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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