pypyr

pipeline runner command line to run pipelines defined in yaml

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Project description

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 define and run sequential steps. Like a turbo-charged shell script, but less finicky.

You can run loops, conditionally execute steps based on conditions you specify, wait for status changes before continuing, break on failure conditions or swallow errors. Pretty useful for orchestrating continuous integration, continuous deployment and devops operations.

1 Installation

1.1 pip

$ pip install --upgrade pypyr

1.2 python version

Tested against Python >=3.6

1.3 docker

Stuck with an older version of python? Want to run pypyr in an environment that you don’t control, like a CI server somewhere?

You can use the official pypyr docker image as a drop-in replacement for the pypyr executable. https://hub.docker.com/r/pypyr/pypyr/

$ docker run pypyr/pypyr echo "Ceci n'est pas une pipe"

2 Usage

2.1 Run your first pipeline

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

$ pypyr echo "Ceci n'est pas une pipe"

You can achieve the same thing by running a pipeline where the context is set in the pipeline yaml rather than passed in as the 2nd positional argument:

$ pypyr magritte

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 mypipelinename --loglevel 10

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

# If you don't specify --loglevel it defaults to 20 - INFO logging level.
$ pypyr mypipelinename

# run pipelines/mypipelinename.yaml. The 2nd argument is any arbitrary string,
# known as the input context argument. For this input argument to be available
# to your pipeline you need to specify a context parser in your pipeline yaml.
$ pypyr mypipelinename arbitrary_string_here

# run pipelines/mypipelinename.yaml with an input context in key-value
# pair format. For this input to be available to your pipeline you need to
# specify a context_parser like pypyr.parser.keyvaluepairs in your
# pipeline yaml.
$ pypyr mypipelinename "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. pypyr uses YAML version 1.2.

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 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
    run: True # optional. Runs this step if True, skips step if False. Defaults to True if not specified.
    skip: False # optional. Skips this step if True, runs step if False. Defaults to False if not specified.
    swallow: False # optional. Swallows any errors raised by the step. Defaults to False if not specified.

# 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 donothing
echo	Echos context value echoMe to output.	pypyr echo "text goes here"
pypyrversion	Prints the python cli version number.	pypyr pypyrversion
magritte	Thoughts about pipes.	pypyr magritte

3.3 context_parser

Optional.

A context_parser parses the pypyr command’s context input argument. This is the second positional argument from the command line.

The chances are pretty good that the context_parser will take the context command 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 pipelinename "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 pipelinename '{"key1":"value1","key2":"value2"}'
pypyr.parser.jsonfile	Opens json file and returns a dictionary.	pypyr pipelinename "./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 pipelinename "param1=value1,param2=value2,param3=value3"
pypyr.parser.list	Takes a comma delimited string and returns a list in context with name argList. Don’t have spaces between commas unless you really mean it. "v1, v2" will result in argList[1] being ' v2' not 'v2'.	pypyr pipelinename "param1,param2,param3" This will create a context dictionary like this: {‘argList’: [‘param1’, ‘param2’, ‘param3’]}
pypyr.parser.string	Takes any arbitrary string and returns a string in context with name argString.	pypyr pipelinename "arbitrary string here" This will create a context dictionary like this: {‘argString’: ‘arbitrary string here’}
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 pipelinename "./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.

    Args:
      context_arg: string. Passed from command-line invocation where
                   pypyr pipelinename 'this is the context_arg'

    Returns:
      dict. This dict will initialize the context for the pipeline run.
    """
    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_arg 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 Step decorators

3.4.1.1 Decorators overview

Complex steps have various optional step decorators that change how or if a step is run.

Don’t bother specifying these unless you want to deviate from the default values.

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
    foreach: [] # optional. Repeat the step once for each item in this list.
    run: True # optional. Runs this step if True, skips step if False. Defaults to True if not specified.
    skip: False # optional. Skips this step if True, runs step if False. Defaults to False if not specified.
    swallow: False # optional. Swallows any errors raised by the step. Defaults to False if not specified.
    while: # optional. repeat step until stop is True or max iterations reached.
      stop: '{keyhere}' # loop until this evaluates True.
      max: 1 # max loop iterations to run. integer. Defaults None (infinite).
      sleep: 0 # sleep between iterations, in seconds. Decimals allowed. Defaults 0.
      errorOnMax: False # raise error if max reached. Defaults False.

decorator	type	description	default
foreach	list	Run the step once for each item in the list. The iterator is context['i']. The run, skip & swallow decorators evaluate dynamically on each iteration. So if during an iteration the step’s logic sets run=False, the step will not execute on the next iteration.	None
in	dict	Add this to the context so that this step and subsequent steps can use these key-value pairs. in evaluates once at the beginning of step execution, before the foreach and while decorators. It does not re-evaluate for each loop iteration.	None
run	bool	Runs this step if True, skips step if False.	True
skip	bool	Skips this step if True, runs step if False. Evaluates after the run decorator. If this looks like it’s merely the inverse of run, that’s because it is. Use whichever suits your pipeline better, or combine run and skip in the same pipeline to toggle at runtime which steps you want to execute.	False
swallow	bool	If True, ignore any errors raised by the step and continue to the next step. pypyr logs the error, so you’ll know what happened, but processing continues.	False
while	dict	Repeat step until stop is True, or until max iterations reached. You have to specify either max or stop. The loop position counter is context['whileCounter'] If you specify both max and stop, the loop exits when stop is True as long as it’s still under max iterations. max will exit the loop even if stop is still False. If you want to error and stop processing when max exhausts (maybe you are waiting for stop to reach True but want to timeout after max) set errorOnMax to True.	None

All step decorators support Substitutions.

If no looping decorators are specified, the step will execute once (depending on the conditional decorators’ settings).

If all of this sounds complicated, don’t panic! If you don’t bother with any of these the step will just run once by default.

3.4.1.2 decorator bool evaluation

Note that for all bool values, the standard Python truth value testing rules apply. https://docs.python.org/3/library/stdtypes.html#truth-value-testing

Simply put, this means that 1, TRUE, True and true will be True.

None/Empty, 0,’’, [], {} will be False.

3.4.1.3 Decorator order of precedence

Decorators can interplay, meaning that the sequence of evaluation is important.

run or skip controls whether a step should execute on any given loop iteration, without affecting continued loop iteration.
run could be True but skip True will still skip the step.
A step can run multiple times in a foreach loop for each iteration of a while loop.
swallow can evaluate dynamically inside a loop to decide whether to swallow an error or not on a particular iteration.

in # in evals once and only once at the beginning of step
  -> while # everything below loops inside while
    -> foreach # everything below loops inside foreach
      -> run # evals dynamically on each loop iteration
       -> skip # evals dynamically on each loop iteration after run
          [>>>actual step execution here<<<]
            -> swallow # evaluated dynamically on each loop iteration

3.4.1.4 Decorator examples

example	link
conditional step decorators	step decorators
foreach looping	foreach
foreach with dynamic conditional decorator evaluation.	foreach dynamic conditionals
while looping	while decorator
while with sleep intervals	while with sleep
while combined with foreach	while foreach
while with error on reaching max or never reaching a stop condition.	while exhaust
while loop that runs infinitely	while infinite

3.4.2 Built-in steps

step	description	input context properties
pypyr.steps.assert	Stop pipeline if item in context is not as expected.	assertThis (any) assertEquals (any)
pypyr.steps.contextclear	Remove specified items from context.	contextClear (list)
pypyr.steps.contextclearall	Wipe the entire context.
pypyr.steps.contextmerge	Merges values into context, preserving the existing context hierarchy.	contextMerge (dict)
pypyr.steps.contextset	Set context values from already existing context values.	contextSet (dict)
pypyr.steps.contextsetf	Set context keys from formatting expressions with {token} substitutions.	contextSetf (dict)
pypyr.steps.default	Set default values in context. Only set values if they do not exist already.	defaults (dict)
pypyr.steps.echo	Echo the context value echoMe to the output.	echoMe (string)
pypyr.steps.env	Get, set or unset $ENVs.	envGet (dict) envSet (dict) envUnset (list)
pypyr.steps.fetchjson	Loads json file into pypyr context.	fetchJsonPath (path-like)
pypyr.steps.fetchyaml	Loads yaml file into pypyr context.	fetchYamlPath (path-like)
pypyr.steps.fileformat	Parse file and substitute {tokens} from context.	fileFormatIn (path-like) fileFormatOut (path-like)
pypyr.steps.fileformatjson	Parse json file and substitute {tokens} from context.	fileFormatJsonIn (path-like) fileFormatJsonOut (path-like)
pypyr.steps.fileformatyaml	Parse yaml file and substitute {tokens} from context.	fileFormatYamlIn (path-like) fileFormatYamlOut (path-like)
pypyr.steps.filereplace	Parse input file and replace search strings.	fileReplaceIn (path-like) fileReplaceOut (path-like) fileReplacePairs (dict)
pypyr.steps.py	Executes the context value pycode as python code.	pycode (string)
pypyr.steps.pype	Run another pipeline from within the current pipeline.	pype (dict)
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)
pypyr.steps.tar	Archive and/or extract tars with or without compression. Supports gzip, bzip2, lzma.	tarExtract (dict) tarArchive (dict)

3.4.2.1 pypyr.steps.assert

Assert that something is True or equal to something else.

Uses these context keys:

assertThis
- mandatory
- If assertEquals not specified, evaluates as a boolean.
assertEquals
- optional
- If specified, compares assertThis to assertEquals

If assertThis evaluates to False raises error.

If assertEquals is specified, raises error if assertThis != assertEquals.

Supports Substitutions.

Examples:

# continue pipeline
assertThis: True
# stop pipeline
assertThis: False

or with substitutions:

interestingValue: True
assertThis: '{interestingValue}' # continue with pipeline

Non-0 numbers evalute to True:

assertThis: 1 # non-0 numbers assert to True. continue with pipeline

String equality:

assertThis: 'up the valleys wild'
assertEquals: 'down the valleys wild' # strings not equal. stop pipeline.

String equality with substitutions:

k1: 'down'
k2: 'down'
assertThis: '{k1} the valleys wild'
assertEquals: '{k2} the valleys wild' # substituted strings equal. continue pipeline.

Number equality:

assertThis: 123.45
assertEquals: 123.45 # numbers equal. continue with pipeline.

Number equality with substitutions:

numberOne: 123.45
numberTwo: 678.9
assertThis: '{numberOne}'
assertEquals: '{numberTwo}' # substituted numbers not equal. Stop pipeline.

Complex types:

complexOne:
  - thing1
  - k1: value1
    k2: value2
    k3:
      - sub list 1
      - sub list 2
complexTwo:
  - thing1
  - k1: value1
    k2: value2
    k3:
      - sub list 1
      - sub list 2
assertThis: '{complexOne}'
assertEquals: '{complexTwo}' # substituted types equal. Continue pipeline.

See a worked example for assert here.

3.4.2.2 pypyr.steps.contextclear

Remove the specified items from the context.

Will iterate contextClear and remove those keys from context.

For example, say input context is:

key1: value1
key2: value2
key3: value3
key4: value4
contextClear:
    - key2
    - key4
    - contextClear

This will result in return context:

key1: value1
key3: value3

Notice how contextClear also cleared itself in this example.

3.4.2.3 pypyr.steps.contextclearall

Wipe the entire context. No input context arguments required.

You can always use contextclearall as a simple step. Sample pipeline yaml:

steps:
  - my.arb.step
  - pypyr.steps.contextclearall
  - another.arb.step

3.4.2.4 pypyr.steps.contextmerge

Merges values into context, preserving the existing hierarchy while only updating the differing values as specified in the contextmerge input.

By comparison, contextset and contextsetf overwrite the destination hierarchy that is in context already,

This step merges the contents of the context key contextMerge into context. The contents of the contextMerge key must be a dictionary.

For example, say input context is:

key1: value1
key2: value2
key3:
    k31: value31
    k32: value32
contextMerge:
    key2: 'aaa_{key1}_zzz'
    key3:
        k33: value33_{key1}
    key4: 'bbb_{key2}_yyy'

This will result in return context:

key1: value1
key2: aaa_value1_zzz
key3:
    k31: value31
    k32: value32
    k33: value33_value1
key4: bbb_aaa_value1_zzz_yyy

List, Set and Tuple merging is purely additive, with no checks for uniqueness or already existing list items. E.g context [0,1,2] with contextMerge [2,3,4] will result in [0,1,2,2,3,4].

Keep this in mind especially where complex types like dicts nest inside a list - a merge will always add a new dict list item, not merge it into whatever dicts might exist on the list already.

See a worked example for contextmerge here.

3.4.2.5 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.

contextset and contextsetf overwrite existing keys. If you want to merge new values into an existing destination hierarchy, use pypyr.steps.contextmerge instead.

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

See a worked example for contextset here.

3.4.2.6 pypyr.steps.contextsetf

Set context keys from formatting expressions with Substitutions.

Requires the following context:

contextsetf:
  newkey: '{format expression}'
  newkey2: '{format expression}'

contextset and contextsetf overwrite existing keys. If you want to merge new values into an existing destination hierarchy, use pypyr.steps.contextmerge instead.

For example, say your context looks like this:

key1: value1
key2: value2
answer: 42

and your pipeline yaml looks like this:

steps:
  - name: pypyr.steps.contextsetf
    in:
      contextSetf:
        key2: any old value without a substitution - it will be a string now.
        key4: 'What do you get when you multiply six by nine? {answer}'

This will result in context like this:

key1: value1
key2: any old value without a substitution - it will be a string now.
answer: 42
key4: 'What do you get when you multiply six by nine? 42'

See a worked example for contextsetf here.

3.4.2.7 pypyr.steps.default

Sets values in context if they do not exist already. Does not overwrite existing values. Supports nested hierarchies.

This is especially useful for setting default values in context, for example when using optional arguments. from the shell.

This step sets the contents of the context key defaults into context where keys in defaults do not exist in context already. The contents of the defaults key must be a dictionary.

Example: Given a context like this:

key1: value1
key2:
    key2.1: value2.1
key3: None

And defaults input like this:

key1: updated value here won't overwrite since it already exists
key2:
    key2.2: value2.2
key3: key 3 exists so I won't overwrite

Will result in context:

key1: value1
key2:
    key2.1: value2.1
    key2.2: value2.2
key3: None

By comparison, the in step decorator, and the steps contextset, contextsetf and contextmerge overwrite values that are in context already.

The recursive if-not-exists-then-set check happens for dictionaries, but not for items in Lists, Sets and Tuples. You can set default values of type List, Set or Tuple if their keys don’t exist in context already, but this step will not recurse through the List, Set or Tuple itself.

Supports Substitutions. String interpolation applies to keys and values.

See a worked example for default here.

3.4.2.8 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 mypipeline "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 look-ma-no-params

Supports Substitutions.

3.4.2.9 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.

3.4.2.9.1 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>>

3.4.2.9.2 envSet

Set $ENVs from the pypyr context.

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

Values are strings to write to $ENV. You can use {key} Substitutions to format the string from context. 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: before_{key3}_after
    MYVAR3: arbtexthere

This will result in the following $ENVs:

$MYVAR1 = value1
$MYVAR2 = before_value3_after
$MYVAR3 = arbtexthere

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.

3.4.2.9.3 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

3.4.2.10 pypyr.steps.fetchjson

Loads a json file into the pypyr context.

This step requires the following key in the pypyr context to succeed:

fetchJsonPath. - path-like. Path to file on disk. Can be relative. Supports Substitutions.

Json parsed from the file will be merged into the pypyr context. This will overwrite existing values if the same keys are already in there.

I.e if file json has {'eggs' : 'boiled'}, but context {'eggs': 'fried'} already exists, returned context['eggs'] will be ‘boiled’.

The json should not be an array [] at the top level, but rather an Object.

3.4.2.11 pypyr.steps.fetchyaml

Loads a yaml file into the pypyr context.

This step requires the following key in the pypyr context to succeed:

fetchYamlPath. - path-like. Path to file on disk. Can be relative. Supports Substitutions.

Yaml parsed from the file will be merged into the pypyr context. This will overwrite existing values if the same keys are already in there.

I.e if file yaml has

eggs: boiled

but context {'eggs': 'fried'} already exists, returned context['eggs'] will be ‘boiled’.

The yaml should not be a list at the top level, but rather a mapping.

So the top-level yaml should not look like this:

- eggs
- ham

but rather like this:

breakfastOfChampions:
  - eggs
  - ham

3.4.2.12 pypyr.steps.fileformat

Parses input text file and substitutes {tokens} in the text of the file from the pypyr context.

The following context keys expected:

fileFormatIn
- Path to source file on disk.
fileFormatOut
- Write output file to here. Will create directories in path if these do not exist already.

So if you had a text file like this:

{k1} sit thee down and write
In a book that all may {k2}

And your pypyr context were:

k1: pypyr
k2: read

You would end up with an output file like this:

pypyr sit thee down and write
In a book that all may read

The file in and out paths support Substitutions.

3.4.2.13 pypyr.steps.fileformatjson

Parses input json file and substitutes {tokens} from the pypyr context.

Pretty much does the same thing as pypyr.steps.fileformat, only it makes it easier to work with curly braces for substitutions without tripping over the json’s structural braces.

The following context keys expected:

fileFormatJsonIn
- Path to source file on disk.
fileFormatJsonOut
- Write output file to here. Will create directories in path if these do not exist already.

Substitutions enabled for keys and values in the source json.

The file in and out paths also support Substitutions.

3.4.2.14 pypyr.steps.fileformatyaml

Parses input yaml file and substitutes {tokens} from the pypyr context.

Pretty much does the same thing as pypyr.steps.fileformat, only it makes it easier to work with curly braces for substitutions without tripping over the yaml’s structural braces. If your yaml doesn’t use curly braces that aren’t meant for {token} substitutions, you can happily use pypyr.steps.fileformat instead - it’s more memory efficient.

This step does not preserve comments. Use pypyr.steps.fileformat if you need to preserve comments on output.

The following context keys expected:

fileFormatYamlIn
- Path to source file on disk.
fileFormatYamlOut
- Write output file to here. Will create directories in path if these do not exist already.

The file in and out paths support Substitutions.

See a worked example of fileformatyaml.

3.4.2.15 pypyr.steps.filereplace

Parses input text file and replaces a search string.

The other fileformat steps, by way of contradistinction, uses string formatting expressions inside {braces} to format values against the pypyr context. This step, however, let’s you specify any search string and replace it with any replace string. This is handy if you are in a file where curly braces aren’t helpful for a formatting expression - e.g inside a .js file.

The following context keys expected:

fileReplaceIn
- Path to source file on disk.
fileReplaceOut
- Write output file to here. Will create directories in path if these do not exist already.
fileReplacePairs
- dictionary where format is:
  - ‘find_string’: ‘replace_string’

Example input context:

fileReplaceIn: ./infile.txt
fileReplaceOut: ./outfile.txt
fileReplacePairs:
  findmestring: replacewithme
  findanotherstring: replacewithanotherstring
  alaststring: alastreplacement

This also does string substitutions from context on the fileReplacePairs. It does this before it search & replaces the fileReplaceIn file.

Be careful of order. The last string replacement expression could well replace a replacement that an earlier replacement made in the sequence.

If fileReplacePairs is not an ordered collection, replacements could evaluate in any given order. If you are creating your in parameters in the pipeline yaml, don’t worry about it, it will be an ordered dictionary already, so life is good.

The file in and out paths support Substitutions.

See a worked example here.

3.4.2.16 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)

3.4.2.17 pypyr.steps.pype

3.4.2.17.1 Overview

Run another pipeline from this step. This allows pipelines to invoke other pipelines. Why pype? Because the pypyr can pipe that song again.

pype is handy if you want to split a larger, cumbersome pipeline into smaller units. This helps testing, in that you can test smaller units as separate pipelines without having to re-run the whole pipeline each time. This gets pretty useful for longer running sequences where the first steps are not idempotent but you do want to iterate over the last steps in the pipeline. Provisioning or deployment scripts frequently have this sort of pattern: where the first steps provision expensive resources in the environment and later steps just tweak settings on the existing environment.

The parent pipeline is the current, executing pipeline. The invoked, or child, pipeline is the pipeline you are calling from this step.

See here for worked example of pype.

3.4.2.17.2 Context properties

Example input context:

pype:
  name: 'pipeline name' # mandatory. string.
  pipeArg: 'argument here' # optional. string.
  raiseError: True # optional. bool. Defaults True.
  skipParse: True # optional. bool. Defaults True.
  useParentContext: True  # optional. bool. Defaults True.

pype property	description
name	Name of child pipeline to execute. This {name}.yaml must exist in the working directory/pipelines dir.
pipeArg	String to pass to the child pipeline context_parser. Equivalent to context arg on the pypyr cli. Only used if skipParse==False
raiseError	If True, errors in child raised up to parent. If False, log and swallow any errors that happen during the invoked pipeline’s execution. Swallowing means that the current/parent pipeline will carry on with the next step even if an error occurs in the invoked pipeline.
skipParse	If True, skip the context_parser on the invoked pipeline. This is relevant if your child-pipeline uses a context_parser to initialize context when you test it in isolation by running it directly from the cli, but when calling from a parent pipeline the parent is responsible for creating the appropriate context.
useParentContext	If True, passes the parent’s context to the child. Any changes to the context by the child will be available to the parent when the child completes. If False, the child creates its own, fresh context that does not contain any of the parent’s keys. The child’s context is destroyed upon completion of the child pipeline and updates to the child context do not reach the parent context.

3.4.2.17.3 Recursion

Yes, you can pype recursively - i.e a child pipeline can call its antecedents. It’s up to you to avoid infinite recursion, though. Since we’re all responsible adults here, pypyr does not protect you from infinite recursion other than the default python recursion limit. So don’t come crying if you blew your stack. Or a seal.

Here is a worked example of pype recursion.

3.4.2.18 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

3.4.2.19 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.

Supports string Substitutions.

Example pipeline yaml:

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

See a worked example for shell power here.

3.4.2.20 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 change directory during this shell step using cd, but dir changes are only in scope for subsequent commands in this step, not for subsequent steps:

- name: pypyr.steps.shell
  description: hop one up from current working dir
  in:
    cmd: '[sic]"echo ${PWD}; cd ../; echo ${PWD}"'
- name: pypyr.steps.shell
  description: back to your current working dir
  in:
    cmd: '[sic]"echo ${PWD}"'

Supports string Substitutions.

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;
  - name: pypyr.steps.shell
    description: if you want to pass curlies to the shell, use sic strings
    in:
      cmd: '[sic]"echo ${PWD};"'

See a worked example for shell power here.

3.4.2.21 pypyr.steps.tar

Archive and/or extract tars with or without compression.

At least one of these context keys must exist:

tarExtract
tarArchive

Optionally, you can also specify the tar compression format with context['tarFormat']. If not specified, defaults to lzma/xz Available options:

‘’ - no compression
gz (gzip)
bz2 (bzip2)
xz (lzma)

This step will run whatever combination of Extract and Archive you specify. Regardless of combination, execution order is Extract, Archive.

Never extract archives from untrusted sources without prior inspection. It is possible that files are created outside of path, e.g. members that have absolute filenames starting with “/” or filenames with two dots “..”.

See a worked example for tar here.

3.4.2.21.1 tarExtract

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

keys are the path to the tar to extract.

values are the destination paths.

You can use {key} substitutions to format the string from context. See Substitutions.

key1: here
key2: tar.xz
tarExtract:
  - in: path/to/my.tar.xz
    out: /path/extract/{key1}
  - in: another/{key2}
    out: .

This will:

Extract path/to/my.tar.xz to /path/extract/here
Extract another/tar.xz to the current execution directory
- This is the directory you’re running pypyr from, not the pypyr pipeline working directory you set with the --dir flag.

3.4.2.21.2 tarArchive

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

keys are the paths to archive.

values are the destination output paths.

You can use {key} substitutions to format the string from context. See Substitutions.

key1: destination.tar.xz
key2: value2
tarArchive:
  - in: path/{key2}/dir
    out: path/to/{key1}
  - in: another/my.file
    out: ./my.tar.xz

This will:

Archive directory path/value2/dir to path/to/destination.tar.xz,
Archive file another/my.file to ./my.tar.xz

3.4.3 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 Substitutions

4.1 string interpolation

You can use substitution tokens, aka string interpolation, where specified for context items. This substitutes anything between {curly braces} with the context value for that key. This also works where you have dictionaries/lists inside dictionaries/lists. For example, if your context looked like this:

key1: down
key2: valleys
key3: value3
key4: "Piping {key1} the {key2} wild"

The value for key4 will be “Piping down the valleys wild”.

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

In json & yaml, curlies need to be inside quotes to make sure they parse as strings. Especially watch in .yaml, where { as the first character of a key or value will throw a formatting error if it’s not in quotes like this: “{key}”

You can also reference keys nested deeper in the context hierarchy, in cases where you have a dictionary that contains lists/dictionaries that might contain other lists/dictionaries and so forth.

root:
  - list index 0
  - key1: this is a value from a dict containing a list, which contains a dict at index 1
    key2: key 2 value
  - list index 1

Given the context above, you can use formatting expressions to access nested values like this:

'{root[0]}' = list index 0
'{root[1][key1]}' = this is a value from a dict containing a list, which contains a dict at index 1
'{root[1][key2]}' = key 2 value
'{root[2]}' = list index 1

4.2 sic strings

If a string is NOT to have {substitutions} run on it, it’s sic erat scriptum, or sic for short. This is handy especially when you are dealing with json as a string, rather than an actual json object, so you don’t have to double curly all the structural braces.

A sic string looks like this:

[sic]"<<your string literal here>>"

For example:

[sic]"piping {key} the valleys wild"

Will return “piping {key} the valleys wild” without attempting to substitute {key} from context. You can happily use “, ‘ or {} inside a [sic]"" string without escaping these any further. This makes sic strings ideal for strings containing json.

In pipeline yaml, you need to have the [sic] in single quotes or as part of a literal block:

- name: pypyr.steps.echo
  description: >
              use a sic string not to format any {values}. Do watch the
              use of the yaml literal with block chomping indicator |- to
              prevent the last character in the string from being a LF. If
              you don't do this, you will end up with the trailing " in your
              output, which in this case would be malformed json.
  in:
    echoMe: |-
            [sic]"
            {
              "key1": "key1 value with a {curly}"
            }"
- name: pypyr.steps.echo
  description: put sic string in single quotes
  in:
    echoMe: '[sic]"string with a {curly} with ", '' and & and double quote at end:""'

See a worked example for substitutions here.

5 Plug-Ins

The pypyr core is deliberately kept light so the dependencies are down to the minimum. I loathe installs where there're a raft of extra deps that I don't use clogging up the system.

Where other libraries are requisite, you can selectively choose to add this functionality by installing a pypyr plug-in.

boss pypyr plug-ins	description
pypyr-aws	Interact with the AWS sdk api. Supports all AWS Client functions, such as S3, EC2, ECS & co. via the AWS low-level Client API.
pypyr-slack	Send messages to Slack

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