Style Guide

Coding style

This style guide lays down coding conventions in the CGAT repository. For new scripts, follow the guidelines below.

As the repository has grown over years and several people contributed, the style between scripts can vary. For older scripts, follow the style within a script/module. If you want to apply the newer style, make consistent changes across the script.

In general, we want to adhere to the following conventions:

  • Variable names are lower case throughout with underscores to separate words, such as peaks_in_interval = 0

  • Function names start with a lower case character and a

    verb. Additional words start in upper case, such as doSomethingWithData()

  • Class names start with an upper case character, additional words

    start again in upper case, such as class AFancyClass():

  • Class methods follow the same convention as functions, such as


  • Class attributes follow the same convention as variables, such

    as self.factor

  • Global variables - in the rare cases they are used, are upper case

    throughout such as DEBUG=False

  • Module names should start with an uppercase letter, for example, in order to distinguish them from built-in and third-party python modules.

  • Script names are lower-case throughout with underscores to separate words, for example, or

  • Cython extensions to scripts (via pyximport) should be put into the script name starting with an underscore. For example, The extensions to are in _bam2geneprofile.pyx.

For new scripts, use the template

The general rule is to write easily readable and maintainable code. Thus, please

  • document code liberally and accurately

  • make use of whitespaces and line-breaks to break long statements

    into easily readable statements.

In case of uncertainty, follow the python style guides as much as possible. The relevant documents are:

For documenting CGAT code, we follow the conventions for documenting python code:

In terms of writing scripts, we follow the following conventions:

  • Each script should define the -h and --help options to give command line help usage.

  • For tabular output, scripts should output tsv formatted tables. In these tables, records are separated by new-line characters and fields by tab characters. Lines with comments are started by the # character and are ignored. The first uncommented line should contain the column headers. For example:

    # This is a comment
    gene_id length
    gene1   1000
    gene2   2000
    # Another comment
  • Scripts should follow the unix philosophy. They should concentrate on one task and do it well. Ideally, the major input and output can be read from and written to standard input and standard output, respectively.

  • The names of scripts should be meaningful. Most of our scripts perform data transformation of one kind of another, these are often called The distinctions can be subtle. Examples are:

    <no title>

    Input is gtf, output is gtf. This script manipulates gene sets (filtering, merging, ...).

    <no title>

    Input is gtf, output is gff. This script takes gene sets and changes the hierarchical description within a gtf file to the flat description of features in a gff file. For example, this script can define gene territories, regulatory domains or genomic annotations based on a gene set.

    <no title>

    Input is bed, output is gff. As both formats describe intervals in the genome, this script basically does a conversion between the two formats.

    Quite a few scripts contain the 2table or 2stats. These compute, respectively, properties or summary statistics for entries in a file. For example:

    <no title>

    Input is gtf. For each gene or transcript, compute selected properties. If there are 10,000 genes in the input, the output table will contain 10,000 rows.

    <no title>

    Input is gff. Compute summary statistics across all features in the file. Here, aggregate sizes or similar by feature type or name per chromosome. No matter if there are 10,000 or 100,000 interval is the input, the output will be have the same number of rows.

Where to put code

Different parts of the code base go into separate directories.

Scripts are python code that contains a main() function and are intended to be executed. Scripts go into the directory /scripts
Modules contain supporting code and are imported by scripts or other modules. Modules go into the directory /CGAT.
Pipeline scripts and modules go into the directory /CGATPipelines.


All components of a pipeline should go into the CGATPipelines directory. The basic layout of a pipeline is:

The main pipeline code. Pipelines start with the word pipeline and follow the conventions for script names, all lower case with underscores separating words.
Default values for pipeline configuration values.
Configuration script for sphinxreport.
Configuration script for sphinxreport.
Sphinxreport for pipeline.
Python utility methods and classes specific to this pipeline. Once methods and classes are shared between pipelines, consider moving them to a separate module.
R utility functions specific to this pipeline.
  • Make sure that the pipeline.ini file exists and contains example/default values with annotation.
  • Make sure that the pipeline can be imported from any directory, especially those not containing any data files or configuration files. This is important for the documentation of the pipeline to be built.

Other guidelines

  • Only add source code and required data to the repository. Do not add .pyc files, backup files created by your editor or other files.
  • In order to build documentation, each script, module and pipeline needs to be importable. Thus, make sure that when your pipeline depends on specific files, it does not fail when imported but not executed.


Writing doc-strings

Functions should be documented through their doc-string using restructured text. For example:

def computeValue( name, method, accuracy=2):

    :param name: The name to use.
    :type name: str.
    :param method: method to use.
    :type state: choice of ('empirical', 'parametric')
    :param accuracy:
    :type accuracy: integer
    :returns:  int -- the value
    :raises: AttributeError, KeyError

Writing documentation for scripts

Please follow the example in <no title> for documenting scripts. In addition, please pay attention to the following:

  • Declare input data types for genomic data sets in optparse using the metavar keyword. For example:

    parser.add_option( "--extra-intervals", dest = "extra_intervals",
                    metavar="bed", help = "..." )

    Setting the type permits the script to be integrated into workflow sytemns such as galaxy.

  • Please provide a meaningful example in the command line help.

  • Be verbose. Something that is not documented within a script will not be used.

  • Add meaningful tags to your scripts (:Tags:) so that they can be grouped into categories. Please choose from the following controlled vocabulary. If needed, additional terms can be added to this list.

    • Broad Themes

      • Genomics
      • NGS
      • MultipleAlignment
      • GenomeAlignment
      • Intervals
      • Genesets
      • Sequences
      • Variants
      • Protein
    • Formats

      • BAM
      • BED
      • GFF
      • GTF
      • FASTA
      • FASTQ
      • WIGGLE
      • PSL
      • CHAIN
    • Actions

      • Summary - summarizing entities within a file, such as counting the number of intervals within a file, etc.
      • Annotation - annotating individual entities within a file, such as adding length, composition, etc. to intervals.
      • Comparison - comparing the same type of entities, such as overlapping to sets of intervals.
      • Conversion - converting between different formats for the similar types of objects (Intervals in gff/bed format).
      • Transformation - transforming one entity into another, such as transforming intervals into sequences.
      • Manipulation - changing entities within a file, such as filtering sequences.

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