The training options for the spm_train can be listed using spm_train --help. Since the standard pip install of sentencepiece does not necessarily install spm_train, the options are also listed here.
--help (show help) type: bool default: false
--version (show version) type: bool default: false
--minloglevel (Messages logged at a lower level than this don't actually get logged anywhere) type: int default: 0
--input (comma separated list of input sentences) type: std::string default: ""
--input_format (Input format. Supported format is `text` or `tsv`.) type: std::string default: ""
--model_prefix (output model prefix) type: std::string default: "" --model_type (model algorithm: unigram, bpe, word or char) type: std::string default: "unigram"
--vocab_size (vocabulary size) type: int32 default: 8000
--accept_language (comma-separated list of languages this model can accept) type: std::string default: ""
--self_test_sample_size (the size of self test samples) type: int32 default: 0
--character_coverage (character coverage to determine the minimum symbols) type: double default: 0.9995
--input_sentence_size (maximum size of sentences the trainer loads) type: int32 default: 0
--shuffle_input_sentence (Randomly sample input sentences in advance. Valid when --input_sentence_size > 0) type: bool default: true
--seed_sentencepiece_size (the size of seed sentencepieces) type: int32 default: 1000000
--shrinking_factor (Keeps top shrinking_factor pieces with respect to the loss) type: double default: 0.75
--num_threads (number of threads for training) type: int32 default: 16
--num_sub_iterations (number of EM sub-iterations) type: int32 default: 2
--max_sentencepiece_length (maximum length of sentence piece) type: int32 default: 16
--max_sentence_length (maximum length of sentence in byte) type: int32 default: 4192
--split_by_unicode_script (use Unicode script to split sentence pieces) type: bool default: true
--split_by_number (split tokens by numbers (0-9)) type: bool default: true
--split_by_whitespace (use a white space to split sentence pieces) type: bool default: true
--split_digits (split all digits (0-9) into separate pieces) type: bool default: false
--treat_whitespace_as_suffix (treat whitespace marker as suffix instead of prefix.) type: bool default: false
--control_symbols (comma separated list of control symbols) type: std::string default: ""
--user_defined_symbols (comma separated list of user defined symbols) type: std::string default: ""
--required_chars (UTF8 characters in this flag are always used in the character set regardless of --character_coverage) type: std::string default: ""
--byte_fallback (decompose unknown pieces into UTF-8 byte pieces) type: bool default: false
--vocabulary_output_piece_score (Define score in vocab file) type: bool default: true
--normalization_rule_name (Normalization rule name. Choose from nfkc or identity) type: std::string default: "nmt_nfkc"
--normalization_rule_tsv (Normalization rule TSV file. ) type: std::string default: ""
--denormalization_rule_tsv (Denormalization rule TSV file.) type: std::string default: ""
--add_dummy_prefix (Add dummy whitespace at the beginning of text) type: bool default: true
--remove_extra_whitespaces (Removes leading, trailing, and duplicate internal whitespace) type: bool default: true
--hard_vocab_limit (If set to false, --vocab_size is considered as a soft limit.) type: bool default: true
--use_all_vocab (If set to true, use all tokens as vocab. Valid for word/char models.) type: bool default: false
--unk_id (Override UNK (<unk>) id.) type: int32 default: 0
--bos_id (Override BOS (<s>) id. Set -1 to disable BOS.) type: int32 default: 1
--eos_id (Override EOS (</s>) id. Set -1 to disable EOS.) type: int32 default: 2
--pad_id (Override PAD (<pad>) id. Set -1 to disable PAD.) type: int32 default: -1
--unk_piece (Override UNK (<unk>) piece.) type: std::string default: "<unk>"
--bos_piece (Override BOS (<s>) piece.) type: std::string default: "<s>"
--eos_piece (Override EOS (</s>) piece.) type: std::string default: "</s>"
--pad_piece (Override PAD (<pad>) piece.) type: std::string default: "<pad>"
--unk_surface (Dummy surface string for <unk>. In decoding <unk> is decoded to `unk_surface`.) type: std::string default: " ⁇ "
--train_extremely_large_corpus (Increase bit depth for unigram tokenization.) type: bool default: false