<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def declares_namespace_package(filename):
 """Given a filename, walk its ast and determine if it declares a namespace package."""


  import ast

  with open(filename) as fp:
    init_py = ast.parse(fp.read(), filename)
  calls = [node for node in ast.walk(init_py) if isinstance(node, ast.Call)]
  for call in calls:
    if len(call.args) != 1:
      continue
    if isinstance(call.func, ast.Attribute) and call.func.attr != 'declare_namespace':
      continue
    if isinstance(call.func, ast.Name) and call.func.id != 'declare_namespace':
      continue
    if isinstance(call.args[0], ast.Name) and call.args[0].id == '__name__':
      return True
  return False