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# Copyright 2008-2015 by Peter Cock. All rights reserved.
#
# This file is part of the Biopython distribution and governed by your
# choice of the "Biopython License Agreement" or the "BSD 3-Clause License".
# Please see the LICENSE file that should have been included as part of this
# package.
"""Bio.SeqIO support for the "ace" file format.
You are expected to use this module via the Bio.SeqIO functions.
See also the Bio.Sequencing.Ace module which offers more than just accessing
the contig consensus sequences in an ACE file as SeqRecord objects.
"""
from Bio.Seq import Seq
from Bio.SeqRecord import SeqRecord
from Bio.Sequencing import Ace
def AceIterator(source):
"""Return SeqRecord objects from an ACE file.
This uses the Bio.Sequencing.Ace module to do the hard work. Note that
by iterating over the file in a single pass, we are forced to ignore any
WA, CT, RT or WR footer tags.
Ace files include the base quality for each position, which are taken
to be PHRED style scores. Just as if you had read in a FASTQ or QUAL file
using PHRED scores using Bio.SeqIO, these are stored in the SeqRecord's
letter_annotations dictionary under the "phred_quality" key.
>>> from Bio import SeqIO
>>> with open("Ace/consed_sample.ace") as handle:
... for record in SeqIO.parse(handle, "ace"):
... print("%s %s... %i" % (record.id, record.seq[:10], len(record)))
... print(max(record.letter_annotations["phred_quality"]))
Contig1 agccccgggc... 1475
90
However, ACE files do not include a base quality for any gaps in the
consensus sequence, and these are represented in Biopython with a quality
of zero. Using zero is perhaps misleading as there may be very strong
evidence to support the gap in the consensus. Previous versions of
Biopython therefore used None instead, but this complicated usage, and
prevented output of the gapped sequence as FASTQ format.
>>> from Bio import SeqIO
>>> with open("Ace/contig1.ace") as handle:
... for record in SeqIO.parse(handle, "ace"):
... print("%s ...%s..." % (record.id, record.seq[85:95]))
... print(record.letter_annotations["phred_quality"][85:95])
... print(max(record.letter_annotations["phred_quality"]))
Contig1 ...AGAGG-ATGC...
[57, 57, 54, 57, 57, 0, 57, 72, 72, 72]
90
Contig2 ...GAATTACTAT...
[68, 68, 68, 68, 68, 68, 68, 68, 68, 68]
90
"""
for ace_contig in Ace.parse(source):
# Convert the ACE contig record into a SeqRecord...
consensus_seq_str = ace_contig.sequence
if "*" in consensus_seq_str:
# For consistency with most other file formats, map
# any * gaps into - gaps.
assert "-" not in consensus_seq_str
consensus_seq = Seq(consensus_seq_str.replace("*", "-"))
else:
consensus_seq = Seq(consensus_seq_str)
# TODO? - Base segments (BS lines) which indicates which read
# phrap has chosen to be the consensus at a particular position.
# Perhaps as SeqFeature objects?
# TODO - Supporting reads (RD lines, plus perhaps QA and DS lines)
# Perhaps as SeqFeature objects?
seq_record = SeqRecord(consensus_seq, id=ace_contig.name, name=ace_contig.name)
# Consensus base quality (BQ lines). Note that any gaps (originally
# as * characters) in the consensus do not get a quality entry, so
# we assign a quality of None (zero would be misleading as there may
# be excellent support for having a gap here).
quals = []
i = 0
for base in consensus_seq:
if base == "-":
quals.append(0)
else:
quals.append(ace_contig.quality[i])
i += 1
assert i == len(ace_contig.quality)
seq_record.letter_annotations["phred_quality"] = quals
yield seq_record
# All done
if __name__ == "__main__":
from Bio._utils import run_doctest
run_doctest()
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