# 2.5.12. Properties

Build properties are a generalized way to provide configuration information to build steps; see Build Properties for the conceptual overview of properties.

Some build properties come from external sources and are set before the build begins; others are set during the build and are available for later steps. The sources for properties are:

`global configuration`

  These properties apply to all builds.

schedulers

  A scheduler can specify properties that become available to all builds it starts.

changes

  A change can have properties attached to it, supplying extra information gathered by the change source. This is most commonly used with the `sendchange` command.

forced builds

  The “Force Build” form allows users to specify properties

`workers`

  A worker can pass properties on to the builds it performs.

builds

  A build automatically sets a number of properties on itself.

`builders`

  A builder can set properties on all the builds it runs.

steps

  The steps of a build can set properties that are available to subsequent steps. In particular, source steps set the got_revision property.

If the same property is supplied in multiple places, the final appearance takes precedence. For example, a property set in a builder configuration will override the one supplied by the scheduler.

Properties are stored internally in JSON format, so they are limited to basic types of data: numbers, strings, lists, and dictionaries.

## 2.5.12.1. Common Build Properties

The following build properties are set when the build is started, and are available to all steps.

`got_revision`

  This property is set when a `Source` step checks out the source tree, and provides the revision that was actually obtained from the VC system. In general this should be the same as `revision`, except for non-absolute sourcestamps, where `got_revision` indicates what revision was current when the checkout was performed. This can be used to rebuild the same source code later.

  Note

  For some VC systems (Darcs in particular), the revision is a large string containing newlines, and is not suitable for interpolation into a filename.

  For multi-codebase builds (where codebase is not the default ‘’), this property is a dictionary, keyed by codebase.

`buildername`

  This is a string that indicates which `Builder` the build was a part of. The combination of buildername and buildnumber uniquely identify a build.

`builderid`

  This is a number that indicates which `Builder` the build was a part of.

`buildnumber`

  Each build gets a number, scoped to the `Builder` (so the first build performed on any given `Builder` will have a build number of 0). This integer property contains the build’s number.

`workername`

  This is a string which identifies which worker the build is running on.

`scheduler`

  If the build was started from a scheduler, then this property will contain the name of that scheduler.

`builddir`

  The absolute path of the base working directory on the worker of the current builder.

For single codebase builds, where the codebase is ‘’, the following Source Stamp Attributes are also available as properties: `branch`, `revision`, `repository`, and `project` .

## 2.5.12.2. Source Stamp Attributes

`branch` `revision` `repository` `project` `codebase`

> For details of these attributes see Concepts.

`changes`

> This attribute is a list of dictionaries representing the changes that make up this sourcestamp.

## 2.5.12.3. Using Properties in Steps

For the most part, properties are used to alter the behavior of build steps during a build. This is done by using renderables (objects implementing the `IRenderable` interface) as step parameters. When the step is started, each such object is rendered using the current values of the build properties, and the resultant rendering is substituted as the actual value of the step parameter.

Buildbot offers several renderable object types covering common cases. It’s also possible to create custom renderables.

Note

Properties are defined while a build is in progress; their values are not available when the configuration file is parsed. This can sometimes confuse newcomers to Buildbot! In particular, the following is a common error:

    if Property('release_train') == 'alpha':
        f.addStep(...)

This does not work because the value of the property is not available when the `if` statement is executed. However, Python will not detect this as an error - you will just never see the step added to the factory.

You can use renderables in most step parameters. Please file bugs for any parameters which do not accept renderables.

### Property

The simplest renderable is `Property`, which renders to the value of the property named by its argument:

    from buildbot.plugins import steps, util

    f.addStep(steps.ShellCommand(command=['echo', 'buildername:',
                                 util.Property('buildername')]))

You can specify a default value by passing a `default` keyword argument:

    f.addStep(steps.ShellCommand(command=['echo', 'warnings:',
                                 util.Property('warnings', default='none')]))

The default value is used when the property doesn’t exist, or when the value is something Python regards as `False`. The `defaultWhenFalse` argument can be set to `False` to force Buildbot to use the default argument only if the parameter is not set:

    f.addStep(steps.ShellCommand(command=['echo', 'warnings:',
                                 util.Property('warnings', default='none',
                                               defaultWhenFalse=False)]))

The default value can be a renderable itself, e.g.,

    command=util.Property('command', default=util.Property('default-command'))

### Interpolate

`Property` can only be used to replace an entire argument: in the example above, it replaces an argument to `echo`. Often, properties need to be interpolated into strings, instead. The tool for that job is Interpolate.

The more common pattern is to use Python dictionary-style string interpolation by using the `%(prop:<propname>)s` syntax. In this form, the property name goes in the parentheses, as above. A common mistake is to omit the trailing “s”, leading to a rather obscure error from Python (“ValueError: unsupported format character”).

    from buildbot.plugins import steps, util
    f.addStep(steps.ShellCommand(
        command=['make',
                util.Interpolate('REVISION=%(prop:got_revision)s'),
                'dist']))

This example will result in a `make` command with an argument like `REVISION=12098`.

The syntax of dictionary-style interpolation is a selector, followed by a colon, followed by a selector specific key, optionally followed by a colon and a string indicating how to interpret the value produced by the key.

The following selectors are supported.

`prop`

  The key is the name of a property.

`src`

  The key is a codebase and source stamp attribute, separated by a colon. Note, the syntax is `%(src:<codebase>:<ssattr>)s`, which differs from other selectors.

`kw`

  The key refers to a keyword argument passed to `Interpolate`. Those keyword arguments may be ordinary values or renderables.

`secret`

  The key refers to a secret provided by a provider declared in `secretsProviders` .

`worker`

  The key refers to an info item provided by `workers`.

The following ways of interpreting the value are available.

`-replacement`

  If the key exists, substitute its value; otherwise, substitute `replacement`. `replacement` may be empty (default), `%(prop:propname:-)s`.

`~replacement`

  Like `-replacement`, but only substitutes the value of the key if it is something Python regards as `True`. Python considers `None`, 0, empty lists, and the empty string to be false, so such values will be replaced by `replacement`.

`+replacement`

  If the key exists, substitute `replacement`; otherwise, substitute an empty string.

`?|sub_if_exists|sub_if_missing`

`#?|sub_if_true|sub_if_false`

  Ternary substitution, depending on either the key being present (with `?`, similar to `+`) or being `True` (with `#?`, like `~`). Notice that there is a pipe immediately following the question mark and between the two substitution alternatives. The character that follows the question mark is used as the delimiter between the two alternatives. In the above examples, it is a pipe, but any character other than `(` can be used.

Note

Although these are similar to shell substitutions, no other substitutions are currently supported.

Example:

    from buildbot.plugins import steps, util
    f.addStep(steps.ShellCommand(
        command=[
            'save-build-artifacts-script.sh',
            util.Interpolate('-r %(prop:repository)s'),
            util.Interpolate('-b %(src::branch)s'),
            util.Interpolate('-d %(kw:data)s', data="some extra needed data")
        ]))

Note

We use `%(src::branch)s` in most examples, because `codebase` is empty by default.

Example:

    from buildbot.plugins import steps, util
    f.addStep(steps.ShellCommand(
        command=[
            'make',
            util.Interpolate('REVISION=%(prop:got_revision:-%(src::revision:-unknown)s)s'),
            'dist'
        ]))

In addition, `Interpolate` supports using positional string interpolation. Here, `%s` is used as a placeholder, and the substitutions (which may be renderables) are given as subsequent arguments:

    f.addStep(steps.ShellCommand(
        command=[
            'echo',
            util.Interpolate('%d warnings and %d errors',
                             util.Property('warnings'),
                             util.Property('errors'))
        ]))

Note

Like Python, you can use either positional interpolation or dictionary-style interpolation, but not both. Thus you cannot use a string like `Interpolate("foo-%(src::revision)s-%s", "branch")`.

### Renderer

While Interpolate can handle many simple cases, and even some common conditionals, more complex cases are best handled with Python code. The `renderer` decorator creates a renderable object whose rendering is obtained by calling the decorated function when the step to which it’s passed begins. The function receives an `IProperties` object, which it can use to examine the values of any and all properties. For example:

    from buildbot.plugins import steps, util

    @util.renderer
    def makeCommand(props):
        command = ['make']
        cpus = props.getProperty('CPUs')
        if cpus:
            command.extend(['-j', str(cpus+1)])
        else:
            command.extend(['-j', '2'])
        command.extend([util.Interpolate('%(prop:MAKETARGET)s')])
        return command

    f.addStep(steps.ShellCommand(command=makeCommand))

You can think of `renderer` as saying “call this function when the step starts”.

Note

Since 0.9.3, renderer can itself return `IRenderable` objects or containers containing `IRenderable`.

Optionally, extra arguments may be passed to the rendered function at any time by calling `withArgs` on the renderable object. The `withArgs` method accepts `*args` and `**kwargs` arguments which are stored in a new renderable object which is returned. The original renderable object is not modified. Multiple `withArgs` calls may be chained. The passed `*args` and `**kwargs` parameters are rendered and the results are passed to the rendered function at the time it is itself rendered. For example:

    from buildbot.plugins import steps, util

    @util.renderer
    def makeCommand(props, target):
        command = ['make']
        cpus = props.getProperty('CPUs')
        if cpus:
            command.extend(['-j', str(cpus+1)])
        else:
            command.extend(['-j', '2'])
        command.extend([target])
        return command

    f.addStep(steps.ShellCommand(command=makeCommand.withArgs('mytarget')))

Note

The rendering of the renderable object may happen at unexpected times, so it is best to ensure that the passed extra arguments are not changed.

Note

Config errors with Renderables may not always be caught via checkconfig.

### Transform

`Transform` is an alternative to `renderer`. While `renderer` is useful for creating new renderables, `Transform` is easier to use when you want to transform or combine the renderings of preexisting renderables.

`Transform` takes a function and any number of positional and keyword arguments. The function must either be a callable object or a renderable producing one. When rendered, a `Transform` first replaces all of its arguments that are renderables with their renderings, then calls the function, passing it the positional and keyword arguments, and returns the result as its own rendering.

For example, suppose `my_path` is a path on the worker, and you want to get it relative to the build directory. You can do it like this:

    import os.path
    from buildbot.plugins import util

    my_path_rel = util.Transform(os.path.relpath, my_path, start=util.Property('builddir'))

This works whether `my_path` is an ordinary string or a renderable. `my_path_rel` will be a renderable in either case, however.

### FlattenList

If a nested list should be flattened for some renderables, FlattenList can be used. For example:

    from buildbot.plugins import steps, util
    f.addStep(steps.ShellCommand(
        command=[ 'make' ],
        descriptionDone=util.FlattenList([ 'make ', [ 'done' ]])
    ))

`descriptionDone` will be set to `[ 'make', 'done' ]` when the `ShellCommand` executes. This is useful when a list-returning property is used in renderables.

Note

ShellCommand automatically flattens nested lists in its `command` argument, so there is no need to use `FlattenList` for it.

### WithProperties

Warning

This class is deprecated. It is an older version of Interpolate. It exists for compatibility with older configs.

The simplest use of this class is with positional string interpolation. Here, `%s` is used as a placeholder, and property names are given as subsequent arguments:

    from buildbot.plugins import steps, util
    f.addStep(steps.ShellCommand(
        command=["tar", "czf",
                util.WithProperties("build-%s-%s.tar.gz", "branch", "revision"),
                "source"]))

If this `BuildStep` were used in a tree obtained from Git, it would create a tarball with a name like `build-master-a7d3a333db708e786edb34b6af646edd8d4d3ad9.tar.gz`.

The more common pattern is to use Python dictionary-style string interpolation by using the `%(propname)s` syntax. In this form, the property name goes in the parentheses, as above. A common mistake is to omit the trailing “s”, leading to a rather obscure error from Python (“ValueError: unsupported format character”).

    from buildbot.plugins import steps, util
    f.addStep(steps.ShellCommand(
        command=['make',
                util.WithProperties('REVISION=%(got_revision)s'),
                'dist']))

This example will result in a `make` command with an argument like `REVISION=12098`.

The dictionary-style interpolation supports a number of more advanced syntaxes in the parentheses.

`propname:-replacement`

  If `propname` exists, substitute its value; otherwise, substitute `replacement`. `replacement` may be empty (`%(propname:-)s`)

`propname:~replacement`

  Like `propname:-replacement`, but only substitutes the value of property `propname` if it is something Python regards as `True`. Python considers `None`, 0, empty lists, and the empty string to be false, so such values will be replaced by `replacement`.

`propname:+replacement`

  If `propname` exists, substitute `replacement`; otherwise, substitute an empty string.

Although these are similar to shell substitutions, no other substitutions are currently supported, and `replacement` in the above cannot contain more substitutions.

Note: like Python, you can use either positional interpolation or dictionary-style interpolation, not both. Thus you cannot use a string like `WithProperties("foo-%(revision)s-%s", "branch")`.

### Custom Renderables

If the options described above are not sufficient, more complex substitutions can be achieved by writing custom renderables.

The `IRenderable` interface is simple - objects must provide a getRenderingFor method. The method should take one argument - an `IProperties` provider - and should return the rendered value or a deferred firing with one. You can pass instances of the class anywhere other renderables are accepted. For example:

    import time
    from buildbot.interfaces import IRenderable
    from zope.interface import implementer

    @implementer(IRenderable)
    class DetermineFoo(object):
        def getRenderingFor(self, props):
            if props.hasProperty('bar'):
                return props['bar']
            elif props.hasProperty('baz'):
                return props['baz']
            return 'qux'
    ShellCommand(command=['echo', DetermineFoo()])

or, more practically,

    from buildbot.interfaces import IRenderable
    from zope.interface import implementer
    from buildbot.plugins import util

    @implementer(IRenderable)
    class Now(object):
        def getRenderingFor(self, props):
            return time.clock()
    ShellCommand(command=['make', util.Interpolate('TIME=%(kw:now)s', now=Now())])

This is equivalent to:

    from buildbot.plugins import util

    @util.renderer
    def now(props):
        return time.clock()
    ShellCommand(command=['make', util.Interpolate('TIME=%(kw:now)s', now=now)])

Note that a custom renderable must be instantiated (and its constructor can take whatever arguments you like), whereas a function decorated with `renderer` can be used directly.

### URL for build

Its common to need to use the URL for the build in a step. For this, you can use a special custom renderer as following:

    from buildbot.plugins import *

    ShellCommand(command=['make', util.Interpolate('BUILDURL=%(kw:url)s', url=util.URLForBuild)])

### Renderable Comparison

Its common to need to make basic comparison or calculation with properties. The `Property` and `Interpolate` objects contain necessary operator overloads to make this possible.

    from buildbot.plugins import *

    ShellCommand(command=['make'], doStepIf=Interpolate("worker:os_id")  == 'ubuntu')

In previous code, the value of the comparison can only be computed at runtime, so the result of the comparison is actually a renderable which will be computed at the start of the step.

    from buildbot.plugins import *

    ShellCommand(command=['make'], doStepIf=Interpolate("worker:os_id").in_(['debian', 'ubuntu']))

‘in’ operator cannot be overloaded, so we add a simple `in_` method to `Property` and `Interpolate`.

Currently supported operators are `in_`, `==`, `!=`, `<`, `<=`, `>`, `>=`, `+`, `-`, `*`, `/`, `//`, `%`.