Alter validation in ArcGIS script tool

Question

I have a script tool in ArcGIS 10.1. Some of the parameters are optional and if they are left blank, will not be processed. They are numerical parameters and I want to enforce this in the tool, so an error is raised if entering any letters in the parameter for example. I have achieved this in updateMessages() setErrorMessage(...) and I get the correct error raised (see graphic)

Validation code is as follows:

 @staticmethod
 def is_string(s):
 try:
   float(s)
   return False
 except ValueError:
   return True
 except TypeError:
   return True

def updateParameters(self):
"""Modify the values and properties of parameters before internal
validation is performed.  This method is called whenever a parameter
has been changed."""
return

def updateMessages(self):
"""Modify the messages created by internal validation for each tool
parameter.  This method is called after internal validation."""

self.params[1].clearMessage()

string_error = 'Please input a number, not text'
if ToolValidator.is_string(self.params[1].value):
  self.params[1].setErrorMessage(string_error)
if ToolValidator.is_string(self.params[2].value):
  self.params[2].setErrorMessage(string_error)
if ToolValidator.is_string(self.params[4].value):
  self.params[4].setErrorMessage(string_error)
if ToolValidator.is_string(self.params[5].value):
  self.params[5].setErrorMessage(string_error)

return

However, the "internal" ArcGIS validation seems to clear the field. If the tool is run the same error message will come up. However since I want to be able to have a blank field, this is not optimal as there is now no way of entering a blank value because the error keeps coming up. Is there any way of preventing ArcGIS validation from blanking out the field so that it retains the original value entered, which is more intuitive?

Also, I thought error messages were supposed to be red, not green - documentation for setErrorMessage() here.

Answer 1

If you set your parameter type to Double, any invalid entry is automatically converted to a 0 by the built-in validation. If you set it to Long, invalid entries are blanked out. Not sure why there is a difference in behavior, but if you can take advantage of it, it may be easier than trying to implement custom validation.

Answer 2

The green dot you're seeing says that's a required parameter and you haven't entered a value for it.

As for your question. I understand you want to validate a parameter to make sure that there is a NUMBER, not TEXT inside. This code below, based off yours does just that. Enter text, get an error. Enter a number, it passes. I hope this is what you're after.

  def updateMessages(self):
"""Modify the messages created by internal validation for each tool
parameter.  This method is called after internal validation."""

def is_string(s):
  try:
    float(s)
    return False
  except ValueError:
    return True
  except TypeError:
    return True    

self.params[0].clearMessage()
string_error = 'Please input a number, not text'

if self.params[0].value or self.params[0].altered:
  if is_string(self.params[0].value):
    self.params[0].setErrorMessage(string_error)   

return

Remember that the parameters are 0-indexed.