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What is ast.ExceptHandler(type, name, body) in Python?
Abdul Monum
ast.ExceptHandler is a class defined in the ast module that expresses the except clause in Python in the form of an Abstract Syntax Tree. When the parse() method of ast is called on Python source code that contains an except clause, the ast.ExceptHandler class is invoked, which expresses the except clause to a node in an ast tree data structure. The ast.ExceptHandler class represents the ExcpetHandler node type in the ast tree.
Class parameters
type: the exception type that is matched.typeis typically aNamenode.name: a raw string that contains the name of the exception or aNonenode if no name is specified.body: list of nodes in theexceptblock.
Code
import ast
from pprint import pprint
class ExceptHandlerVisitor(ast.NodeVisitor):
def visit_Try(self, node):
print('Node type: Try\nFields:', node._fields)
ast.NodeVisitor.generic_visit(self, node)
def visit_ExceptHandler(self, node):
print('Node type: ExceptHandler\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)
def visit_Pass(self, node):
print('Node type: Pass\nFields:', node._fields)
ast.NodeVisitor.generic_visit(self, node)
visitor = ExceptHandlerVisitor()
tree = ast.parse("""
try:
pass
except TypeError:
pass
else:
pass
finally:
pass
""")
pprint(ast.dump(tree))
visitor.visit(tree)Explanation
- We define a
ExceptHandlerVisitorclass that extends from the parent classast.NodeVisitor. We override the predefinedvisit_Try,visit_ExceptHandler,visit_Name, andvisit_Passmethods in the parent class, which receive theTry,ExceptHandler,Name, andPassnodes, respectively. In the method, we print the type and the fields inside the node and call thegeneric_visit()method, which invokes the propagation of visit on the children nodes of the input node. - We initialize a visitor object of the class
ExceptHandlerVisitor. - We write Python code that contains a
tryandexceptblock. We pass the code to theast.parse()method, which returns the result of the expression after evaluation and store the result in a tree. - The
ast.dump()method returns a formatted string of the tree structure in a tree. - The
visitmethod available to the visitor object visits all the nodes in the tree structure.
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