pypyr 0.3.2

pipeline runner command line to run pipelines defined in yaml

pypyr

pronounce how you like, but I generally say piper as in “piping down the valleys wild”

pypyr is a command line interface to run pipelines defined in yaml. Think of pypyr as a simple task runner that lets you run sequential steps.

Contents

• 1 Installation

  • 1.1 pip

  • 1.2 Python version

• 2 Usage

  • 2.1 Run your first pipeline

  • 2.2 Run a pipeline

  • 2.3 Get cli help

  • 2.4 Examples

• 3 Anatomy of a pypyr pipeline

  • 3.1 Pipeline yaml structure

  • 3.2 Built-in pipelines

  • 3.3 context_parser

    • 3.3.1 Built-in context parsers

    • 3.3.2 Roll your own context_parser

  • 3.4 steps

    • 3.4.1 Built-in steps

      • 3.4.1.1 pypyr.steps.contextset

      • 3.4.1.2 pypyr.steps.echo

      • 3.4.1.3 pypyr.steps.env

        • 3.4.1.3.1 envGet

        • 3.4.1.3.2 envSet

        • 3.4.1.3.3 envUnset

      • 3.4.1.4 pypyr.steps.py

      • 3.4.1.5 pypyr.steps.pypyrversion

      • 3.4.1.6 pypyr.steps.safeshell

      • 3.4.1.7 pypyr.steps.shell

    • 3.4.2 Roll your own step

  • 3.5 on_success

  • 3.6 on_failure

• 4 Testing (for pypyr-cli developers)

  • 4.1 Testing without worrying about dependencies

  • 4.2 If tox takes too long

  • 4.3 Day-to-day testing

• 5 Contribute

  • 5.1 Bugs

  • 5.2 Contribute to the core cli

  • 5.3 Plug-Ins

1 Installation

1.1 pip

$ pip install --upgrade pypyr

1.2 Python version

Tested against Python 3.6

2 Usage

2.1 Run your first pipeline

Run one of the built-in pipelines to get a feel for it:

$ pypyr --name echo --context "echoMe=Ceci n'est pas une pipe" --log 20

You can achieve the same thing by running a pipeline where the context is set in the pipeline yaml rather than as a –context argument:

$ pypyr --name magritte --log 20

Check here pypyr.steps.echo to see yaml that does this.

2.2 Run a pipeline

pypyr assumes a pipelines directory in your current working directory.

# run pipelines/mypipelinename.yaml with DEBUG logging level
$ pypyr --name mypipelinename

# run pipelines/mypipelinename.yaml with INFO logging level
$ pypyr --name mypipelinename --log 20

# run pipelines/mypipelinename.yaml with an input context. For this input to
# be available to your pipeline you need to specify a context_parser in your
# pipeline yaml.
$ pypyr --name mypipelinename --context 'mykey=value'

2.3 Get cli help

pypyr has a couple of arguments and switches you might find useful. See them all here:

$ pypyr -h

2.4 Examples

If you prefer reading code to reading words, https://github.com/pypyr/pypyr-example

3 Anatomy of a pypyr pipeline

3.1 Pipeline yaml structure

A pipeline is a .yaml file. Save pipelines to a pipelines directory in your working directory.

# This is an example showing the anatomy of a pypyr pipeline
# A pipeline should be saved as {working dir}/pipelines/mypipelinename.yaml.
# Run the pipeline from {working dir} like this: pypyr --name mypipelinename

# optional
context_parser: my.custom.parser

# mandatory.
steps:
  - my.package.my.module # simple step pointing at a python module in a package
  - mymodule # simple step pointing at a python file
  - name: my.package.another.module # complex step. It contains a description and in parameters.
    description: Optional description is for humans. It's any text that makes your life easier.
    in: #optional. In parameters are added to the context so that this step and subsequent steps can use these key-value pairs.
      parameter1: value1
      parameter2: value2

# optional.
on_success:
  - my.first.success.step
  - my.second.success.step

# optional.
on_failure:
  - my.failure.handler.step
  - my.failure.handler.notifier

3.2 Built-in pipelines

pipeline	description	how to run
donothing	Does what it says. Nothing.	pypyr –name donothing
echo	Echos context value echoMe to output.	pypyr –name echo –context “echoMe=text goes here” –log 20
pypyrversion	Prints the python cli version number.	pypyr –name pypyrversion –log 20
magritte	Thoughts about pipes.	pypyr –name magritte –log 20

3.3 context_parser

Optional.

A context_parser parses the pypyr –context input argument. The chances are pretty good that it will take the –context argument and put in into the pypyr context.

The pypyr context is a dictionary that is in scope for the duration of the entire pipeline. The context_parser can initialize the context. Any step in the pipeline can add, edit or remove items from the context dictionary.

3.3.1 Built-in context parsers

context parser	description	example input
pypyr.parser.commas	Takes a comma delimited string and returns a dictionary where each element becomes the key, with value to true. Don’t have spaces between commas unless you really mean it. "k1=v1, k2=v2" will result in a context key name of ' k2' not 'k2'.	pypyr –name pipelinename –context “param1,param2,param3” This will create a context dictionary like this: {‘param1’: True, ‘param2’: True, ‘param3’: True}
pypyr.parser.json	Takes a json string and returns a dictionary.	pypyr –name pipelinename –context '{“key1”:”value1”,”key2”:”value2”}'
pypyr.parser.jsonfile	Opens json file and returns a dictionary.	pypyr –name pipelinename –context './path/sample.json’
pypyr.parser.keyvaluepairs	Takes a comma delimited key=value pair string and returns a dictionary where each pair becomes a dictionary element. Don’t have spaces between commas unless you really mean it. "k1=v1, k2=v2" will result in a context key name of ' k2' not 'k2'.	pypyr –name pipelinename –context “param1=value1,param2=value2,param3=value3”
pypyr.parser.yamlfile	Opens a yaml file and writes the contents into the pypyr context dictionary. The top (or root) level yaml should describe a map, not a sequence. Sequence (this won’t work): - thing1 - thing2 Instead, do a map (aka dictionary): thing1: thing1value thing2: thing2value	pypyr –name pipelinename –context './path/sample.yaml’

3.3.2 Roll your own context_parser

import logging


# getLogger will grab the parent logger context, so your loglevel and
# formatting will inherit correctly automatically from the pypyr core.
logger = logging.getLogger(__name__)


def get_parsed_context(context_arg):
    """This is the signature for a context parser. Input context is the string received from pypyr --context 'value here'"""
    assert context_arg, ("pipeline must be invoked with --context set.")
    logger.debug("starting")

    # your clever code here. Chances are pretty good you'll be doing things with the input context string to create a dictionary.

    # function signature returns a dictionary
    return {'key1': 'value1', 'key2':'value2'}

3.4 steps

Mandatory.

steps is a list of steps to execute in sequence. A step is simply a bit of python that does stuff.

You can specify a step in the pipeline yaml in two ways:

• Simple step

  • a simple step is just the name of the python module.

  • pypyr will look in your working directory for these modules or packages.

  • For a package, be sure to specify the full namespace (i.e not just mymodule, but mypackage.mymodule).

    steps:
      - my.package.my.module # points at a python module in a package.
      - mymodule # simple step pointing at a python file

• Complex step

  • a complex step allows you to specify a few more details for your step, but at heart it’s the same thing as a simple step - it points at some python.

    steps:
      - name: my.package.another.module
        description: Optional Description is for humans. It's any yaml-escaped text that makes your life easier.
        in: #optional. In parameters are added to the context so that this step and subsequent steps can use these key-value pairs.
          parameter1: value1
          parameter2: value2

• You can freely mix and match simple and complex steps in the same pipeline.

• Frankly, the only reason simple steps are there is because I’m lazy and I dislike redundant typing.

3.4.1 Built-in steps

step	description	input context properties
pypyr.steps.contextset	Sets context values from already existing context values.	contextSet (dictionary)
pypyr.steps.echo	Echo the context value echoMe to the output.	echoMe (string)
pypyr.steps.env	Get, set or unset $ENVs.	envGet (dictionary) envSet (dictionary) envUnset (list)
pypyr.steps.py	Executes the context value pycode as python code.	pycode (string)
pypyr.steps.pypyrversion	Writes installed pypyr version to output.
pypyr.steps.safeshell	Runs the program and args specified in the context value cmd as a subprocess.	cmd (string)
pypyr.steps.shell	Runs the context value cmd in the default shell. Use for pipes, wildcards, $ENVs, ~	cmd (string)

3.4.1.1 pypyr.steps.contextset

Sets context values from already existing context values.

This is handy if you need to prepare certain keys in context where a next step might need a specific key. If you already have the value in context, you can create a new key (or update existing key) with that value.

So let’s say you already have context[‘currentKey’] = ‘eggs’. If you run newKey: currentKey, you’ll end up with context[‘newKey’] == ‘eggs’

For example, say your context looks like this,

key1: value1
key2: value2
key3: value3

and your pipeline yaml looks like this:

steps:
  - name: pypyr.steps.contextset
    in:
      contextSet:
        key2: key1
        key4: key3

This will result in context like this:

key1: value1
key2: value1
key3: value3
key4: value3

3.4.1.2 pypyr.steps.echo

Echo the context value echoMe to the output.

For example, if you had pipelines/mypipeline.yaml like this:

context_parser: pypyr.parser.keyvaluepairs
steps:
  - name: pypyr.steps.echo

You can run:

pypyr --name mypipeline --context "echoMe=Ceci n'est pas une pipe"

Alternatively, if you had pipelines/look-ma-no-params.yaml like this:

steps:
  - name: pypyr.steps.echo
    description: Output echoMe
    in:
      echoMe: Ceci n'est pas une pipe

You can run:

$ pypyr --name look-ma-no-params --log 20

3.4.1.3 pypyr.steps.env

Get, set or unset environment variables.

At least one of these context keys must exist:

• envGet

• envSet

• envUnset

This step will run whatever combination of Get, Set and Unset you specify. Regardless of combination, execution order is Get, Set, Unset.

See a worked example for environment variables here.

3.4.1.3.1 envGet

Get $ENVs into the pypyr context.

context['envGet'] must exist. It’s a dictionary.

Values are the names of the $ENVs to write to the pypyr context.

Keys are the pypyr context item to which to write the $ENV values.

For example, say input context is:

key1: value1
key2: value2
pypyrCurrentDir: value3
envGet:
  pypyrUser: USER
  pypyrCurrentDir: PWD

This will result in context:

key1: value1
key2: value2
key3: value3
pypyrCurrentDir: <<value of $PWD here, not value3>>
pypyrUser: <<value of $USER here>>

3.4.1.3.2 envSet

Set $ENVs from the pypyr context.

context['envSet'] must exist. It’s a dictionary.

Values are the keys of the pypyr context values to write to $ENV. Keys are the names of the $ENV values to which to write.

For example, say input context is:

key1: value1
key2: value2
key3: value3
envSet:
    MYVAR1: key1
    MYVAR2: key3

This will result in the following $ENVs:

$MYVAR1 = value1
$MYVAR2 = value3

Note that the $ENVs are not persisted system-wide, they only exist for the pypyr sub-processes, and as such for the subsequent steps during this pypyr pipeline execution. If you set an $ENV here, don’t expect to see it in your system environment variables after the pipeline finishes running.

3.4.1.3.3 envUnset

Unset $ENVs.

Context is a dictionary or dictionary-like. context is mandatory.

context['envUnset'] must exist. It’s a list. List items are the names of the $ENV values to unset.

For example, say input context is:

key1: value1
key2: value2
key3: value3
envUnset:
    MYVAR1
    MYVAR2

This will result in the following $ENVs being unset:

$MYVAR1
$MYVAR2

3.4.1.4 pypyr.steps.py

Executes the context value pycode as python code.

Will exec context['pycode'] as a dynamically interpreted python code block.

You can access and change the context dictionary in a py step. See a worked example here.

For example, this will invoke python print and print 2:

steps:
  - name: pypyr.steps.py
    description: Example of an arb python command. Will print 2.
    in:
      pycode: print(1+1)

3.4.1.5 pypyr.steps.pypyrversion

Outputs the same as:

pypyr --version

This is an actual pipeline, though, so unlike –version, it’ll use the standard pypyr logging format.

Example pipeline yaml:

steps:
  - pypyr.steps.pypyrversion

3.4.1.6 pypyr.steps.safeshell

Runs the context value cmd as a sub-process.

In safeshell, you cannot use things like exit, return, shell pipes, filename wildcards, environment variable expansion, and expansion of ~ to a user’s home directory. Use pypyr.steps.shell for this instead. Safeshell runs a program, it does not invoke the shell.

You can use context variable substitutions with curly braces. See a worked example for substitions here.

Escape literal curly braces with doubles: {{ for {, }} for }

Example pipeline yaml:

steps:
  - name: pypyr.steps.safeshell
    in:
      cmd: ls -a

See a worked example for shell power here.

3.4.1.7 pypyr.steps.shell

Runs the context value cmd in the default shell. On a sensible O/S, this is /bin/sh

Do all the things you can’t do with safeshell.

Friendly reminder of the difference between separating your commands with ; or &&:

• ; will continue to the next statement even if the previous command errored. It won’t exit with an error code if it wasn’t the last statement.

• && stops and exits reporting error on first error.

You can use context variable substitutions with curly braces. See a worked example for substitions here.

Escape literal curly braces with doubles: {{ for {, }} for }

Example pipeline yaml using a pipe:

steps:
  - name: pypyr.steps.shell
    in:
      cmd: ls | grep pipe; echo if you had something pipey it should show up;

See a worked example for shell power here.

3.4.2 Roll your own step

import logging


# getLogger will grab the parent logger context, so your loglevel and
# formatting will inherit correctly automatically from the pypyr core.
logger = logging.getLogger(__name__)


def run_step(context):
    """Run code in here. This shows you how to code a custom pipeline step.

    :param context: dictionary-like type
    """
    logger.debug("started")
    # you probably want to do some asserts here to check that the input context
    # dictionary contains the keys and values you need for your code to work.
    assert 'mykeyvalue' in context, ("context['mykeyvalue'] must exist for my clever step.")

    # it's good form only to use .info and higher log levels when you must.
    # For .debug() being verbose is very much encouraged.
    logger.info("Your clever code goes here. . . ")

    # Add or edit context items. These are available to any pipeline steps
    # following this one.
    context['existingkey'] = 'new value overwrites old value'
    context['mynewcleverkey'] = 'new value'

    logger.debug("done")

3.5 on_success

on_success is a list of steps to execute in sequence. Runs when steps: completes successfully.

You can use built-in steps or code your own steps exactly like you would for steps - it uses the same function signature.

3.6 on_failure

on_failure is a list of steps to execute in sequence. Runs when any of the above hits an unhandled exception.

If on_failure encounters another exception while processing an exception, then both that exception and the original cause exception will be logged.

You can use built-in steps or code your own steps exactly like you would for steps - it uses the same function signature.

4 Testing (for pypyr-cli developers)

4.1 Testing without worrying about dependencies

Run tox to test the packaging cycle inside a virtual env, plus run all tests:

# just run tests
$ tox -e dev -- tests
# run tests, validate README.rst, run flake8 linter
$ tox -e stage -- tests

4.2 If tox takes too long

The test framework is pytest. If you only want to run tests:

$ pip install -e .[dev,test]

4.3 Day-to-day testing

• Tests live under /tests (surprising, eh?). Mirror the directory structure of the code being tested.

• Prefix a test definition with test_ - so a unit test looks like

  def test_this_should_totally_work():

• To execute tests, from root directory:

  pytest tests

• For a bit more info on running tests:

  pytest --verbose [path]

• To execute a specific test module:

  pytest tests/unit/arb_test_file.py

5 Contribute

5.1 Bugs

Well, you know. No one’s perfect. Feel free to create an issue.

5.2 Contribute to the core cli

The usual jazz - create an issue, fork, code, test, PR. It might be an idea to discuss your idea via the Issues list first before you go off and write a huge amount of code - you never know, something might already be in the works, or maybe it’s not quite right for the core-cli (you’re still welcome to fork and go wild regardless, of course, it just mightn’t get merged back in here).

5.3 Plug-Ins

You’ve probably noticed by now that pypyr is built to be pretty extensible. You’ve probably also noticed that the core pypyr cli is deliberately kept light. The core cli is philosophically only a way of running a sequence of steps. Dependencies to external libraries should generally get their own package, so end-users can selectively install what they need rather than have a monolithic batteries-included application.

If you’ve got some custom context_parser or steps code that are useful, create a repo and bask in the glow of sharing with the open source community. Honor the pypyr Apache license please.

I generally name plug-ins pypyr-myplugin, where myplugin is likely some sort of dependency that you don’t want in the pypyr core cli. For example, pypyr-aws contains pypyr-steps for the AWS boto3 library. This is kept separate so that you don’t have to deal with yet another dependency you don’t need if your current project isn’t using AWS.

If you want your plug-in listed here for official cred, please get in touch via the Issues list. Get in touch anyway, would love to hear from you at https://www.345.systems/contact.