PYSON#
PYSON is the PYthon Statement and Object Notation. It is a lightweight domain specific language for the general representation of statements. PYSON is used to encode statements which can be evaluated in different programming languages, serving for the communication between trytond and any third party software. A PYSON parser can easily be implemented in other programming languages. So third party softwares do not need to depend on Python to be able to fully communicate with the Tryton server.
PYSON is a deterministic algorithm which will always succeed to evaluate statements. There is a default behavior for unknown values. It is statically typed and checked on instantiation.
There is also a reference documentation of the API.
Syntax#
The syntax of a PYSON statement follows this pattern:
Statement(argument1[, argument2[, ...]])
where arguments can be another statement or a value. The evaluation direction is inside out, deepest first.
PYSON Examples#
Given the PYSON statement:
Eval('active_id', -1)
Eval
checks the evaluation context for the variable
active_id
and returns its value or -1
if not defined.
A similar expression in Python looks like this:
'active_id' in locals() and active_id or -1
Given the PYSON statement:
Not(Bool(Eval('active')))
Eval
checks the evaluation context for a variable active
and
returns its value to Bool
or ''
if not defined.
Bool
returns the corresponding boolean value of the
former result to Not
.
Not
returns the boolean negation of the previous
result.
A similar expression in Python looks like this:
'active' in locals() and active == False
Given the PYSON statement:
Or(Not(Equal(Eval('state'), 'draft')), Bool(Eval('lines')))
In this example are the results of two partial expressions
Not(Equal(Eval('state'), 'draft'))
and Bool(Eval('lines'))
evaluated by a logical OR operator. The first expression part is
evaluated as follow: When the value of Eval('state')
is equal to
the string 'draft'
then return true, else false.
Not
negates the former result.
A similar expression in Python looks like this:
'states' in locals() and 'lines' in locals() and state != 'draft' or bool(lines)
Given the PYSON statement:
If(In('company', Eval('context', {})), '=', '!=')
In this example the result is determined by an if-then-else condition.
In('company', Eval('context', {}))
is evaluated like this: When
the key 'company'
is in the dictionary context
, returns
true, otherwise false.
If
evaluates the former result and returns the string
'='
if the result is true, otherwise returns the string '!='
.
A similar expression in Python looks like this:
'context' in locals() and isinstance(context, dict) and 'company' in context and '=' or '!='
Given the PYSON statement:
Get(Eval('context', {}), 'company', 0))
Eval
checks the evaluation context for a variable
context
if defined, return the variable context
, otherwise return an
empty dictionary {}
.
Get
checks the former resulting dictionary and returns
the value of the key 'company'
, otherwise it returns the number 0
.
A similar expression in Python looks like this:
'context' in locals() and context.get('company', 0) or 0