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...

Can you give an example of non-code that returns True.

AChampion
– AChampion

2016-10-04 04:51:43 +00:00
Commented Oct 4, 2016 at 4:51 — AChampion
– AChampion, Commented Oct 4, 2016 at 4:51
>>> is_valid('test') Code is ok. True

MaxLunar
– MaxLunar

2016-10-04 04:56:51 +00:00
Commented Oct 4, 2016 at 4:56 — MaxLunar
– MaxLunar, Commented Oct 4, 2016 at 4:56
That's valid code - an identifier.

AChampion
– AChampion

2016-10-04 04:57:43 +00:00
Commented Oct 4, 2016 at 4:57 — AChampion
– AChampion, Commented Oct 4, 2016 at 4:57

Ryan · Accepted Answer · 2016-10-04 05:00:13Z

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.

edited Oct 4, 2016 at 5:00

answered Oct 4, 2016 at 4:54

Ryan

14.7k9 gold badges68 silver badges104 bronze badges

Sign up to request clarification or add additional context in comments.

6 Comments

MaxLunar Over a year ago

Thanks! Ill fix it by throwing NameError then

Ryan Over a year ago

@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 Over a year ago

@MaxLunar I think you have a misunderstanding here. Is x + 1 valid code?

MaxLunar Over a year ago

Hm, If i send message that tell user that his variable wasnt defined yet if NameError is raised...

Noufal Ibrahim Over a year ago

@MaxLunar Why? What if x is not defined? Or if x is a string?

|

Collectives™ on Stack Overflow

Checking if string contains valid Python code

1 Answer 1

6 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

6 Comments

Your Answer

Sign up or log in

Post as a guest

Related