Koan at 13:52, 15 May 2019

2019-05-15T13:52:54Z

← Older revision		Revision as of 13:52, 15 May 2019
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	override the setting of the ?=. Any following ?= and ??= will not change		override the setting of the ?=. Any following ?= and ??= will not change
	the setting.		the setting.


	----		----

Koan: /* Python assignment operators */

2019-05-15T13:52:33Z

Python assignment operators

← Older revision		Revision as of 13:52, 15 May 2019
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	variable, the last one will be used.		variable, the last one will be used.

			A ?= following a ??= will set the variable. Only a = will be
			override the setting of the ?=. Any following ?= and ??= will not change
			the setting.

	----		----

Koan: /* Python assignment operators */

2019-05-15T13:51:19Z

Python assignment operators

← Older revision		Revision as of 13:51, 15 May 2019
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	----		----
	-

	* Early Default Value Assignment (?=)		* Early Default Value Assignment (?=)

Koan: /* Python assignment operators */

2019-05-15T13:51:05Z

Python assignment operators

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Koan: Created page with "== Python assignment operators == - Variable Setting (=) Set a variable by assigning it a value using the = sign. Values must be surrounded by double quotes. * VAR = "..."

2019-05-15T13:41:51Z

Created page with "== Python assignment operators == - *Variable Setting (=)* Set a variable by assigning it a value using the *=* sign. Values must be surrounded by double quotes. * VAR = "..."

New page

== Python assignment operators ==

-

*Variable Setting (=)*

Set a variable by assigning it a value using the *=* sign. Values must
be surrounded by double quotes.

*
VAR = "value"
*

In this example, *VAR* is set to *value*.
-

*Early Default Value Assignment (?=)*

A variable can be early-assigned a default value using the *?=* assignment
operator:

*
A ?= "1"
B ?= "2"
B ?= "3"
*

In this example *A* will contain *1* if it was not previously set. *B* will
contain *2* because the *?=* assignment operator is immediate meaning
that if there are multiple *?=* assignments to a single variable, the
first one will be used.
-

*Late Default Value Assignment (??=)*

A variable can be late-assigned a default value using the *??=* assignment
operator:

*
A ??= "1"
B ??= "2"
B ??= "3"
*

In this example *A* will contain *1* if it was not previously set. *B* will
contain *3* because the *??=* assignment operator is a late or lazy
assignment operator and assignment will not take place until the end of the
parsing process. If there are multiple *??=* assignments to a single
variable, the last one will be used.
-

*Variable Expansion*

Bitbake supports referencing a variables content similar to shell
scripting.

*
A = "jumps over"
B = "The quick brown fox ${A} the lazy dog."
echo $B
*

This results in the the text *The quick brown fox jumps over the lazy
dog.* printed to the console.
-

*Immediate Variable Expansion (:=)*

Typically, Bitbake expands a variable when it is used. The *:=* assignment
operator however expands the variable immediately when it is assigned.

*
A = "11"
B = "B:${A}"
A = "22"
C := "C:${A}"
echo $C $B
*

This results in *C:22 B:22* printed to the console since the content of *
A* is expanded immediately on assignment to variable *C*. Variable *B* did
not get expanded until it was actually used in the *echo*statement.
-

*Appending (+=) and Prepending (=+)*

The *+=* and *=+* append and prepend variables respectively while adding
a single space between the values.

*
A = "12"
A += "34"
B = "89"
B =+ "67"
*

This results in variable *A* containing *12 34* and variable *B*
containing *67 89*.
-

*Appending (.=) and Prepending (=.) without Spaces*

The *.=* and *=.* work like the above appending and prepending operators
however without placing an additional space between the values.

*
A = "12"
A .= "34"
B = "89"
B =. "67"
*

This results in variable *A* containing *1234* and variable *B*
containing *6789*.

Python assignment operators - Revision history

Koan at 13:52, 15 May 2019

Koan: /* Python assignment operators */

Koan: /* Python assignment operators */

Koan: /* Python assignment operators */

Koan: Created page with "== Python assignment operators == - *Variable Setting (=)* Set a variable by assigning it a value using the *=* sign. Values must be surrounded by double quotes. * VAR = "..."

Koan: Created page with "== Python assignment operators == - Variable Setting (=) Set a variable by assigning it a value using the = sign. Values must be surrounded by double quotes. * VAR = "..."