How to find/detect if a build-in function is used in Python AST?

Question

The goal is to detect if a builtin function such as eval() is used in some code.

def foo(a):
    eval('a = 2')

I have tried the following approach:

ex_ast = ast.parse(inspect.getsource(foo))

for node in ast.walk(ex_ast):
if isinstance(node, ast.FunctionDef):
    print(node.name)

The function name foo is printed as the output.

I know that Builtin functions don't have constructors. They are in the type Module. So 1 approach would be using types.FunctionType in an isinstance call.

But since I'm using AST nodes. They cannot be transformed back into code. I have to check for each node if they are types.FunctionType :

for node in ast.walk(ex_ast):
    if isinstance(node, ast.FunctionType):
        print(node.name)

I got these errors:

AttributeError: module 'ast' has no attribute 'FunctionType'

How should I correctly identify if a specific Buildin Function is used in code? Thanks!

Answer 1

When you write eval(whatever) in your code, eval is looked up by an ordinary global variable lookup. You should look for an ast.Name node representing a use of the variable name eval :

for node in ast.walk(ex_ast):
    if isinstance(node, ast.Name) and node.id == 'eval':
        # Found it.

Since you have an actual function object, not just the source code, you can also check for variables that shadow the built-in in a slightly more reliable manner than if you just had the function's source:

if ('eval' in foo.__code__.co_varnames     # local variable
    or 'eval' in foo.__code__.co_cellvars  # local variable used by nested function
    or 'eval' in foo.__code__.co_freevars  # local variable from enclosing function
    or 'eval' in foo.__globals__):         # global variable
    # Some variable is shadowing the built-in.

This won't catch globals added after the check, and it won't do anything about accesses to the built-in by a different name (for example, x = eval; x('whatever') ). Whether it's worthwhile is up to you.