class_docstr: Utility class to represent and manipulate tags.
  Attributes:
      x:
          An integer representation of the binary mask.
  Examples:
      >>> # the following are equivalent
      >>> mask = BitMask(6)
      >>> mask = BitMask.from_hex('0x6')
      >>> mask = Bitmask.from_bin('0b0110')
      >>> # for a dataset with 10 images, assume the following tag
      >>> # 0001011001 where the 1st, 4th, 5th and 7th image are selected
      >>> # this tag would be stored as 0x59.
      >>> hexstring = '0x59'                    # what you receive from the api
      >>> mask = BitMask.from_hex(hexstring)  # create a bitmask from it
      >>> indices = mask.to_indices()         # get list of indices which are one
      >>> # indices is [0, 3, 4, 6]
docstr: Creates a all-true bitmask of a predefined length
docstr_tok: ["Creates","a","all-true","bitmask","of","a","predefined","length"]
code: def from_length(cls, length: int):
      """Creates a all-true bitmask of a predefined length"""
      binstring = "0b" + "1" * length
      return cls.from_bin(binstring)
  
imports: import copy
  from typing import List
label_desc: Use image node_id 4 for calling the BitMask obj's underlying member method code with example usage: obj.from_length(cls, length) and returns: cls