[issue42889] Incorrect behavior of Python parser after ast node of test program being modified

[Xinmeng Xia]

Xinmeng Xia <xiaxm at smail.nju.edu.cn> added the comment:

Sorry, my description is a little confusing. My points lie on function 'compile' and 'exec'. Yes, I agree. AST can be modified and don't correspond to valid programs.  But I don't think this invaild program can be compiled and exec without any check. It's dangerous.  

See the following program: For "compile" and "exec", no error is reported on Python 3.5-3.8 while error messages are reported on Python 3.9 and 3.10

======================================
import ast
class RewriteName(ast.NodeTransformer):
    def visit_Name(self, node):
        if node.id != "print":
            node.id = str(False)
            print(type(node.id))
        return node

code = "a = 2;print(a)"

myast = ast.parse(code)
transformer = RewriteName()
newast = transformer.visit(myast)

c = compile(newast,'','exec')
exec(c)
=====================================
Error message on Python 3.9  and 3.10.
-------------------------------------
<class 'str'>
<class 'str'>
Traceback (most recent call last):
  File "/home/xxm/Desktop/nameChanging/report/test1.py", line 574, in <module>
    c = compile(newast,'','exec')
ValueError: Name node can't be used with 'False' constant
-------------------------------------

In fact, in class RewriteName, when "node.id" is assigned, the parser will check whether the identifier is a "str". If not,"TypeError: AST identifier must be of type str" will be reported. However, it's not enough. In Python, identifier names have their own naming rules.  "str" could be "+","1","False", but these are not legally id. So the above error could be reported.

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue42889>
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