Can a user input variable be used in an expression variable string for CalculateField_management ?

MPach

First off, I know there's a better title I could have used so I apologize for the confusion. 

I have a short script I've written that takes a some user entered information parcel data a field the calculation will be done for.  

 

 

 

# Import arcpy module
import arcpy

# Script arguments
Parcels = arcpy.GetParameterAsText(0)

Field2Calc_for = arcpy.GetParameterAsText(1) #field type derived from Parcels

lengthField = arcpy.GetParameterAsText(2)  #field type derived from Parcels

widthField = arcpy.GetParameterAsText(3)  #field type derived from Parcels

num = arcpy.GetParameterAsText(2) #Long Type 

# Local variables

expression = r'reclass' + str((r'!' + + widthField + r'!', r'!' + lengthField + r'!' , num))

codeblock = """ def reclass(lengthField,widthField,num):
                   if ((lengthField/num) >= (widthField)):
                       return 'True'
                   else:
                       return '' """

# Process: Calculate Field
arcpy.CalculateField_management(Parcels, Field2Calc_for, expression, "PYTHON", codeblock)

 

I'm having a difficult time figuring out how to correctly set the string for the expression variable. What I'd like to do is take my user input lengthField & widthField parameters and use variable substitution in the expression variable. I'm having a hard time figuring out if that's possible and what the syntax would look like. The examples for the the CalculateField_management method have the field name hard coded into the script, but I'd like to try to avoid that if possible so the user can choose the field. 

I appreciate any help and I'm pretty sure it's just something dumb that I'm overlooking b/c that's usually the case.

Thanks, 

Mark

MPach

Thanks @RhettZufelt  this worked great. I just need to adjust the expression a bit because num was an int type.

expression = 'reclass(!{0}!,!{1}!,{2})'.format(lengthField, widthField, num)