class_docstr: Writer of UCI format for :class:`gensim.corpora.ucicorpus.UciCorpus`.
  
  Notes
  ---------
  This corpus format is identical to `Matrix Market format<http://math.nist.gov/MatrixMarket/formats.html>,
  except for different file headers. There is no format line, and the first three lines of the file
  contain `number_docs`, `num_terms`, and `num_nnz`, one value per line.
docstr: Write blank header lines. Will be updated later, once corpus stats are known.
docstr_tok: ["Write","blank","header","lines",".","Will","be","updated","later",",","once","corpus","stats","are","known","."]
code: def write_headers(self):
      """Write blank header lines. Will be updated later, once corpus stats are known."""
      for _ in range(3):
          self.fout.write(self.FAKE_HEADER)
  
      self.last_docno = -1
      self.headers_written = True
  
imports: import logging
  from collections import defaultdict
  from gensim import utils
  from gensim.corpora import Dictionary
  from gensim.corpora import IndexedCorpus
  from gensim.matutils import MmReader
  from gensim.matutils import MmWriter
label_desc: Use image node_id 1 for calling the UciWriter obj's underlying member method code with example usage: obj.write_headers() without return types