cyvcf2

Note: cyvcf2 versions < 0.20.0 require htslib < 1.10. cyvcf2 versions >= 0.20.0 require htslib >= 1.10

The latest documentation for cyvcf2 can be found here:

If you use cyvcf2, please cite the paper

Fast python (2 and 3) parsing of VCF and BCF including region-queries.

cyvcf2 is a cython wrapper around htslib built for fast parsing of Variant Call Format (VCF) files.

Attributes like variant.gt_ref_depths work for diploid samples and return a numpy array directly so they are immediately ready for downstream use. note that the array is backed by the underlying C data, so, once variant goes out of scope. The array will contain nonsense. To persist a copy, use: cpy = np.array(variant.gt_ref_depths) instead of just arr = variant.gt_ref_depths.

Example

The example below shows much of the use of cyvcf2.

from cyvcf2 import VCF

for variant in VCF('some.vcf.gz'): # or VCF('some.bcf')
    variant.REF, variant.ALT # e.g. REF='A', ALT=['C', 'T']

    variant.CHROM, variant.start, variant.end, variant.ID, \
                variant.FILTER, variant.QUAL

    # numpy arrays of specific things we pull from the sample fields.
    # gt_types is array of 0,1,2,3==HOM_REF, HET, UNKNOWN, HOM_ALT
    variant.gt_types, variant.gt_ref_depths, variant.gt_alt_depths # numpy arrays
    variant.gt_phases, variant.gt_quals, variant.gt_bases # numpy array

    ## INFO Field.
    ## extract from the info field by it's name:
    variant.INFO.get('DP') # int
    variant.INFO.get('FS') # float
    variant.INFO.get('AC') # float

    # convert back to a string.
    str(variant)


    ## sample info...

    # Get a numpy array of the depth per sample:
    dp = variant.format('DP')
    # or of any other format field:
    sb = variant.format('SB')
    assert sb.shape == (n_samples, 4) # 4-values per

# to do a region-query:

vcf = VCF('some.vcf.gz')
for v in vcf('11:435345-556565'):
    if v.INFO["AF"] > 0.1: continue
    print(str(v))

Installation

pip (assuming you have htslib < 1.10 installed)

pip install cyvcf2

github (building htslib and cyvcf2 from source)

git clone --recursive https://github.com/brentp/cyvcf2
cd cyvcf2/htslib
autoheader
autoconf
./configure --enable-libcurl
make

cd ..
pip install -r requirements.txt
CYTHONIZE=1 pip install -e .

On OSX, using brew, you may have to set the following as indicated by the brew install:

For compilers to find openssl you may need to set:
  export LDFLAGS="-L/usr/local/opt/openssl/lib"
  export CPPFLAGS="-I/usr/local/opt/openssl/include"

For pkg-config to find openssl you may need to set:
  export PKG_CONFIG_PATH="/usr/local/opt/openssl/lib/pkgconfig"

Testing

Install pytest, then tests can be run with:

pytest

CLI

Run with cyvcf2 path_to_vcf

$ cyvcf2 --help
Usage: cyvcf2 [OPTIONS] <vcf_file> or -

  fast vcf parsing with cython + htslib

Options:
  -c, --chrom TEXT                Specify what chromosome to include.
  -s, --start INTEGER             Specify the start of region.
  -e, --end INTEGER               Specify the end of the region.
  --include TEXT                  Specify what info field to include.
  --exclude TEXT                  Specify what info field to exclude.
  --loglevel [DEBUG|INFO|WARNING|ERROR|CRITICAL]
                                  Set the level of log output.  [default:
                                  INFO]
  --silent                        Skip printing of vcf.
  --help                          Show this message and exit.

Performance

For the performance comparison in the paper, we used thousand genomes chromosome 22 With the full comparison runner here.

brentp/cyvcf2

brentp

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