to visit the children nodes of the input node. - We initialize a visitor object of the class
NonlocalVisitorin line 18. - We write a
nonlocalstatement in Python and send it to theast.parse()method, which returns the result of the expression after evaluation, and then stores this result intree. - The
ast.dump()method returns a formatted string of the tree structure intree. You can observe the string returned by thedumpfunction in the output of the code. - The inbuilt
visitmethod available to thevisitorobject visits all the nodes in the tree structure.
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