biopython

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# Biopython: Computational Molecular Biology in Python

## Overview

Biopython is a comprehensive set of freely available Python tools for biological computation. It provides functionality for sequence manipulation, file I/O, database access, structural bioinformatics, phylogenetics, and many other bioinformatics tasks. These examples target **Biopython 1.88** (released 6 August 2026), tested here on Python 3.13. It requires Python 3.10+ and NumPy; Python 3.10 support is deprecated. Upgrade to 1.88 for its `Bio.Nexus` parser security fix, in addition to the Entrez XML fix in 1.87. See the [release notes](https://github.com/biopython/biopython/blob/biopython-188/NEWS.rst). Local example checks and external-service limits are recorded in `references/review.md`; examples requiring user files or external programs are illustrative unless listed there as exercised.

## When to Use This Skill

Use this skill when:

- Working with biological sequences (DNA, RNA, or protein)
- Reading, writing, or converting biological file formats (FASTA, GenBank, FASTQ, PDB, mmCIF, etc.)
- Accessing NCBI databases (GenBank, PubMed, Protein, Gene, etc.) via Entrez
- Running BLAST searches or parsing BLAST results
- Performing sequence alignments (pairwise or multiple sequence alignments)
- Analyzing protein structures from PDB files
- Creating, manipulating, or visualizing phylogenetic trees
- Finding sequence motifs or analyzing motif patterns
- Calculating sequence statistics (GC content, molecular weight, melting temperature, etc.)
- Performing structural bioinformatics tasks
- Working with population genetics data
- Any other computational molecular biology task

## Core Capabilities

Biopython is organized into modular sub-packages, each addressing specific bioinformatics domains:

1. **Sequence Handling** - Bio.Seq and Bio.SeqIO for sequence manipulation and file I/O
2. **Alignment Analysis** - Bio.Align and Bio.AlignIO for pairwise and multiple sequence alignments
3. **Database Access** - Bio.Entrez for programmatic access to NCBI databases
4. **BLAST Operations** - Bio.Blast for running and parsing BLAST searches
5. **Structural Bioinformatics** - Bio.PDB for working with 3D protein structures
6. **Phylogenetics** - Bio.Phylo for phylogenetic tree manipulation and visualization
7. **Advanced Features** - Motifs, population genetics, sequence utilities, and more

## Installation and Setup

Install the current stable Biopython release with an explicit version pin for reproducibility:

```bash
uv pip install "biopython==1.88"
```

For NCBI database access, always set your email address (required by NCBI). For reusable software, set a stable `Entrez.tool` value and register the tool/email with NCBI. For higher rate limits (10 req/s instead of 3 req/s), read only `NCBI_API_KEY` from the environment — do not hardcode keys or load unrelated environment variables:

```python
import os
from Bio import Entrez

Entrez.email = "your.email@example.com"  # required — use your real email
Entrez.tool = "your_tool_name"  # optional but recommended for reusable software

# Optional: register at https://www.ncbi.nlm.nih.gov/account/settings/
if api_key := os.environ.get("NCBI_API_KEY"):
    Entrez.api_key = api_key
```

## Using This Skill

This skill provides comprehensive documentation organized by functionality area. When working on a task, consult the relevant reference documentation:

### 1. Sequence Handling (Bio.Seq & Bio.SeqIO)

**Reference:** `references/sequence_io.md`

Use for:
- Creating and manipulating biological sequences
- Reading and writing sequence files (FASTA, GenBank, FASTQ, etc.)
- Converting between file formats
- Extracting sequences from large files
- Sequence translation, transcription, and reverse complement
- Working with SeqRecord objects

**Quick example:**
```python
from Bio import SeqIO

# Read sequences from FASTA file
for record in SeqIO.parse("sequences.fasta", "fasta"):
    print(f"{record.id}: {len(record.seq)} bp")

# Convert GenBank to FASTA
SeqIO.convert("input.gb", "genbank", "output.fasta", "fasta")
```

### 2. Alignment Analysis (Bio.Align & Bio.AlignIO)

**Reference:** `references/alignment.md`

Use for:
- Pairwise sequence alignment (global and local)
- Reading and writing multiple sequence alignments
- Using substitution matrices (BLOSUM, PAM)
- Calculating alignment statistics
- Customizing alignment parameters

**Quick example:**
```python
from Bio import Align

# Pairwise alignment
aligner = Align.PairwiseAligner()
aligner.mode = 'global'
alignments = aligner.align("ACCGGT", "ACGGT")
print(alignments[0])
```

### 3. Database Access (Bio.Entrez)

**Reference:** `references/databases.md`

Use for:
- Searching NCBI databases (PubMed, GenBank, Protein, Gene, etc.)
- Downloading sequences and records
- Fetching publication information
- Finding related records across databases
- Batch downloading with proper rate limiting

**Quick example:**

From bioassembly/antigravity-sage, MIT.

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