class_docstr: Create a new Frame that points to a dataframe in memory. All
  frames are stored in ``Frame.frames``. Names must be unique.
  
  Parameters
  ----------
  name : str
      Frame key.
  space : alphapy.Space
      Namespace of the given frame.
  df : pandas.DataFrame
      The contents of the actual dataframe.
  
  Attributes
  ----------
  frames : dict
      Class variable for storing all known frames
  
  Examples
  --------
  
  >>> Frame('tech', Space('stock', 'prices', '5m'), df)
code: def __str__(self):
      return frame_name(self.name, self.space)
  
file_path: AlphaPy/alphapy/frame.py
imports: from alphapy.globals import PSEP, SSEP, USEP
  from alphapy.globals import TAG_ID
  import logging
  import pandas
label_desc: Use image node_id 2 for calling the Frame obj's underlying member method code with example usage: obj.__str__() and returns: frame_name