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bitbake: user-manual-metadata: Rework section about shell/python functions

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(Bitbake rev: c2bcb5364ff7c702bc1ec2726169f608b445f979)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
This commit is contained in:
Richard Purdie
2014-01-18 14:26:07 +00:00
parent 908fdb5cbc
commit 8705fe2383
1 changed files with 49 additions and 12 deletions
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61
bitbake/doc/user-manual/user-manual-metadata.xml
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@@ -409,22 +409,59 @@
</note>
</section>
<section>
<title>Defining executable metadata</title>
<para><emphasis>NOTE:</emphasis> This is only supported in .bb and .bbclass files.
<section id='functions'>
<title>Functions</title>
<note>
This is only supported in <filename>.bb</filename>
and <filename>.bbclass</filename> files.
</note>
<para>
As with most languages, functions are the building blocks
that define operations.
Bitbake supports shell and Python functions.
An example shell function definition is:
<literallayout class='monospaced'>
do_mytask () {
echo "Hello, world!"
}
some_function () {
echo "Hello World"
}
</literallayout>
This is essentially identical to setting a variable, except that this variable happens to be executable shell code.
An example Python function definition is:
<literallayout class='monospaced'>
python do_printdate () {
import time
print time.strftime('%Y%m%d', time.gmtime())
}
python some_python_function () {
d.setVar("TEXT", "Hello World")
print d.getVar("TEXT", True)
}
</literallayout>
This is the similar to the previous, but flags it as Python so that BitBake knows it is Python code.
In python functions, the "bb" and "os" modules are already
imported, there is no need to import those modules.
The datastore, "d" is also a global variable and always
available to these functions automatically.
</para>
<para>
Bitbake will execute functions of this form using
the <filename>bb.build.exec_func()</filename>, which can also be
called from Python functions to execute other functions,
either shell or Python based.
Shell functions can only execute other shell functions.
</para>
<para>
There is also a second way to declare python functions with
parameters which takes the form:
<literallayout class='monospaced'>
def some_python_function(arg1, arg2):
print arg1 + " " + arg2
</literallayout>
The difference is that the second form takes parameters,
the datastore is not available automatically
and must be passed as a parameter and these functions are
not called with the <filename>exec_func()</filename> but are
executed with direct Python function calls.
The "bb" and "os" modules are still automatically available
and there is no need to import them.
</para>
</section>