Checking if string contains valid Python code

Question

I am writing some sort of simple web-interpreter for vk.com . I look for messages, check if they are valid Python code, and then I want to execute that code, and return any stdout to code sender. I have implemented anything but code checker.

import ast
def is_valid(code): 
 try:
 ast.parse(code)
 except SyntaxError:
 print('Input isnt code.')
 return False
 print('Code is ok.')
 return True

is_valid() always return True regardless of what comes in. Im really confused...

• AChampion: Can you give an example of non-code that returns True.
• MaxLunar: >>> is_valid('test') Code is ok. True
• AChampion: That's valid code - an identifier.

Answer 1

Keep in mind, the difference between a runtime error and a parser error is significant in your case and example. The statement:

test

is valid code. Even though this statement will throw a NameError when the Python VM executes the code, the parser will not know that it actually wasn't assigned a value before the statement is parsed, so that's why it's a runtime error, and not a syntax error.

• MaxLunar: Thanks! Ill fix it by throwing NameError then
• Ryan: @MaxLunar you can't throw a NameError, because how would you know that the user's code is using a variable that wasn't assigned a value?
• Noufal Ibrahim: @MaxLunar I think you have a misunderstanding here. Is x + 1 valid code?
• MaxLunar: Hm, If i send message that tell user that his variable wasnt defined yet if NameError is raised...
• Noufal Ibrahim: @MaxLunar Why? What if x is not defined? Or if x is a string?