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Hello World! example for looper

This tutorial demonstrates how to install looper and use it to run a pipeline on a PEP project.

1. Install the latest version of looper:

pip install --user --upgrade looper

2. Download and unzip the hello_looper repository

The hello looper repository contains a basic functional example project (in /project) and a looper-compatible pipeline (in /pipeline) that can run on that project. Let's download and unzip it:

!wget https://github.com/pepkit/hello_looper/archive/refs/heads/master.zip
--2023-11-08 17:27:01--  https://github.com/pepkit/hello_looper/archive/refs/heads/master.zip
Resolving github.com (github.com)... 140.82.114.3
Connecting to github.com (github.com)|140.82.114.3|:443... connected.
HTTP request sent, awaiting response... 302 Found
Location: https://codeload.github.com/pepkit/hello_looper/zip/refs/heads/master [following]
--2023-11-08 17:27:01--  https://codeload.github.com/pepkit/hello_looper/zip/refs/heads/master
Resolving codeload.github.com (codeload.github.com)... 140.82.113.10
Connecting to codeload.github.com (codeload.github.com)|140.82.113.10|:443... connected.
HTTP request sent, awaiting response... 200 OK
Length: unspecified [application/zip]
Saving to: ‘master.zip’

master.zip              [ <=>                ]  13.37K  --.-KB/s    in 0.03s

2023-11-08 17:27:01 (472 KB/s) - ‘master.zip’ saved [13693]
!unzip master.zip
Archive:  master.zip
73ef08e38d3e17fd3d4f940282c80e3ee4dbb91f
   creating: hello_looper-master/
  inflating: hello_looper-master/.gitignore  
  inflating: hello_looper-master/.looper.yaml  
  inflating: hello_looper-master/.looper_pephub.yaml  
  inflating: hello_looper-master/.looper_pipestat.yaml  
  inflating: hello_looper-master/.looper_pipestat_shell.yaml  
  inflating: hello_looper-master/README.md  
   creating: hello_looper-master/data/
  inflating: hello_looper-master/data/frog1_data.txt  
  inflating: hello_looper-master/data/frog2_data.txt  
  inflating: hello_looper-master/looper_pipelines.md  
   creating: hello_looper-master/old_specification/
  inflating: hello_looper-master/old_specification/README.md  
   creating: hello_looper-master/old_specification/data/
  inflating: hello_looper-master/old_specification/data/frog1_data.txt  
  inflating: hello_looper-master/old_specification/data/frog2_data.txt  
   creating: hello_looper-master/old_specification/pipeline/
  inflating: hello_looper-master/old_specification/pipeline/count_lines.sh  
  inflating: hello_looper-master/old_specification/pipeline/pipeline_interface.yaml  
   creating: hello_looper-master/old_specification/project/
  inflating: hello_looper-master/old_specification/project/project_config.yaml  
  inflating: hello_looper-master/old_specification/project/sample_annotation.csv  
   creating: hello_looper-master/pipeline/
  inflating: hello_looper-master/pipeline/count_lines.sh  
  inflating: hello_looper-master/pipeline/pipeline_interface.yaml  
  inflating: hello_looper-master/pipeline/pipeline_interface_project.yaml  
   creating: hello_looper-master/pipeline_pipestat/
  inflating: hello_looper-master/pipeline_pipestat/count_lines.py  
  inflating: hello_looper-master/pipeline_pipestat/count_lines_pipestat.sh  
  inflating: hello_looper-master/pipeline_pipestat/pipeline_interface.yaml  
  inflating: hello_looper-master/pipeline_pipestat/pipeline_interface_shell.yaml  
  inflating: hello_looper-master/pipeline_pipestat/pipestat_output_schema.yaml  
   creating: hello_looper-master/project/
  inflating: hello_looper-master/project/project_config.yaml  
  inflating: hello_looper-master/project/sample_annotation.csv

3. Run it

Run it by changing to the directory and then invoking looper run on the project configuration file.

!looper run --looper-config hello_looper-master/.looper.yaml
Looper version: 1.5.2-dev
Command: run
Using default divvy config. You may specify in env var: ['DIVCFG']
Pipestat compatible: False
## [1 of 2] sample: frog_1; pipeline: count_lines
/home/drc/GITHUB/looper/master/looper/docs_jupyter/hello_looper-master/pipeline/count_lines.sh data/frog1_data.txt
Writing script to /home/drc/GITHUB/looper/master/looper/docs_jupyter/hello_looper-master/results/submission/count_lines_frog_1.sub
Job script (n=1; 0.00Gb): /home/drc/GITHUB/looper/master/looper/docs_jupyter/hello_looper-master/results/submission/count_lines_frog_1.sub
Compute node: databio
Start time: 2023-11-08 17:29:45
wc: data/frog1_data.txt: No such file or directory
Number of lines: 
## [2 of 2] sample: frog_2; pipeline: count_lines
/home/drc/GITHUB/looper/master/looper/docs_jupyter/hello_looper-master/pipeline/count_lines.sh data/frog2_data.txt
Writing script to /home/drc/GITHUB/looper/master/looper/docs_jupyter/hello_looper-master/results/submission/count_lines_frog_2.sub
Job script (n=1; 0.00Gb): /home/drc/GITHUB/looper/master/looper/docs_jupyter/hello_looper-master/results/submission/count_lines_frog_2.sub
Compute node: databio
Start time: 2023-11-08 17:29:45
wc: data/frog2_data.txt: No such file or directory
Number of lines:

Looper finished
Samples valid for job generation: 2 of 2
Commands submitted: 2 of 2
Jobs submitted: 2
{'Pipestat compatible': False, 'Commands submitted': '2 of 2', 'Jobs submitted': 2}


Voila! You've run your very first pipeline across multiple samples using looper!

Exploring the results

Now, let's inspect the hello_looper repository you downloaded. It has 3 components, each in a subfolder:

!tree hello_looper-master/*/
hello_looper-master/data/
├── frog1_data.txt
└── frog2_data.txt
hello_looper-master/pipeline/
├── count_lines.sh
└── pipeline_interface.yaml
hello_looper-master/project/
├── project_config.yaml
└── sample_annotation.csv

0 directories, 6 files

These are:

  • /data -- contains 2 data files for 2 samples. These input files were each passed to the pipeline.
  • /pipeline -- contains the script we want to run on each sample in our project. Our pipeline is a very simple shell script named count_lines.sh, which (duh!) counts the number of lines in an input file.
  • /project -- contains 2 files that describe metadata for the project (project_config.yaml) and the samples (sample_annotation.csv). This particular project describes just two samples listed in the annotation file. These files together make up a PEP-formatted project, and can therefore be read by any PEP-compatible tool, including looper.

When we invoke looper from the command line we told it to run project/project_config.yaml. looper reads the project/project_config.yaml file, which points to a few things:

The 3 folders (data, project, and pipeline) are modular; there is no need for these to live in any predetermined folder structure. For this example, the data and pipeline are included locally, but in practice, they are usually in a separate folder; you can point to anything (so data, pipelines, and projects may reside in distinct spaces on disk). You may also include more than one pipeline interface in your project_config.yaml, so in a looper project, many-to-many relationships are possible.

Looper config

The looper config contains paths to the project config, the output_dir as well as any dfine pipeline interfaces.

!cat hello_looper-master/.looper.yaml
pep_config: project/project_config.yaml # local path to pep config
# pep_config: pepkit/hello_looper:default  # you can also use a pephub registry path
output_dir: "results"
pipeline_interfaces:
  sample: pipeline/pipeline_interface.yaml

Project Config

The project config file contains the PEP version and sample annotation sheet. (see defining a project).

!cat hello_looper-master/project/project_config.yaml
pep_version: 2.0.0
sample_table: sample_annotation.csv

Pipeline Interface

The pipeline interface shows the pipeline_name, pipeline_type, as well as the var_templates and command_templates used for this pipeline.

!cat hello_looper-master/pipeline/pipeline_interface.yaml
pipeline_name: count_lines
pipeline_type: sample
var_templates:
  pipeline: '{looper.piface_dir}/count_lines.sh'
command_template: >
  {pipeline.var_templates.pipeline} {sample.file}

Alright, next let's explore what this pipeline stuck into our output_dir:

!tree $HOME/hello_looper_results
/home/nsheff/hello_looper_results
├── results_pipeline
└── submission
    ├── count_lines.sh_frog_1.log
    ├── count_lines.sh_frog_1.sub
    ├── count_lines.sh_frog_2.log
    ├── count_lines.sh_frog_2.sub
    ├── frog_1.yaml
    └── frog_2.yaml

2 directories, 6 files

Inside of an output_dir there will be two directories:

  • results_pipeline - a directory with output of the pipeline(s), for each sample/pipeline combination (often one per sample)
  • submissions - which holds a YAML representation of each sample and a log file for each submitted job

From here to running hundreds of samples of various sample types is virtually the same effort!

Running PEPs from PEPHub

Looper also supports running a PEP from PEPHub!

!cat hello_looper-master/.looper_pephub.yaml
pep_config: pepkit/hello_looper:default # pephub registry path or local path
output_dir: results
pipeline_interfaces:
  sample: pipeline/pipeline_interface.yaml
!looper run --looper-config hello_looper-master/.looper_pephub.yaml
Looper version: 1.5.2-dev
Command: run
Using default divvy config. You may specify in env var: ['DIVCFG']
No config key in Project, or reading project from dict
Processing project from dictionary...
Pipestat compatible: False
## [1 of 2] sample: frog_1; pipeline: count_lines
/home/drc/GITHUB/looper/master/looper/docs_jupyter/hello_looper-master/pipeline/count_lines.sh data/frog1_data.txt
Writing script to /home/drc/GITHUB/looper/master/looper/docs_jupyter/hello_looper-master/results/submission/count_lines_frog_1.sub
Job script (n=1; 0.00Gb): /home/drc/GITHUB/looper/master/looper/docs_jupyter/hello_looper-master/results/submission/count_lines_frog_1.sub
Compute node: databio
Start time: 2023-11-09 15:39:28
wc: data/frog1_data.txt: No such file or directory
Number of lines: 
## [2 of 2] sample: frog_2; pipeline: count_lines
/home/drc/GITHUB/looper/master/looper/docs_jupyter/hello_looper-master/pipeline/count_lines.sh data/frog2_data.txt
Writing script to /home/drc/GITHUB/looper/master/looper/docs_jupyter/hello_looper-master/results/submission/count_lines_frog_2.sub
Job script (n=1; 0.00Gb): /home/drc/GITHUB/looper/master/looper/docs_jupyter/hello_looper-master/results/submission/count_lines_frog_2.sub
Compute node: databio
Start time: 2023-11-09 15:39:28
wc: data/frog2_data.txt: No such file or directory
Number of lines:

Looper finished
Samples valid for job generation: 2 of 2
Commands submitted: 2 of 2
Jobs submitted: 2
{'Pipestat compatible': False, 'Commands submitted': '2 of 2', 'Jobs submitted': 2}


Pipestat compatible configurations

Looper can also be used in tandem with pipestat to report pipeline results.

!cat hello_looper-master/.looper_pipestat.yaml
pep_config: ./project/project_config.yaml # pephub registry path or local path
output_dir: ./results
pipeline_interfaces:
  sample:  ./pipeline_pipestat/pipeline_interface.yaml
pipestat:
  results_file_path: results.yaml

A few more basic looper options

Looper also provides a few other simple arguments that let you adjust what it does. You can find a complete reference of usage in the docs. Here are a few of the more common options:

For looper run:

  • -d: Dry run mode (creates submission scripts, but does not execute them)
  • --limit: Only run a few samples
  • --lumpn: Run several commands together as a single job. This is useful when you have a quick pipeline to run on many samples and want to group them.

There are also other commands:

  • looper check: checks on the status (running, failed, completed) of your jobs
  • looper summarize: produces an output file that summarizes your project results
  • looper destroy: completely erases all results so you can restart
  • looper rerun: rerun only jobs that have failed.

On your own

To use looper on your own, you will need to prepare 2 things: a project (metadata that define what you want to process), and pipelines (how to process data). To link your project to looper, you will need to define a project. You will want to either use pre-made looper-compatible pipelines or link your own custom-built pipelines. These docs will also show you how to connect your pipeline to your project.