Comment lines are allowed at the top of the file. Usually comments start with a '#' but sometimes with a ';' character. The fmt properties allow configuring which is allowed during parsing and printing.
Description lines begin with the '>' character. Various conventions are used for the content but there is no requirement. We simply return the string following the '>' character.
Sequences are most often a sequence of characters denoting nucleotides or amino acids, and thus an item's sequence field is set to a string. Sequences may span multiple lines.
However, sequence lines sometimes are used to provide quality scores, either as space separated integers or as ASCII encoded scores. To support the former case, we provide the sequence_to_int_list function. For the latter case, see modules Phred_score and Solexa_score.
FASTA files are used to provide both short sequences and very big sequences, e.g. a genome. In the latter case, the main API of this module, which returns each sequence as an in-memory string, might be too costly. Consider using instead the Parser0 module which does not merge multiple sequence lines into one string. This API is slightly more difficult to use but perhaps a worthwhile trade-off.
Format Specifiers:
Variations in the format are controlled by the following settings, all of which have a default value. These properties are combined into the fmt type for convenience and the defaults into default_fmt.
allow_sharp_comments: Allow comment lines beginning with a '#' character. Default: true.
allow_semicolon_comments: Allow comment lines beginning with a ';' character. Default: false.
Setting both allow_sharp_comments and allow_semicolon_comments allows both. Setting both to false disallows comment lines.
allow_empty_lines: Allow lines with only whitespace anywhere in the file. Default: false.
max_line_length: Require sequence lines to be shorter than given length. None means there is no restriction. Note this does not restrict the length of an item's sequence field because this can span multiple lines. Default: None.
alphabet: Require sequence characters to be at most those in given string. None means any character is allowed. Default: None.