[Ironpython-users] PythonAst

[Rutger Koperdraad]

Hi,

 

I'm writing an application in Visual Basic .NET that allows the users to
write scripts in IronPython for some specialized customization needs. Users
provide a script, a number of variable names and values, and an expression.
For example, to customize the displaying of dates, they could provide the
following script, variables and expressions:

 

Script:

dateformat = 'dddd d MMMM yyyy'

prefix = 'Birth date: '

 

def format(d):

  import System

  dd = System.DateTime.Parse(d)

  return dd.ToString(dateformat)

 

Variables:

birthdate = '10/04/1968'

 

Expression:

prefix + format(birthdate)

 

In Visual Basic .NET I create a ScriptRuntime, ScriptEngine, ScriptSource
and ScriptScope. I add the variables to the ScriptScope, execute the script
and evaluate the expression. That's working like a charm.

 

I would like to add functionality that automatically detects which variables
need to be defined. In the above example, I would like the user to specify
the script and the expression and the software to detect that the variable
"birthdate" is needed and prompt for a value. I tried to do so with
PythonAst, but I cannot find sufficient documentation on internet to get it
working in general. The functions below work to some extent. They get all
the names from the expression and then remove "format" for being a function
name and not a variable name. But this function still returns "prefix",
which it shouldn't. Any help or documentation would be appreciated.

 

    Public Function GetVariableNames(ByVal strExpression As String) As
StringCollection

        Try

            If Not String.IsNullOrEmpty(strExpression) Then

 

                ' Create a script runtime if needed

                If m_objScriptRuntime Is Nothing Then

                    m_objScriptRuntime =
ScriptRuntime.CreateFromConfiguration()

                End If

 

                ' Create the objects needed by the expression walker

                Dim objEngine As ScriptEngine =
m_objScriptRuntime.GetEngine(ScriptLanguage)

                Dim objSource As ScriptSource =
objEngine.CreateScriptSourceFromString(strExpression,
SourceCodeKind.Expression)

                Dim objSourceUnit As SourceUnit =
Providers.HostingHelpers.GetSourceUnit(objSource)

                Dim objLanguageContext As LanguageContext =
HostingHelpers.GetLanguageContext(objEngine)

                Dim objCompilerContext As New CompilerContext(objSourceUnit,
objLanguageContext.GetCompilerOptions(), ErrorSink.Default)

                Dim objParser As Parser =
Parser.CreateParser(objCompilerContext, New PythonOptions)

                Dim objPythonAst As PythonAst =
objParser.ParseSingleStatement()

                Dim objExpressionWalker As New ExpressionWalker

 

                ' Determine the variable names

                Call objPythonAst.Walk(objExpressionWalker)

 

                Return objExpressionWalker.VariableNames

            End If

        Catch ex As Exception

            Call LogException(strExpression, ex)

        End Try

 

        Return New StringCollection

    End Function

 

    Private Class ExpressionWalker

        Inherits PythonWalker

 

        Private clnVariableNames As New StringCollection

 

        Public ReadOnly Property VariableNames As StringCollection

            Get

                Return clnVariableNames

            End Get

        End Property

 

        Public Overrides Sub PostWalk(node As NameExpression)

            Call clnVariableNames.Add(node.Name)

 

            Call MyBase.PostWalk(node)

        End Sub

 

        Public Overrides Sub PostWalk(node As CallExpression)

            Dim objNameExpression As NameExpression = TryCast(node.Target,
NameExpression)

 

            If Not objNameExpression Is Nothing Then

                Call clnVariableNames.Remove(objNameExpression.Name)

            End If

 

            Call MyBase.PostWalk(node)

        End Sub

 

    End Class

 

With best regards,

Rutger Koperdraad.

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