Package: varnaapi
VARNA API is a Python interface forVARNA(v3-93), a Java lightweight component and applet for drawing the RNA secondary structure.
VARNA allows users to produce drawing in a non-iteractive way via command line.
However, the command line might be massive and complicate in some use cases.
VARNA API aims to simplify such process.
Theonline documentationis available.!!! danger "Starting from v1.1.0, VARNA API uses1-indexedto count RNA bases. The change aims to better align with VARNA and ViennaRNA."ExampleThe command below highlights region 11-21 and adds a non-canonical base pair at position (14,20)
on secondary structure((((((.((((((........)))))).((((((.......))))))..)))))).java-cpVARNAv3-93.jarfr.orsay.lri.varna.applications.VARNAcmd-sequenceDBN"                                                       "-structureDBN"((((((.((((((........)))))).((((((.......))))))..))))))"-oexample.png-auxBPs"(14,20):color=#ff00ff"-highlightRegion"11-21"The equivalence using VARNA API would befromvarnaapiimportStructurev=Structure(structure="((((((.((((((........)))))).((((((.......))))))..))))))")v.add_highlight_region(11,21)v.add_aux_BP(14,20,edge5="s",color="#FF00FF")v.savefig("example.png")Installationpython3 -m pip install varnaapiUsageHere, we show the basic usage of varnaapi.
The first thing after importingvarnaapiis to setup the location of VARNA to use.!!! note "By default, the library assumes the VARNA v3-93 in the current folder is used (./VARNAv3-93.jar)"importvarnaapivarnaapi.set_VARNA(path_to_VARNA)Each drawing in VARNA is an object of class inherited from [BasicDraw][varnaapi.BasicDraw]. The standard class to draw from given secondary structure or/and RNA sequence is [Structure][varnaapi.Structure].ss="((((((.((((((........)))))).((((((.......))))))..))))))"v=varnaapi.Structure(structure=ss)One can call the member function#!python BasicDraw.savefig()with given file name to save the drawing. The format is eitherpngorsvg, that VARNA will determine from the file name.v.savefig("my_drawing.png")While using jupyter notebook, one can also set the optionshowto#!python Trueto show the drawing in the notebookv.savefig("my_drawing.png",show=True)or simply use the member function#!python BasicDraw.show().v.show()The later one creates a temporary file inpngformat for drawing.ConfigurationIn VARNA, one can chose the structure drawing algorithm, change the style for base pair, or hide backbone in drawing etc.
The full list of parameters with default value can be foundhere.
In library, the easiest way to modify these parameters is through the member function#!python BasicDraw.update().
Some parameters, such as algorithm, can be set up via specific function. The rest will be supported in future update.v.update(algorithm='naview',bpStyle='none',drawBackbone=False,bp='#006400')!!! note "Color parameters"
Value for all color parameters in VARNA API should be readable by the objectcolour.Color, such as human color name, hex, RGB etc.Save configurationThe library offers function to save the parameters setting in YAML format for the further use.v.dump_param('config.yml')Load configurationThere are two ways to load the saved configuration.
The first one is using the member function ofBasicDraw.v.load_param('config.yml')The second way is loading the configuration as a global setting in the opened session.varnaapi.load_config('config.yml')!!! note "Parameter value priority order"
VARNA API uses parameter values in the following order,i.e.if the value in the current order is undefined, then the next one is used- Value set by `varnaapi.BasicDraw.update()` or similar functions 
- Object Value loaded using `varnaapi.BasicDraw.load_param()`
- Global values loaded using `varnaapi.load_cofig()`
- Default parameter values.OperationsVARNA allows different operations on drawing, such as highlighting a region, adding auxiliary base pairs.
This can be achieved by using the proper functions. We invite users to read API for more details.v.add_highlight_region(1,6,radius=20)v.add_aux_bp(1,10,color='red')CreditsPlease kindly cite VARNAsupporting manuscriptif you use VARNA API in your research.
Downloadbibtexformat.Darty, K., Denise, A., & Ponty, Y. (2009). VARNA: Interactive drawing and editing of the RNA secondary structure. Bioinformatics, 25(15), 1974.