This module provides an interface to the PAML (Phylogenetic Analysis by Maximum Likelihood) package of programs. Currently, interfaces to the programs codeml, baseml and yn00 as well as a Python re-implementation of chi2 have been included.
This module is available in Biopython 1.58 and later.
To use this module, you must have PAML version 4.1 or greater installed on your system.
The codeml interface is provided in the following module:
from Bio.Phylo.PAML import codeml
The interface is implemented as an object which maintains program
options. In order to run codeml, typically one provides a control file
which indicates the locations of an alignment file, a tree file and an
output file, along with a series of options dictating how the software
is to be run. In the
Codeml object, the three file locations are stored
as string attributes. The three file locations, as well as the location
of the desired working directory, may be specified in the
constructor as follows:
cml = codeml.Codeml( alignment="align.phylip", tree="species.tree", out_file="results.out", working_dir="./scratch", )
They may also be set individually:
cml = codeml.Codeml() cml.alignment = "align.phylip" cml.tree = "species.tree" cml.out_file = "results.out" cml.working_dir = "./scratch"
Note that all file locations are converted to locations relative to the working directory. PAML programs have a limit on the lengths of file location strings; converting to relative locations will shorten these strings, allowing you generally to sidestep this limitation.
The codeml runtime options are stored in a dictionary object that is keyed by the option names. For more information on the usage of these options, please refer to the PAML user manual.
The complete set of options and their current values may be printed:
>>> cml.print_options() verbose = None CodonFreq = None cleandata = None fix_blength = None NSsites = None fix_omega = None clock = None ncatG = None runmode = None fix_kappa = None fix_alpha = None Small_Diff = None method = None Malpha = None aaDist = None RateAncestor = None aaRatefile = None icode = None alpha = None seqtype = None omega = None getSE = None noisy = None Mgene = None kappa = None model = None ndata = None
Setting an option to a value of
None will cause it to be ignored by
codeml (it will be omitted from the final control file). Options may
be set by the
set_option() function and their values may be retrieved
>>> cml.set_options(clock=1) >>> cml.set_options(NSsites=[0, 1, 2]) >>> cml.set_options(aaRatefile="wag.dat") >>> cml.get_option("NSsites") [0, 1, 2]
NSsites option deserves special attention: in a codeml control
file, NSsites models are entered as a space-delimited list of numbers,
such as 0 1 2, whereas in the
Codeml object it is stored as a Python
Finally, options may be read in from an existing codeml control file
or they may be written to a new file. Writing to a file isn’t necessary,
as this is done automatically when executing the
run() method (see
below). The control file to read is provided as an argument to the
read_ctl_file() method, while the
write_ctl_file() method writes to
>>> cml.read_ctl_file("codeml.ctl") >>> cml.print_options() verbose = 1 CodonFreq = 2 cleandata = 1 fix_blength = None NSsites = 0 fix_omega = 0 clock = 0 ncatG = 8 runmode = 0 fix_kappa = 0 fix_alpha = 1 Small_Diff = 5e-07 method = 0 Malpha = 0 aaDist = 0 RateAncestor = 1 aaRatefile = dat/jones.dat icode = 0 alpha = 0.0 seqtype = 2 omega = 0.4 getSE = 0 noisy = 9 Mgene = 0 kappa = 2 model = 2 ndata = None >>> cml.ctl_file = "control2.ctl" >>> cml.write_ctl_file()
Executing the object’s
run() method will run codeml with the current
options and will return the parsed results in a dictionary object (see
below). You can also pass a number of optional arguments to the
verbose(boolean): codeml’s screen output is suppresed by default; set this argument to
Trueto see all of the output as it is generated. This is useful if codeml is failing and you need to see its error messages.
parse(boolean): set to
Falseto skip parsing the results.
run()will instead return
ctl_file(string): provide a path to an existing control file to execute. The file is not parsed and read into
Codeml’s options dictionary. If set to
None(default), the options dictionary is written to a control file, which is then used by codeml.
command(string): provide a path to the codeml executable. This is set to “codeml” by default, so if the program is in your system path, that should suffice. If it’s not in your system path or, for example, if you use multiple versions of PAML, you may instead provide the full path to the executable.
If the codeml process exits with an error, a
PamlError exception will
As previously stated, the
Codeml.run() method returns a dictionary
containing results parsed from codeml’s main output file.
Alternatively, an existing output file may be parsed using the
results = codeml.read()
The results dictionary is organized hierarchically and is (in most
cases) keyed in accordance with the terminology used in the output file.
Numeric values are automatically converted to numeric Python types. As
the output of codeml varies widely depending on the parameters used,
the contents of the results dictionary will vary accordingly. Similarly,
in the case of a runtime error, the results dictionary may be empty or
missing contents. Thus, it is advisable to use Python’s
method rather than
dict[key] in order to handle missing elements
All possible keys of the results dictionary are organized as follows:
Interfaces to baseml and yn00 are provided in the following modules:
from Bio.Phylo.PAML import baseml, yn00 bml = baseml.Baseml() yn = yn00.Yn00()
Yn00 share the same methods and attributes as
Codeml, and are
thus used in the same manner. It should be noted, however, that
does not have a tree attribute, as yn00 does not require a tree file.
The parameters available in the Baseml options are:
>>> bml.print_options() verbose = None cleandata = None fix_blength = None nparK = None model_options = None clock = None ncatG = None runmode = None fix_kappa = None fix_alpha = None noisy = None method = None fix_rho = None Malpha = None nhomo = None RateAncestor = None icode = None rho = None alpha = None getSE = None Small_Diff = None Mgene = None kappa = None model = None ndata = None
All of the possible contents of the
Baseml results file are:
The parameters available in the
Yn00 options are:
>>> yn.print_options() commonf3x4 = None weighting = None icode = None ndata = None verbose = None
All of the possible contents of the
Yn00 results file are:
chi2 module offers an easy method to retrieve p-values from a
Chi-squared cumulative distribution function for likelihood ratio tests,
which are performed frequently when using PAML programs. As of the
current version of PAML, the chi2 program does not allow passing both
a test statistic and the degrees of freedom as command-line arguments.
chi2 module currently consists of a re-implementation of
Ziheng Yang’s original code in pure Python. For most cases, this should
not affect you, however using very large numbers of degrees of freedom,
such as in the FMutSel vs FMutSel0 model test in codeml (41 degrees of
freedom), this Python version runs significantly slower than the
To retrieve a p-value, simply import the module
from Bio.Phylo.PAML.chi2 import cdf_chi2
And use the
>>> df = 2 >>> statistic = 7.21 >>> cdf_chi2(df, statistic) 0.027187444813595696