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|
<?xml version='1.0'?>
<!DOCTYPE sconsdoc [
<!ENTITY % scons SYSTEM "../scons.mod">
%scons;
<!ENTITY % builders-mod SYSTEM "../generated/builders.mod">
%builders-mod;
<!ENTITY % functions-mod SYSTEM "../generated/functions.mod">
%functions-mod;
<!ENTITY % tools-mod SYSTEM "../generated/tools.mod">
%tools-mod;
<!ENTITY % variables-mod SYSTEM "../generated/variables.mod">
%variables-mod;
]>
<chapter id="chap-builders-writing"
xmlns="http://www.scons.org/dbxsd/v1.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.scons.org/dbxsd/v1.0 http://www.scons.org/dbxsd/v1.0/scons.xsd">
<title>Writing Your Own Builders</title>
<!--
__COPYRIGHT__
Permission is hereby granted, free of charge, to any person obtaining
a copy of this software and associated documentation files (the
"Software"), to deal in the Software without restriction, including
without limitation the rights to use, copy, modify, merge, publish,
distribute, sublicense, and/or sell copies of the Software, and to
permit persons to whom the Software is furnished to do so, subject to
the following conditions:
The above copyright notice and this permission notice shall be included
in all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY
KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE
WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
-->
<!--
=head2 Adding new methods
For slightly more demanding changes, you may wish to add new methods to the
C<cons> package. Here's an example of a very simple extension,
C<InstallScript>, which installs a tcl script in a requested location, but
edits the script first to reflect a platform-dependent path that needs to be
installed in the script:
# cons::InstallScript - Create a platform dependent version of a shell
# script by replacing string ``#!your-path-here'' with platform specific
# path $BIN_DIR.
sub cons::InstallScript {
my ($env, $dst, $src) = @_;
Command $env $dst, $src, qq(
sed s+your-path-here+$BIN_DIR+ %< > %>
chmod oug+x %>
);
}
Notice that this method is defined directly in the C<cons> package (by
prefixing the name with C<cons::>). A change made in this manner will be
globally visible to all environments, and could be called as in the
following example:
InstallScript $env "$BIN/foo", "foo.tcl";
For a small improvement in generality, the C<BINDIR> variable could be
passed in as an argument or taken from the construction environment-,-as
C<%BINDIR>.
=head2 Overriding methods
Instead of adding the method to the C<cons> name space, you could define a
new package which inherits existing methods from the C<cons> package and
overrides or adds others. This can be done using Perl's inheritance
mechanisms.
The following example defines a new package C<cons::switch> which
overrides the standard C<Library> method. The overridden method builds
linked library modules, rather than library archives. A new
constructor is provided. Environments created with this constructor
will have the new library method; others won't.
package cons::switch;
BEGIN {@ISA = 'cons'}
sub new {
shift;
bless new cons(@_);
}
sub Library {
my($env) = shift;
my($lib) = shift;
my(@objs) = Objects $env @_;
Command $env $lib, @objs, q(
%LD -r %LDFLAGS %< -o %>
);
}
This functionality could be invoked as in the following example:
$env = new cons::switch(@overrides);
...
Library $env 'lib.o', 'foo.c', 'bar.c';
-->
<para>
Although &SCons; provides many useful methods
for building common software products
(programs, libraries, documents, etc.),
you frequently want to be
able to build some other type of file
not supported directly by &SCons;.
Fortunately, &SCons; makes it very easy
to define your own &Builder; objects
for any custom file types you want to build.
(In fact, the &SCons; interfaces for creating
&Builder; objects are flexible enough and easy enough to use
that all of the the &SCons; built-in &Builder; objects
are created using the mechanisms described in this section.)
</para>
<section>
<title>Writing Builders That Execute External Commands</title>
<para>
The simplest &Builder; to create is
one that executes an external command.
For example, if we want to build
an output file by running the contents
of the input file through a command named
<literal>foobuild</literal>,
creating that &Builder; might look like:
</para>
<programlisting>
bld = Builder(action = 'foobuild < $SOURCE > $TARGET')
</programlisting>
<para>
All the above line does is create a free-standing
&Builder; object.
The next section will show us how to actually use it.
</para>
</section>
<section>
<title>Attaching a Builder to a &ConsEnv;</title>
<para>
A &Builder; object isn't useful
until it's attached to a &consenv;
so that we can call it to arrange
for files to be built.
This is done through the &cv-link-BUILDERS;
&consvar; in an environment.
The &cv-BUILDERS; variable is a Python dictionary
that maps the names by which you want to call
various &Builder; objects to the objects themselves.
For example, if we want to call the
&Builder; we just defined by the name
<function>Foo</function>,
our &SConstruct; file might look like:
</para>
<scons_example name="builderswriting_ex1">
<file name="SConstruct">
bld = Builder(action = 'foobuild < $SOURCE > $TARGET')
env = Environment(BUILDERS = {'Foo' : bld})
import os
env['ENV']['PATH'] = env['ENV']['PATH'] + os.pathsep + os.getcwd()
env.Foo('file.foo', 'file.input')
</file>
<file name="file.input">
file.input
</file>
<file name="foobuild" chmod="0755">
cat
</file>
</scons_example>
<sconstruct>
bld = Builder(action = 'foobuild < $SOURCE > $TARGET')
env = Environment(BUILDERS = {'Foo' : bld})
</sconstruct>
<para>
With the &Builder; attached to our &consenv;
with the name <function>Foo</function>,
we can now actually call it like so:
</para>
<programlisting>
env.Foo('file.foo', 'file.input')
</programlisting>
<para>
Then when we run &SCons; it looks like:
</para>
<scons_output example="builderswriting_ex1" suffix="1">
<scons_output_command>scons -Q</scons_output_command>
</scons_output>
<para>
Note, however, that the default &cv-BUILDERS;
variable in a &consenv;
comes with a default set of &Builder; objects
already defined:
&b-link-Program;, &b-link-Library;, etc.
And when we explicitly set the &cv-BUILDERS; variable
when we create the &consenv;,
the default &Builder;s are no longer part of
the environment:
</para>
<!--
The ToolSurrogate stuff that's used to capture output initializes
SCons.Defaults.ConstructionEnvironment with its own list of TOOLS.
In this next example, we want to show the user that when they
set the BUILDERS explicitly, the call to env.Program() generates
an AttributeError. This won't happen with all of the default
ToolSurrogates in the default construction environment. To make the
AttributeError show up, we have to overwite the default construction
environment's TOOLS variable so Program() builder doesn't show up.
We do this by executing a slightly different SConstruct file than the
one we print in the guide, with two extra statements at the front
that overwrite the TOOLS variable as described. Note that we have
to jam those statements on to the first line to keep the line number
in the generated error consistent with what the user will see in the
User's Guide.
-->
<scons_example name="builderswriting_ex2">
<file name="SConstruct">
import SCons.Defaults; SCons.Defaults.ConstructionEnvironment['TOOLS'] = {}; bld = Builder(action = 'foobuild < $SOURCE > $TARGET')
env = Environment(BUILDERS = {'Foo' : bld})
env.Foo('file.foo', 'file.input')
env.Program('hello.c')
</file>
<file name="SConstruct.printme" printme="1">
bld = Builder(action = 'foobuild < $SOURCE > $TARGET')
env = Environment(BUILDERS = {'Foo' : bld})
env.Foo('file.foo', 'file.input')
env.Program('hello.c')
</file>
<file name="file.input">
file.input
</file>
<file name="hello.c">
hello.c
</file>
</scons_example>
<scons_output example="builderswriting_ex2" suffix="1">
<scons_output_command>scons -Q</scons_output_command>
</scons_output>
<para>
To be able to use both our own defined &Builder; objects
and the default &Builder; objects in the same &consenv;,
you can either add to the &cv-BUILDERS; variable
using the &Append; function:
</para>
<scons_example name="builderswriting_ex3">
<file name="SConstruct">
env = Environment()
import os
env['ENV']['PATH'] = env['ENV']['PATH'] + os.pathsep + os.getcwd()
bld = Builder(action = 'foobuild < $SOURCE > $TARGET')
env.Append(BUILDERS = {'Foo' : bld})
env.Foo('file.foo', 'file.input')
env.Program('hello.c')
</file>
<file name="file.input">
file.input
</file>
<file name="hello.c">
hello.c
</file>
<file name="foobuild" chmod="0755">
cat
</file>
</scons_example>
<sconstruct>
env = Environment()
bld = Builder(action = 'foobuild < $SOURCE > $TARGET')
env.Append(BUILDERS = {'Foo' : bld})
env.Foo('file.foo', 'file.input')
env.Program('hello.c')
</sconstruct>
<para>
Or you can explicitly set the appropriately-named
key in the &cv-BUILDERS; dictionary:
</para>
<sconstruct>
env = Environment()
bld = Builder(action = 'foobuild < $SOURCE > $TARGET')
env['BUILDERS']['Foo'] = bld
env.Foo('file.foo', 'file.input')
env.Program('hello.c')
</sconstruct>
<para>
Either way, the same &consenv;
can then use both the newly-defined
<function>Foo</function> &Builder;
and the default &b-link-Program; &Builder;:
</para>
<scons_output example="builderswriting_ex3" suffix="1">
<scons_output_command>scons -Q</scons_output_command>
</scons_output>
</section>
<section>
<title>Letting &SCons; Handle The File Suffixes</title>
<para>
By supplying additional information
when you create a &Builder;,
you can let &SCons; add appropriate file
suffixes to the target and/or the source file.
For example, rather than having to specify
explicitly that you want the <literal>Foo</literal>
&Builder; to build the <literal>file.foo</literal>
target file from the <literal>file.input</literal> source file,
you can give the <literal>.foo</literal>
and <literal>.input</literal> suffixes to the &Builder;,
making for more compact and readable calls to
the <literal>Foo</literal> &Builder;:
</para>
<scons_example name="builderswriting_ex4">
<file name="SConstruct">
bld = Builder(action = 'foobuild < $SOURCE > $TARGET',
suffix = '.foo',
src_suffix = '.input')
env = Environment(BUILDERS = {'Foo' : bld})
import os
env['ENV']['PATH'] = env['ENV']['PATH'] + os.pathsep + os.getcwd()
env.Foo('file1')
env.Foo('file2')
</file>
<file name="file1.input">
file1.input
</file>
<file name="file2.input">
file2.input
</file>
<file name="foobuild" chmod="0755">
cat
</file>
</scons_example>
<sconstruct>
bld = Builder(action = 'foobuild < $SOURCE > $TARGET',
suffix = '.foo',
src_suffix = '.input')
env = Environment(BUILDERS = {'Foo' : bld})
env.Foo('file1')
env.Foo('file2')
</sconstruct>
<scons_output example="builderswriting_ex4" suffix="1">
<scons_output_command>scons -Q</scons_output_command>
</scons_output>
<para>
You can also supply a <literal>prefix</literal> keyword argument
if it's appropriate to have &SCons; append a prefix
to the beginning of target file names.
</para>
</section>
<section>
<title>Builders That Execute Python Functions</title>
<para>
In &SCons;, you don't have to call an external command
to build a file.
You can, instead, define a Python function
that a &Builder; object can invoke
to build your target file (or files).
Such a &buildfunc; definition looks like:
</para>
<programlisting>
def build_function(target, source, env):
# Code to build "target" from "source"
return None
</programlisting>
<para>
The arguments of a &buildfunc; are:
</para>
<variablelist>
<varlistentry>
<term>target</term>
<listitem>
<para>
A list of Node objects representing
the target or targets to be
built by this builder function.
The file names of these target(s)
may be extracted using the Python &str; function.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>source</term>
<listitem>
<para>
A list of Node objects representing
the sources to be
used by this builder function to build the targets.
The file names of these source(s)
may be extracted using the Python &str; function.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>env</term>
<listitem>
<para>
The &consenv; used for building the target(s).
The builder function may use any of the
environment's construction variables
in any way to affect how it builds the targets.
</para>
</listitem>
</varlistentry>
</variablelist>
<para>
The builder function must
return a <literal>0</literal> or <literal>None</literal> value
if the target(s) are built successfully.
The builder function
may raise an exception
or return any non-zero value
to indicate that the build is unsuccessful,
</para>
<para>
Once you've defined the Python function
that will build your target file,
defining a &Builder; object for it is as
simple as specifying the name of the function,
instead of an external command,
as the &Builder;'s
<literal>action</literal>
argument:
</para>
<scons_example name="builderswriting_ex5">
<file name="SConstruct" printme="1">
def build_function(target, source, env):
# Code to build "target" from "source"
return None
bld = Builder(action = build_function,
suffix = '.foo',
src_suffix = '.input')
env = Environment(BUILDERS = {'Foo' : bld})
env.Foo('file')
</file>
<file name="file.input">
file.input
</file>
</scons_example>
<para>
And notice that the output changes slightly,
reflecting the fact that a Python function,
not an external command,
is now called to build the target file:
</para>
<scons_output example="builderswriting_ex5" suffix="1">
<scons_output_command>scons -Q</scons_output_command>
</scons_output>
</section>
<section>
<title>Builders That Create Actions Using a &Generator;</title>
<para>
&SCons; Builder objects can create an action "on the fly"
by using a function called a &generator;.
This provides a great deal of flexibility to
construct just the right list of commands
to build your target.
A &generator; looks like:
</para>
<programlisting>
def generate_actions(source, target, env, for_signature):
return 'foobuild < %s > %s' % (target[0], source[0])
</programlisting>
<para>
The arguments of a &generator; are:
</para>
<variablelist>
<varlistentry>
<term>source</term>
<listitem>
<para>
A list of Node objects representing
the sources to be built
by the command or other action
generated by this function.
The file names of these source(s)
may be extracted using the Python &str; function.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>target</term>
<listitem>
<para>
A list of Node objects representing
the target or targets to be built
by the command or other action
generated by this function.
The file names of these target(s)
may be extracted using the Python &str; function.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>env</term>
<listitem>
<para>
The &consenv; used for building the target(s).
The generator may use any of the
environment's construction variables
in any way to determine what command
or other action to return.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>for_signature</term>
<listitem>
<para>
A flag that specifies whether the
generator is being called to contribute to a build signature,
as opposed to actually executing the command.
<!-- XXX NEED MORE HERE, describe generators use in signatures -->
</para>
</listitem>
</varlistentry>
</variablelist>
<para>
The &generator; must return a
command string or other action that will be used to
build the specified target(s) from the specified source(s).
</para>
<para>
Once you've defined a &generator;,
you create a &Builder; to use it
by specifying the generator keyword argument
instead of <literal>action</literal>.
</para>
<scons_example name="builderswriting_ex6">
<file name="SConstruct">
def generate_actions(source, target, env, for_signature):
return 'foobuild < %s > %s' % (source[0], target[0])
bld = Builder(generator = generate_actions,
suffix = '.foo',
src_suffix = '.input')
env = Environment(BUILDERS = {'Foo' : bld})
import os
env['ENV']['PATH'] = env['ENV']['PATH'] + os.pathsep + os.getcwd()
env.Foo('file')
</file>
<file name="file.input">
file.input
</file>
<file name="foobuild" chmod="0755">
cat
</file>
</scons_example>
<sconstruct>
def generate_actions(source, target, env, for_signature):
return 'foobuild < %s > %s' % (source[0], target[0])
bld = Builder(generator = generate_actions,
suffix = '.foo',
src_suffix = '.input')
env = Environment(BUILDERS = {'Foo' : bld})
env.Foo('file')
</sconstruct>
<scons_output example="builderswriting_ex6" suffix="1">
<scons_output_command>scons -Q</scons_output_command>
</scons_output>
<para>
Note that it's illegal to specify both an
<literal>action</literal>
and a
<literal>generator</literal>
for a &Builder;.
</para>
</section>
<section>
<title>Builders That Modify the Target or Source Lists Using an &Emitter;</title>
<para>
&SCons; supports the ability for a Builder to modify the
lists of target(s) from the specified source(s).
You do this by defining an &emitter; function
that takes as its arguments
the list of the targets passed to the builder,
the list of the sources passed to the builder,
and the construction environment.
The emitter function should return the modified
lists of targets that should be built
and sources from which the targets will be built.
</para>
<para>
For example, suppose you want to define a Builder
that always calls a <filename>foobuild</filename> program,
and you want to automatically add
a new target file named
<filename>new_target</filename>
and a new source file named
<filename>new_source</filename>
whenever it's called.
The &SConstruct; file might look like this:
</para>
<scons_example name="builderswriting_ex7">
<file name="SConstruct">
def modify_targets(target, source, env):
target.append('new_target')
source.append('new_source')
return target, source
bld = Builder(action = 'foobuild $TARGETS - $SOURCES',
suffix = '.foo',
src_suffix = '.input',
emitter = modify_targets)
env = Environment(BUILDERS = {'Foo' : bld})
import os
env['ENV']['PATH'] = env['ENV']['PATH'] + os.pathsep + os.getcwd()
env.Foo('file')
</file>
<file name="file.input">
file.input
</file>
<file name="new_source">
new_source
</file>
<file name="foobuild" chmod="0755">
cat
</file>
</scons_example>
<sconstruct>
def modify_targets(target, source, env):
target.append('new_target')
source.append('new_source')
return target, source
bld = Builder(action = 'foobuild $TARGETS - $SOURCES',
suffix = '.foo',
src_suffix = '.input',
emitter = modify_targets)
env = Environment(BUILDERS = {'Foo' : bld})
env.Foo('file')
</sconstruct>
<para>
And would yield the following output:
</para>
<scons_output example="builderswriting_ex7" suffix="1">
<scons_output_command>scons -Q</scons_output_command>
</scons_output>
<para>
One very flexible thing that you can do is
use a construction variable to specify
different emitter functions for different
construction variable.
To do this, specify a string
containing a construction variable
expansion as the emitter when you call
the &Builder; function,
and set that construction variable to
the desired emitter function
in different construction environments:
</para>
<scons_example name="builderswriting_MY_EMITTER">
<file name="SConstruct" printme="1">
bld = Builder(action = 'my_command $SOURCES > $TARGET',
suffix = '.foo',
src_suffix = '.input',
emitter = '$MY_EMITTER')
def modify1(target, source, env):
return target, source + ['modify1.in']
def modify2(target, source, env):
return target, source + ['modify2.in']
env1 = Environment(BUILDERS = {'Foo' : bld},
MY_EMITTER = modify1)
env2 = Environment(BUILDERS = {'Foo' : bld},
MY_EMITTER = modify2)
env1.Foo('file1')
env2.Foo('file2')
import os
env1['ENV']['PATH'] = env2['ENV']['PATH'] + os.pathsep + os.getcwd()
env2['ENV']['PATH'] = env2['ENV']['PATH'] + os.pathsep + os.getcwd()
</file>
<file name="file1.input">
file1.input
</file>
<file name="file2.input">
file2.input
</file>
<file name="modify1.in">
modify1.input
</file>
<file name="modify2.in">
modify2.input
</file>
<file name="my_command" chmod="0755">
cat
</file>
</scons_example>
<sconstruct>
bld = Builder(action = 'my_command $SOURCES > $TARGET',
suffix = '.foo',
src_suffix = '.input',
emitter = '$MY_EMITTER')
def modify1(target, source, env):
return target, source + ['modify1.in']
def modify2(target, source, env):
return target, source + ['modify2.in']
env1 = Environment(BUILDERS = {'Foo' : bld},
MY_EMITTER = modify1)
env2 = Environment(BUILDERS = {'Foo' : bld},
MY_EMITTER = modify2)
env1.Foo('file1')
env2.Foo('file2')
</sconstruct>
<para>
In this example, the <filename>modify1.in</filename>
and <filename>modify2.in</filename> files
get added to the source lists
of the different commands:
</para>
<scons_output example="builderswriting_MY_EMITTER" suffix="1">
<scons_output_command>scons -Q</scons_output_command>
</scons_output>
</section>
<!--
<section>
<title>target_factor=, source_factory=</title>
</section>
<section>
<title>target_scanner=, source_scanner=</title>
</section>
<section>
<title>multi=</title>
</section>
<section>
<title>single_source=</title>
</section>
<section>
<title>src_builder=</title>
</section>
<section>
<title>ensure_suffix=</title>
</section>
-->
<section>
<title>Where To Put Your Custom Builders and Tools</title>
<para>
The <filename>site_scons</filename> directories give you a place to
put Python modules and packages that you can import into your &SConscript; files
(<filename>site_scons</filename>),
add-on tools that can integrate into &SCons;
(<filename>site_scons/site_tools</filename>),
and a <filename>site_scons/site_init.py</filename> file that
gets read before any &SConstruct; or &SConscript; file,
allowing you to change &SCons;'s default behavior.
</para>
<para>
Each system type (Windows, Mac, Linux, etc.) searches a canonical
set of directories for site_scons; see the man page for details.
The top-level SConstruct's site_scons dir is always searched last,
and its dir is placed first in the tool path so it overrides all
others.
</para>
<para>
If you get a tool from somewhere (the &SCons; wiki or a third party,
for instance) and you'd like to use it in your project, a
<filename>site_scons</filename> dir is the simplest place to put it.
Tools come in two flavors; either a Python function that operates on
an &Environment; or a Python module or package containing two functions,
<function>exists()</function> and <function>generate()</function>.
</para>
<para>
A single-function Tool can just be included in your
<filename>site_scons/site_init.py</filename> file where it will be
parsed and made available for use. For instance, you could have a
<filename>site_scons/site_init.py</filename> file like this:
</para>
<scons_example name="builderswriting_site1">
<file name="site_scons/site_init.py" printme="1">
def TOOL_ADD_HEADER(env):
"""A Tool to add a header from $HEADER to the source file"""
add_header = Builder(action=['echo "$HEADER" > $TARGET',
'cat $SOURCE >> $TARGET'])
env.Append(BUILDERS = {'AddHeader' : add_header})
env['HEADER'] = '' # set default value
</file>
<file name="SConstruct">
env=Environment(tools=['default', TOOL_ADD_HEADER], HEADER="=====")
env.AddHeader('tgt', 'src')
</file>
<file name="src">
hi there
</file>
</scons_example>
<para>
and a &SConstruct; like this:
</para>
<sconstruct>
# Use TOOL_ADD_HEADER from site_scons/site_init.py
env=Environment(tools=['default', TOOL_ADD_HEADER], HEADER="=====")
env.AddHeader('tgt', 'src')
</sconstruct>
<para>
The <function>TOOL_ADD_HEADER</function> tool method will be
called to add the <function>AddHeader</function> tool to the
environment.
</para>
<!--
<scons_output example="builderswriting_site1" os="posix" suffix="1">
<scons_output_command>scons -Q</scons_output_command>
</scons_output>
-->
<para>
A more full-fledged tool with
<function>exists()</function> and <function>generate()</function>
methods can be installed either as a module in the file
<filename>site_scons/site_tools/toolname.py</filename> or as a
package in the
directory <filename>site_scons/site_tools/toolname</filename>. In
the case of using a package, the <function>exists()</function>
and <function>generate()</function> are in the
file <filename>site_scons/site_tools/toolname/__init__.py</filename>.
(In all the above case <filename>toolname</filename> is replaced
by the name of the tool.)
Since <filename>site_scons/site_tools</filename> is automatically
added to the head of the tool search path, any tool found there
will be available to all environments. Furthermore, a tool found
there will override a built-in tool of the same name, so if you
need to change the behavior of a built-in
tool, <filename>site_scons</filename> gives you the hook you need.
</para>
<para>
Many people have a library of utility Python functions they'd like
to include in &SConscript;s; just put that module in
<filename>site_scons/my_utils.py</filename> or any valid Python module name of your
choice. For instance you can do something like this in
<filename>site_scons/my_utils.py</filename> to add
<function>build_id</function> and <function>MakeWorkDir</function>
functions:
</para>
<scons_example name="builderswriting_site2">
<file name="site_scons/my_utils.py" printme="1">
from SCons.Script import * # for Execute and Mkdir
def build_id():
"""Return a build ID (stub version)"""
return "100"
def MakeWorkDir(workdir):
"""Create the specified dir immediately"""
Execute(Mkdir(workdir))
</file>
<file name="SConscript">
import my_utils
MakeWorkDir('/tmp/work')
print "build_id=" + my_utils.build_id()
</file>
</scons_example>
<para>
And then in your &SConscript; or any sub-&SConscript; anywhere in
your build, you can import <filename>my_utils</filename> and use it:
</para>
<sconstruct>
import my_utils
print "build_id=" + my_utils.build_id()
my_utils.MakeWorkDir('/tmp/work')
</sconstruct>
<para>
Note that although you can put this library in
<filename>site_scons/site_init.py</filename>,
it is no better there than <filename>site_scons/my_utils.py</filename>
since you still have to import that module into your &SConscript;.
Also note that in order to refer to objects in the SCons namespace
such as &Environment; or &Mkdir; or &Execute; in any file other
than a &SConstruct; or &SConscript; you always need to do
</para>
<sconstruct>
from SCons.Script import *
</sconstruct>
<para>
This is true in modules in <filename>site_scons</filename> such as
<filename>site_scons/site_init.py</filename> as well.
</para>
<para>
You can use any of the user- or machine-wide site dirs such as
<filename>~/.scons/site_scons</filename> instead of
<filename>./site_scons</filename>, or use the
<literal>--site-dir</literal> option to point to your own dir.
<filename>site_init.py</filename> and
<filename>site_tools</filename> will be located under that dir.
To avoid using a <filename>site_scons</filename> dir at all,
even if it exists, use the <literal>--no-site-dir</literal>
option.
</para>
</section>
<!--
<section>
<title>Builders That Use Other Builders</title>
<para>
XXX para
</para>
<scons_example name="builderswriting_ex8">
<file name="SConstruct" printme="1">
env = Environment()
#env.SourceCode('.', env.BitKeeper('my_command'))
env.Program('hello.c')
</file>
<file name="hello.c">
hello.c
</file>
</scons_example>
<scons_output example="builderswriting_ex8" suffix="1">
<scons_output_command>scons -Q</scons_output_command>
</scons_output>
</section>
-->
</chapter>
|