Checks for cases when you rewrite loop variable with inner loop
    for i in xrange(5):
      for i in xrange(20, 25):
          print("Inner", i)
      print("Outer", i)
  
It also warns you if variable declared in with statement is redeclared inside of statement body:
    with open("file") as f:
      f.read()
      with open("file") as f: