Truncating branch length values of Phylogenetic tree with biopython

Question

I have been using biopython 1.72 to display my phylogenetic tree files.

1. Using the function 'Phylo.draw(pars_tree, branch_labels=lambda c: c.branch_length)' to display branch lengths as well on tree, the tree displays the branch lengths as including all numbers after decimal. While I want the numbers to be truncated to two decimal places. Following is a python method that truncates upto "the number required" decimal places.

   def truncate(n, decimals=0): multiplier = 10 ** decimals return int(n * multiplier) / multiplier truncate (12.567, 2) #Using function 12.56 #Output Can I use such method with biopython for branch lengths?

2. 'Phylo.draw' function opens the window which is very narrow and if the tree file is larger, all the branches are overlapped and it gets difficult to read what is written. Does anyone know any better display method?

Following is the example code, I have been using:

from Bio import Phylo
from Bio.Phylo.TreeConstruction import *
from Bio import AlignIO

aln = AlignIO.read(open('example.phy'), 'phylip')

calculator = DistanceCalculator()
dm = calculator.get_distance(aln)

constructor = DistanceTreeConstructor()
njtree = constructor.nj(dm)
starting_tree = njtree
scorer = ParsimonyScorer()
searcher = NNITreeSearcher(scorer)
constructor = ParsimonyTreeConstructor(searcher, starting_tree)
pars_tree = constructor.build_tree(aln)
Phylo.draw(pars_tree, branch_labels=lambda c: c.branch_length)

I have an msa file as input and it gives a tree, which looks like:

                                                         _______ Human
                                                 _______|
                                                |       |_______ Chimpanzee
                                         _______|
                                        |       |        _______ Dog
                                 _______|       |_______|
                                |       |               |_______ Cow
                         _______|       |
                        |       |       |_______________________ Elephant
                 _______|       |
                |       |       |_______________________________ Mouse
                |       |
         _______|       |_______________________________________ Platypus
        |       |
        |       |        _______________________________________ Anole_lizard
        |       |_______|
  ______|               |        _______________________________ Chicken
 |      |               |_______|
 |      |                       |_______________________________ Zebra_finch
 |      |
 |      |_______________________________________________________ Xenopus
_|
 |       _______________________________________________________ Zebrafish
 |______|
 |      |_______________________________________________________ Fugu
 |
 |______________________________________________________________ Amphioxus

Answer 1

Apologies, try the following,

allclades = list(pars_tree.find_clades(order='level'))
for i, blength in enumerate(allclades):
        printf(blength=%.2f, blength)

"allclades" is a dictionary rather than a simple array.

If this fails I would examine the allclades data structure either using pprint (directly) or using printStruct via the following code,

>>> d = [{'a1':1, 'a2':2, 'a3':3}, [1,2,3], [{'b1':1, 'b2':2}, {'c1':1}], 'd1', 'd2', 'd3']
>>> printStruct(d)

def printStruct(struc, indent=0):
  if isinstance(struc, dict):
    print '  '*indent+'{'
    for key,val in struc.iteritems():
      if isinstance(val, (dict, list, tuple)):
        print '  '*(indent+1) + str(key) + '=> '
        printStruct(val, indent+2)
      else:
        print '  '*(indent+1) + str(key) + '=> ' + str(val)
    print '  '*indent+'}'
  elif isinstance(struc, list):
    print '  '*indent + '['
    for item in struc:
      printStruct(item, indent+1)
    print '  '*indent + ']'
  elif isinstance(struc, tuple):
    print '  '*indent + '('
    for item in struc:
      printStruct(item, indent+1)
    print '  '*indent + ')'
  else: print '  '*indent + str(struc)

Once you know the structure you unravel it accordingly to get to the branch lengths and then issue a printf command to round them to 2 dp.

Goodluck

Answer 2

The universal coding way to do this is the printf command regardless of language (sprintf is used language depending), for Python this is,

blength = 0.22342
printf("Taxa A, blength=%.2f", blength)

---

Output

Taxa A, 0.22

---

The following may be useful to your context:

import numpy
allclades = list(pars_tree.find_clades(order='level'))
for blength in enumerate(allclades):
        printf(blength=%.2f, blength)

Goodluck