input: Write a function to detect any potential errors in the given Python function. The function should analyze the `expand_list` function and return a string explaining the potential error and how to fix it. If there is no error, the function should return an empty string. 
  
  def detect_errors(func):
      func_code = func.__code__
      for_idx = func_code.co_names.index('for')
      in_idx = func_code.co_names.index('in')
      iterating_list = func_code.co_varnames[in_idx - for_idx]
      modifying_list = func_code.co_varnames[for_idx - in_idx]
      if iterating_list == modifying_list:
          return f"The function is attempting to modify the {modifying_list} while iterating over it. This can lead to unexpected behavior and should be avoided. To fix the code, the list should be copied before the iteration takes place."
      return ""
  
  assert detect_errors(expand_list) == "The function is attempting to modify the list while iterating over it. This can lead to unexpected behavior and should be avoided. To fix the code, the list should be copied before the iteration takes place."
  assert detect_errors(lambda l: [l.append(x) for x in l]) == "The function is attempting to modify the l while iterating over it. This can lead to unexpected behavior and should be avoided. To fix the code, the list should be copied before the iteration takes place."
  assert detect_errors(lambda l: l) == ""
output: 
  def detect_errors(func):
      func_code = func.__code__
      for_idx = func_code.co_names.index('for')
      in_idx = func_code.co_names.index('in')
      iterating_list = func_code.co_varnames[in_idx - for_idx]
      modifying_list = func_code.co_varnames[for_idx - in_idx]
      if iterating_list == modifying_list:
          return f"The function is attempting to modify the {modifying_list} while iterating over it. This can lead to unexpected behavior and should be avoided. To fix the code, the list should be copied before the iteration takes place."
      return ""
  