pysam

To compute per-base coverage from a BAM file, fetch reads by genomic region and run pileup-style analyses for read depth. This requires an indexed BAM file to enable random-access queries over target intervals.

Yes, you can query VCF variants by genomic coordinate to iterate variants, inspect INFO/FORMAT fields, and extract genotypes. The VariantFile interface supports subsetting VCF/BCF files for downstream analysis.

Extract reference sequences by coordinate from a FASTA file using random-access support. The FastaFile interface enables targeted sequence extraction, while FASTQ records can be streamed for quality control and read filtering.

Incorrect region query coordinates often result from mismatched coordinate handling between 0-based half-open intervals and 1-based samtools region strings. Correct coordinate handling is required for accurate SAM/BAM/CRAM alignment parsing.

The best way to validate variants and annotate coverage in bioinformatics pipelines is to combine BAM, VCF, and FASTA workflows. This integrated approach validates variants, annotates with depth (DP), and extracts sequence contexts.

Yes, pysam requires indexed files to support random-access queries on CRAM alignments and other NGS formats. Indexed random-access support is necessary for fetching reads by genomic region and running pileup analyses.