How can you find unused functions in Python code?

In Python you can find unused code by using dynamic or static code analyzers. Two examples for dynamic analyzers are coverage and figleaf. They have the drawback that you have to run all possible branches of your code in order to find unused parts, but they also have the advantage that you get very reliable results.

Alternatively, you can use static code analyzers that just look at your code, but don't actually run it. They run much faster, but due to Python's dynamic nature the results may contain false positives.
Two tools in this category are pyflakes and vulture. Pyflakes finds unused imports and unused local variables. Vulture finds all kinds of unused and unreachable code. (Full disclosure: I'm the maintainer of Vulture.)

The tools are available in the Python Package Index https://pypi.org/.

Get all the unused variables in a Python project

Use pylint!

Install it with

pip install pylint

And run it on your project files

find . -name "*.py" | xargs pylint

The above command will find all Python source files in your project and feed them using xargs to pylint. Pylint with output a report containing all lint warnings including unused variables.

Remove unused variables in Python source code

The solution below works in two parts. First, the syntax tree of the source is traversed and all unused target assignment statements are discovered. Second, the tree is traversed again via a custom ast.NodeTransformer class, which removes these offending assignment statements. The process is repeated until all unused assignment statements are removed. Once this is finished, the final source is written out.

The ast traverser class:

import ast, itertools, collections as cl
class AssgnCheck:
   def __init__(self, scopes = None):
      self.scopes = scopes or cl.defaultdict(list)
   @classmethod
   def eq_ast(cls, a1, a2):
      #check that two `ast`s are the same
      if type(a1) != type(a2):
         return False
      if isinstance(a1, list):
         return all(cls.eq_ast(*i) for i in itertools.zip_longest(a1, a2))
      if not isinstance(a1, ast.AST):
         return a1 == a2
      return all(cls.eq_ast(getattr(a1, i, None), getattr(a2, i, None)) 
                 for i in set(a1._fields)|set(a2._fields) if i != 'ctx')
   def check_exist(self, t_ast, s_path):
      #traverse the scope stack and remove scope assignments that are discovered in the `ast`
      s_scopes = []
      for _ast in t_ast:
         for sid in s_path[::-1]:
            s_scopes.extend(found:=[b for _, b in self.scopes[sid] if AssgnCheck.eq_ast(_ast, b) and \
                all(not AssgnCheck.eq_ast(j, b) for j in s_scopes)])
            self.scopes[sid] = [(a, b) for a, b in self.scopes[sid] if b not in found]
   def traverse(self, _ast, s_path = [1]):
      #walk the ast object itself
      _t_ast = None
      if isinstance(_ast, ast.Assign): #if assignment statement, add ast object to current scope
         self.traverse(_ast.targets[0], s_path)
         self.scopes[s_path[-1]].append((True, _ast.targets[0]))
         _ast = _ast.value
      if isinstance(_ast, (ast.ClassDef, ast.FunctionDef, ast.AsyncFunctionDef)):
         s_path = [*s_path, (nid:=(1 if not self.scopes else max(self.scopes)+1))]
         if isinstance(_ast, (ast.FunctionDef, ast.AsyncFunctionDef)):
            self.scopes[nid].extend([(False, ast.Name(i.arg)) for i in _ast.args.args])
            _t_ast = [*_ast.args.defaults, *_ast.body]
      self.check_exist(_t_ast if _t_ast is not None else [_ast], s_path) #determine if any assignment statement targets have previously defined names
      if _t_ast is None:
         for _b in _ast._fields:
            if isinstance((b:=getattr(_ast, _b)), list):
               for i in b:
                  self.traverse(i, s_path)
            elif isinstance(b, ast.AST):
               self.traverse(b, s_path)
      else:
          for _ast in _t_ast:
             self.traverse(_ast, s_path)
         

---

Putting it all together:

class Visit(ast.NodeTransformer):
   def __init__(self, asgn):
       super().__init__()
       self.asgn = asgn
   def visit_Assign(self, node):
       #remove assignment nodes marked as unused
       if any(node.targets[0] == i for i in self.asgn):
          return None
       return node

def remove_assgn(f_name):
  tree = ast.parse(open(f_name).read())
  while True:
     r = AssgnCheck()
     r.traverse(tree)
     if not (k:=[j for b in r.scopes.values() for k, j in b if k]):
        break
     v = Visit(k)
     tree = v.visit(tree)
  return ast.unparse(tree)

print(remove_assgn('test_name_assign.py'))

---

Output Samples

Contents of test_name_assign.py:

def hailstone_sequence(n: int) -> Iterable[int]:
    while n != 1:
        if 0 == n % 2:
            n //= 2
            _hy_anon_var_1 = None
        else:
            n = 3 * n + 1
            _hy_anon_var_1 = None
        yield n

Output:

def hailstone_sequence(n: int) -> Iterable[int]:
    while n != 1:
        if 0 == n % 2:
            n //= 2
        else:
            n = 3 * n + 1
        yield n

---

Contents of test_name_assign.py:

def h():
    _hyx_letXUffffX25 = {}
    _hyx_letXUffffX25['x'] = 5
    return 3

Output:

def h():
    return 3

---

Contents of test_name_assign.py:

def f():
    i = 0
    return 5

Output:

def f():
    return 5

---

Contents of test_name_assign.py:

def f():
    x = 10
    def g():
        return x/5
    return g(100)

Ouptut:

def f():
    x = 10
    def g():
        return x / 5
    return g(100)

---

Related Topics