modify_ast_binop.py

import ast


class CrazyTransformer(ast.NodeTransformer):
    def visit_BinOp(self, node):
        print(node.__dict__)
        node.op = ast.Mult()
        print(node.__dict__)
        return node


expr = """
def add(arg1, arg2):
    return arg1 + arg2
print(add(4, 5))
"""
expr_ast = ast.parse(expr)

transformer = CrazyTransformer()
unmodified = ast.parse(expr)
exec(compile(unmodified, '<string>', 'exec'))
modified = transformer.visit(expr_ast)
exec(compile(modified, '<string>', 'exec'))

s = "print('hello, world')"
s_ast = ast.parse(s)
new_ast = ast.parse(s)
new_ast.body[0].value.args[0].s = "hello, hank"
exec(compile(s_ast, 'string', 'exec'))
exec(compile(new_ast, 'string', 'exec'))

modify_code_co_consts.py

from types import CodeType

s = "print('hello, world')"
c = compile(s, 'test.py', 'exec')
exec(c)

new_co_consts = ('hello, hank', None)
new_c = CodeType(c.co_argcount, c.co_kwonlyargcount, c.co_nlocals, c.co_stacksize, c.co_flags, c.co_code,
                 new_co_consts, c.co_names, c.co_varnames, c.co_filename, c.co_name, c.co_firstlineno,
                 c.co_lnotab, c.co_freevars, c.co_cellvars)
exec(new_c)

modify_code_object.py

from types import CodeType

expr = """
def add(arg1, arg2):
    return arg1 + arg2
print(add(4, 5))
"""
patch = """
def multi(a, b):
    return a * b
"""
expr_code = compile(expr, '<string>', 'exec')
patch_code = compile(patch, '<string>', 'exec')
new_co_consts = expr_code.co_consts
new_co_consts = (patch_code.co_consts[0],) + expr_code.co_consts[1:]
new_c = CodeType(expr_code.co_argcount,
                 expr_code.co_kwonlyargcount,
                 expr_code.co_nlocals,
                 expr_code.co_stacksize,
                 expr_code.co_flags,
                 expr_code.co_code,
                 new_co_consts,
                 expr_code.co_names,
                 expr_code.co_varnames,
                 expr_code.co_filename,
                 expr_code.co_name,
                 expr_code.co_firstlineno,
                 expr_code.co_lnotab,
                 expr_code.co_freevars,
                 expr_code.co_cellvars
                 )
exec(expr_code)
exec(new_c)