Python checking its own code before running (Usage Errors)

Question

I would like to build something into my Python module that can throw a warning if the user has not done something correctly. For example if the user has a while loop with nothing in it that will block threads, or a user does not initialize something correctly.

Currently I am loading the python file before it runs with a "pre-runtime" script to check these warnings. However it still requires the user to run this pre-check script. I would like to figure out how to do this in my main module. Aside from loading the python script as a string and then parsing it I can't think of a good way to do this.

For example if the user runs this code

import myModule
test = myModule.module()

print("Hello")

while 1:
    True

They would get

>> Warning, you used a print statement, they have no power here.

Or the alternative example in the other direction

import myModule
test = myModule.module()

They would get

>> Warning there is no while True loop, your code will just exit

Yes they will check normally errors that are pythonic. I am looking for special case handling related to this specific application. As a super basic example let's say I never want a user to use "print("hello")", again silly example but exactly the kind of case I am looking at. Python will not catch this as an error but in the context of my system it is an error. — Meozaa
– Meozaa, Commented Apr 23, 2021 at 12:37
if you are sure you are going to input a valid python code, something from docs.python.org/3/library/ast.html can help — python_user
– python_user, Commented Apr 23, 2021 at 12:42
BTW, edit your question elaborating exactly what you want, instead of in the comment section. — 12944qwerty
– 12944qwerty, Commented Apr 23, 2021 at 13:03

python_user · Accepted Answer · 2021-04-23 13:36:16Z

1

I am just writing this as a solution because I found this interesting, there may be better ways to accomplish.

check.py

import ast

with open('temp.py') as file:
    module_node = ast.parse(file.read())

for node in ast.walk(module_node):
    # check if there is `while True` loop
    if isinstance(node, ast.While) and isinstance(node.test, ast.Constant) and node.test.value is True:
        print('There is a `while True` in the code', node.lineno)

    # check if there is `print` call in the code
    elif isinstance(node, ast.Call) and node.func.id == 'print':
        print('There is a `print` call in the code', node.lineno)

temp.py

import foo # check.py does not run this import

while 1 > 2:
    while True:
        print('some text', '12321')

Output

There is a `while True` in the code 4
There is a `print` call in the code 5

So you get the idea, you just add in conditions in the for loop and have a message printed. Again, there may be better alternatives.

answered Apr 23, 2021 at 13:36

python_user

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2 Comments

Meozaa Over a year ago

Very cool, this is exactly the solution I was looking for. Thanks for pointing out ast, it is a very cool module. Then I can probably direct os.path.basename(__file__) to open the script automatically so the user doesn't have to import it. Solution found! Thanks!

python_user Over a year ago

glad to know this was helpful, can you mark this as accepted then @Meozaa?

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