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Annotates a Python AST with the scope of symbols.

Project description


This package is an implementation of Python's lexical scoping rules. It's interface is simple, you pass in an AST object to the annotate function, and it provides a mapping from each node in the tree that represents a symbol to the containing scope.

Example Usage: Get Global Symbols

Let's say you have the code

code = """
def f():
    x = 3
    lambda z: theta
    return x + y

and you want to determine which global variables are referenced by it. All you need to do is run

import ast
import ast_scope
tree = ast.parse(code)
scope_info = ast_scope.annotate(tree)
global_variables = sorted(scope_info.global_scope.symbols_in_frame)

Once you have executed this code, global_variables will be bound to ['f', 'theta', 'y'].

Example Usage: Get Dependency Graph

Let's say you have the code

code = """
def hailstone(n):
    if n == 1:
        return 1
    if n % 2 == 0:
        return hailstone(n // 2)
    if n % 2 == 1:
        return hailstone(3 * n + 1)

def mapper(f, lst):
    return list(map(f, lst))

def lrange(n):
    return list(range(n))

def main():
    return mapper(hailstone, lrange(20))

and you want to find the dependency graph. You can run

import ast
import ast_scope
tree = ast.parse(code)
scope_info = ast_scope.annotate(tree)
graph = scope_info.static_dependency_graph

which results in the following directed graph of dependencies between top-level functions (rendering using networkx):

See the documentation for some caveats.

Example usage: find a specific symbol's scope

Take the following code:

code = """
def f(x):
    def g(x): return x()
    return g(lambda: x)

First, parse the code and identify the node (in practice, you'd probably have this always).

import ast, ast_scope
tree = ast.parse(code)
last_x = tree.body[0].body[-1].value.args[0].body

If you want to find the scope in which the last x could be found, just run the annotator and look up it's scope!

# run the annotator
scope_info = ast_scope.annotate(tree)
scope_x = scope_info[last_x]

You should get a FunctionScope object which contains a bunch of information about the other variables, etc., in the scope, but also scope_x.function_node, a pointer to the node containing the def statement for f.

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