bedspec

An HTS-specs compliant BED toolkit.

Installation

The package can be installed with pip:

pip install bedspec

Quickstart

Building a BED Feature

>>> from bedspec import Bed3
>>> 
>>> bed = Bed3("chr1", start=2, end=8)

Records are checked against the BED spec when they are built. BED has no quoting, so text is written and read as it is, and a value holding a tab is refused. A feature may start where it ends, as an insertion does.

Records are immutable and hashable. Use dataclasses.replace to build a changed copy, which is checked like any other record:

>>> from dataclasses import replace
>>>
>>> replace(bed, end=10)
Bed3(refname='chr1', start=2, end=10)

Writing

>>> from bedspec import BedWriter
>>> from tempfile import NamedTemporaryFile
>>> 
>>> temp_file = NamedTemporaryFile(mode="w+t", suffix=".txt")
>>>
>>> with BedWriter.from_path[Bed3](temp_file.name) as writer:
...     writer.write(bed)

Reading

>>> from bedspec import BedReader
>>> 
>>> with BedReader.from_path[Bed3](temp_file.name) as reader:
...     for bed in reader:
...         print(bed)
Bed3(refname='chr1', start=2, end=8)

Compressed and Indexed BED

A path ending in .gz, .bgz, or .bgzf is written as BGZF, which any gzip reader can read, and a compressed file is read by its contents. Ask for a tabix or CSI index to have one written beside the file, with features sorted by reference and start.

>>> from pybgzf import IndexFormat
>>>
>>> with BedWriter.from_path[Bed3](f"{temp_file.name}.gz", index=IndexFormat.TBI, threads=4) as writer:
...     writer.write(Bed3("chr1", start=2, end=8))
...     writer.write(Bed3("chr1", start=6, end=9))
>>>
>>> with BedReader.from_path[Bed3](f"{temp_file.name}.gz") as reader:
...     print(list(reader))
[Bed3(refname='chr1', start=2, end=8), Bed3(refname='chr1', start=6, end=9)]

Query an indexed file on disk with the same operations as the overlap detector:

>>> from bedspec.overlap import TabixDetector
>>>
>>> with TabixDetector[Bed3](f"{temp_file.name}.gz") as detector:
...     print(list(detector.enclosing(Bed3("chr1", start=7, end=8))))
[Bed3(refname='chr1', start=2, end=8), Bed3(refname='chr1', start=6, end=9)]

No index query returns a zero-length feature at the start of a reference, so writing one to an indexed file warns.

BED Types

This package provides builtin classes for the following BED formats:

>>> from bedspec import Bed2
>>> from bedspec import Bed3
>>> from bedspec import Bed4
>>> from bedspec import Bed5
>>> from bedspec import Bed6
>>> from bedspec import Bed9
>>> from bedspec import Bed12
>>> from bedspec import BedGraph
>>> from bedspec import BedPE

It also provides the ENCODE peak formats:

>>> from bedspec import BroadPeak
>>> from bedspec import GappedPeak
>>> from bedspec import NarrowPeak

ENCODE writes -1 for a p-value, q-value, or summit that is not given, and so do these types.

For BED files with extra columns (BEDn+m), use Bed3N, Bed4N, Bed5N, Bed6N, Bed9N, or Bed12N. Each is its BED type plus an extra field that keeps any further columns as text.

>>> from bedspec import Bed6N
>>>
>>> _ = open(temp_file.name, "w").write("chr1\t5\t9\tpeak\t7\t-\t3.2\t0.01\n")
>>>
>>> with BedReader.from_path[Bed6N](temp_file.name) as reader:
...     for bed in reader:
...         print(bed.name, bed.extra)
peak ('3.2', '0.01')

Spans and Territory

Every BED record yields its pieces on reference sequences with spans(), each with its strand. A Bed2 yields its one base, a Bed3 to Bed9 yields itself, a BedPE yields both of its ends, and a Bed12 yields its blocks, so its introns are not part of it:

>>> from bedspec import BedStrand
>>>
>>> transcript = Bed12(
...     "chr1",
...     start=100,
...     end=200,
...     name="tx",
...     score=None,
...     strand=BedStrand.Positive,
...     thick_start=None,
...     thick_end=None,
...     item_rgb=None,
...     block_count=2,
...     block_sizes=(10, 20),
...     block_starts=(0, 80),
... )
>>> for span in transcript.spans():
...     print(span.refname, span.start, span.end, span.strand)
chr1 100 110 +
chr1 180 200 +

territory() returns the bases those spans hold, without their strands, as a Territory:

>>> transcript.territory()
Territory([Bed3(refname='chr1', start=100, end=110), Bed3(refname='chr1', start=180, end=200)])
>>> transcript.territory().length
30

Overlap Detection

Use a fast overlap detector for any collection of interval types, including third-party:

>>> from bedspec import Bed3, Bed4
>>> from bedspec.overlap import TreeDetector
>>>
>>> bed1 = Bed3("chr1", start=1, end=4)
>>> bed2 = Bed3("chr1", start=5, end=9)
>>> 
>>> detector = TreeDetector[Bed3]([bed1, bed2])
>>> 
>>> my_feature = Bed4("chr1", start=2, end=3, name="hi-mom")
>>> detector.overlaps(my_feature)
True

The overlap detector supports the following operations:

• overlapping: return all overlapping features
• overlaps: test if any overlapping features exist
• enclosed_by: return those enclosed by the input feature
• enclosing: return those enclosing the input feature

A zero-length feature overlaps the features that hold either base beside it.

A BED record is found by any of its spans(), so Bed2 points and BedPE pairs are supported, a BedPE is found by either end, and a Bed12 is found by its blocks. A query that touches only an intron of a Bed12 does not find it, so to find a Bed12 by its whole span, add it as a Bed6:

>>> intron = Bed3("chr1", start=150, end=160)
>>>
>>> list(TreeDetector[Bed12]([transcript]).overlapping(intron))
[]
>>> whole = Bed6(
...     transcript.refname,
...     start=transcript.start,
...     end=transcript.end,
...     name=transcript.name,
...     score=transcript.score,
...     strand=transcript.strand,
... )
>>> list(TreeDetector[Bed6]([whole]).overlapping(intron)) == [whole]
True

Each matching feature is returned once, even when several of its spans match. A feature encloses the input feature when any one of its spans does. A feature is enclosed by the input feature only when all of its spans are, so a BedPE needs both ends inside. Queries must be spans with an end, so a Bed2 can be added but cannot be used as a query. A TabixDetector answers every query the same way: its index finds each record by its whole extent, and each record found is then tested by its spans, so a query in an intron finds nothing there either.

Each operation takes stranded=True to find only features on the same strand as the query. For a BedPE, each end is compared by its own strand, and each block of a Bed12 by the record's strand. For the opposite strand, flip the query's strand with dataclasses.replace:

>>> from dataclasses import replace
>>> from bedspec import Bed6, BedStrand
>>>
>>> plus = Bed6("chr1", start=1, end=4, name=None, score=None, strand=BedStrand.Positive)
>>> minus = Bed6("chr1", start=1, end=4, name=None, score=None, strand=BedStrand.Negative)
>>> stranded = TreeDetector[Bed6]([plus, minus])
>>>
>>> list(stranded.overlapping(plus, stranded=True)) == [plus]
True
>>> list(stranded.overlapping(replace(plus, strand=plus.strand.opposite()), stranded=True)) == [minus]
True

Merging, Intersecting, and Subtracting

A Territory is the set of bases held by any number of spans and BED records, kept as the fewest spans that hold them. Spans that overlap or abut are joined, and a zero-length span holds no bases:

>>> from bedspec import Territory
>>>
>>> targets = Territory([
...     Bed3("chr1", start=0, end=10),
...     Bed3("chr1", start=5, end=20),
...     Bed3("chr1", start=20, end=30),
...     Bed3("chr2", start=0, end=5),
... ])
>>> list(targets)
[Bed3(refname='chr1', start=0, end=30), Bed3(refname='chr2', start=0, end=5)]
>>> targets.length
35

Territories combine like sets of bases, with | for the union, & for the intersection, and - for the difference. For example, the bases of the targets that a gene holds, less a mask of bases to ignore:

>>> gene = Territory([Bed3("chr1", start=25, end=40)])
>>> mask = Territory([Bed3("chr1", start=27, end=28)])
>>>
>>> share = (targets & gene) - mask
>>> share
Territory([Bed3(refname='chr1', start=25, end=27), Bed3(refname='chr1', start=28, end=30)])
>>> share.length
4

Test one base with contains, or whether every base of a span or BED record is held with in:

>>> share.contains("chr1", 26), share.contains("chr1", 27)
(True, False)
>>> Bed3("chr1", start=25, end=27) in share
True

A BED record adds every one of its spans, so a BedPE adds both of its ends and a Bed12 only its blocks, the same bases as its own territory(). Spans are yielded as Bed3 records, by start within each reference, with references in the order they were first added. Territories are immutable, hashable, and equal when they hold the same bases.

Custom BED Types

To create a custom BED record, inherit from the relevant BED-type (PointBed, SimpleBed, PairBed). Custom BED records must be frozen dataclasses too. A record of several pieces overrides spans() to yield them, and its territory() and overlap detection follow.

For example, to create a custom BED3+1 class:

>>> from dataclasses import dataclass
>>> 
>>> from bedspec import SimpleBed
>>> 
>>> @dataclass(frozen=True)
... class Bed3Plus1(SimpleBed):
...     refname: str
...     start: int
...     end: int
...     my_custom_field: float | None

You can also inherit and extend a pre-existing BED class:

>>> from dataclasses import dataclass
>>>
>>> from bedspec import Bed3
>>>
>>> @dataclass(frozen=True)
... class Bed3Plus1(Bed3):
...     my_custom_field: float | None
>>>
>>> Bed3Plus1(refname="chr1", start=2, end=3, my_custom_field=0.1)
Bed3Plus1(refname='chr1', start=2, end=3, my_custom_field=0.1)

Development and Testing

See the contributing guide for more information.