FastPhylo-py

Molecular sequence analysis for Python — fast pairwise distances and neighbour-joining trees for DNA, RNA, and protein sequences.

import fastphylo

aln  = fastphylo.read("sequences.fasta")          # FASTA, Stockholm, or Phylip
dm   = fastphylo.distance_matrix(aln)             # k2p for DNA, WAG for protein
tree = fastphylo.fnj(dm)
print(tree.to_newick())

Features

Reads FASTA, Stockholm, and Phylip files; format auto-detected from extension and content
DNA/RNA distances: Hamming, Jukes-Cantor, Kimura 2-parameter (default), Tamura-Nei 93 — computed by a fast C++ backend with SIMD (SSE2 / NEON)
Protein distances: maximum-likelihood estimation under WAG (default), LG, JTT, Dayhoff, BLOSUM62, VT, cpREV, MtREV, RtREV, HIVb, HIVw, DCMUT, JTT-DCMut, and PMB, using a Brent optimizer written in C++
Tree reconstruction: Neighbour-Joining, Fast NJ, and BioNJ (with branch lengths) via the FastPhylo library
Branch length estimation: fit_branch_lengths fits branch lengths to any tree topology by L1-minimisation against a distance matrix (requires scipy)
Distance matrix access: integer or taxon-name indexing, copy(), zeros() factory, NumPy and Phylip export
Multiple alignment: optional FAMSA integration for unaligned input
Pure-Python sequence types with Stockholm annotation support (organism, AC, description); edge-set Tree with to_newick() and merge()

Installation

pip install fastphylo

Optional extras:

pip install fastphylo[align]    # multiple-sequence alignment (pyfamsa)
pip install scipy               # branch length fitting (fit_branch_lengths)

Quick start

Aligned input → tree

import fastphylo

aln  = fastphylo.read("alignment.sto")            # Stockholm, FASTA, or Phylip
dm   = fastphylo.distance_matrix(aln, model="k2p")
tree = fastphylo.fnj(dm)
print(tree.to_newick())

Unaligned input → align → tree

import fastphylo

seqs = fastphylo.read("sequences.fasta")          # unaligned OK
aln  = fastphylo.align(seqs)                      # requires fastphylo[align]
dm   = fastphylo.distance_matrix(aln)
tree = fastphylo.fnj(dm)
print(tree.to_newick())

Protein sequences

import fastphylo

aln  = fastphylo.read("proteins.fasta")
dm   = fastphylo.distance_matrix(aln, model="LG")
tree = fastphylo.bionj(dm)                        # BioNJ with branch lengths
print(tree.to_newick())

Branch length fitting

NJ and FNJ return topology only (branch lengths are not computed). Use fit_branch_lengths to fit branch lengths to any tree topology by minimising the L1 deviation from the distance matrix:

import fastphylo

aln  = fastphylo.read("alignment.fasta")
dm   = fastphylo.distance_matrix(aln)
tree = fastphylo.fnj(dm)                          # fast topology, no lengths

tree = fastphylo.fit_branch_lengths(tree, dm)     # requires scipy
print(tree.to_newick())                           # now includes branch lengths

This solves a linear program: branch lengths are chosen to minimise sum |path_distance(i,j) − dm[i,j]| over all leaf pairs, subject to non-negative branch lengths.

Distance matrix access

dm = fastphylo.distance_matrix(aln)

# Integer or name-based indexing
d = dm[0, 1]
d = dm["human", "mouse"]

# Set elements
dm["human", "mouse"] = 0.15
dm["mouse", "human"] = 0.15

# Build a matrix manually
dm = fastphylo.DistanceMatrix.zeros(["human", "mouse", "rat"])
dm["human", "mouse"] = dm["mouse", "human"] = 0.15
dm["human", "rat"]   = dm["rat",   "human"] = 0.22
dm["mouse", "rat"]   = dm["rat",   "mouse"] = 0.08

# Copy, NumPy array, Phylip string
dm2  = dm.copy()
arr  = dm.to_numpy()
text = dm.to_phylip()

API overview

Function / class	Description
`fastphylo.read(path)`	Read FASTA / Stockholm / Phylip → `SequenceCollection` or `Alignment`
`fastphylo.align(seqs)`	Align with FAMSA → `Alignment`
`fastphylo.distance_matrix(aln, model=…)`	Compute pairwise distances → `DistanceMatrix`
`evolution.nj(dm)` / `fnj(dm)` / `bionj(dm)`	Tree reconstruction → `Tree`
`fastphylo.fit_branch_lengths(tree, dm)`	L1-optimal branch lengths for a given topology
`DistanceMatrix.zeros(names)`	Create an all-zero matrix with taxon names
`DistanceMatrix.copy()`	Deep copy
`DistanceMatrix.to_numpy()`	Export as NumPy array
`DistanceMatrix.to_phylip()`	Export as Phylip-format string
`Tree.to_newick()`	Newick string
`Tree.merge(other)`	Union of two edge-set trees

Distance models

Sequences	Model string	Notes
DNA / RNA	`"hamming"`	Raw mismatch count
DNA / RNA	`"jc"`	Jukes-Cantor
DNA / RNA	`"k2p"` (default)	Kimura 2-parameter
DNA / RNA	`"tn93"`	Tamura-Nei 93
Protein	`"WAG"` (default)	Whelan & Goldman
Protein	`"LG"`, `"JTT"`, `"Dayhoff"`, …	14 models total

RNA is handled transparently (U → T at the C++ boundary).

Requirements

Python ≥ 3.12
NumPy ≥ 1.24
A C compiler (for the bundled FastPhylo extension, built automatically by pip)

Optional:

pyfamsa ≥ 0.6.0 — multiple-sequence alignment (pip install fastphylo[align])
scipy — branch length fitting via fit_branch_lengths (pip install scipy)

License

GPLv3 — see FastPhylo for the upstream C++ library.

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Release history Release notifications | RSS feed

1.1.1

Aug 12, 2026

This release

1.1.0

Aug 12, 2026

1.0.0

Jul 29, 2026

0.2.1

Jul 24, 2026

0.1.0

May 19, 2026

fastphylo 1.1.0

FastPhylo-py

Features

Installation

Quick start

Aligned input → tree

Unaligned input → align → tree

Protein sequences

Branch length fitting

Distance matrix access

API overview

Distance models

Requirements

License

Key dates

1 maintainer

License

Requires

Provides Extra

Classifiers

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