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Parameter

In this topic

  1. Summary
  2. Discussion
  3. Syntax
  4. Properties
  5. Method Overview
  6. Methods
  7. Code sample
Related topics
  1. Setting script tool parameters
  2. Value
  3. Filter
  4. Schema
  5. Customizing script tool behavior

Summary

Every tool parameter has an associated Parameter object with properties and methods that are useful in tool validation.

Discussion

Although many Parameter object properties are read/write, most of these properties can only be set or modified when you initially create or modify the object. Several properties, including name, displayName, datatype, direction, and parameterType, establish the characteristics of a tool and cannot be modified during validation methods (such as updateMessages and updateParameters).

Syntax

 Parameter  ({name}, {displayName}, {direction}, {datatype}, {parameterType}, {enabled}, {category}, {symbology}, {multiValue})
ParameterExplanationData Type
name

The parameter name.

(The default value is None)

String
displayName

The parameter label as shown on the tool's dialog box.

(The default value is None)

String
direction

The Input/Output direction of the parameter.

(The default value is None)

String
datatype

The data type of the parameter.

For a list of parameter data types, see Geoprocessing data types.

(The default value is None)

String
parameterType

parameterType can be Required, Optional, or Derived. Derived means that the user of your tool does not enter a value for the parameter. Derived types are always output parameters.

(The default value is None)

String
enabled

False if the parameter is unavailable.

(The default value is None)

Boolean
category

The category of the parameter.

(The default value is None)

String
symbology

The path to a layer file (.lyr or .lyrx) used for drawing the output.

(The default value is None)

String
multiValue

True if the parameter is a multivalue parameter.

(The default value is None)

Boolean

Properties

PropertyExplanationData Type
altered
(Read Only)

True if the user has modified the value.

Boolean
category
(Read and Write)

The category of the parameter.

String
columns
(Read and Write)

The column data types and names of a value table parameter are set using a list of lists.

import arcpy
param = arcpy.Parameter()
param.datatype = "GPValueTable"
param.columns = [["GPFeatureLayer", "Features"], ["GPLong", "Ranks"]]
String
datatype
(Read and Write)

The data type of the parameter.

For a list of parameter data types, see Geoprocessing data types.

String
defaultEnvironmentName
(Read and Write)

The geoprocessing environment setting used to set the parameter's default value.

String
direction
(Read and Write)

The Input/Output direction of the parameter.

String
displayName
(Read and Write)

The parameter label as shown on the tool's dialog box.

String
displayOrder
(Read and Write)

The order in which a parameter is displayed on the tool's dialog box. This may be different from the order the parameters are accessed from Python.

Integer
enabled
(Read and Write)

False if the parameter is unavailable.

Boolean
filter
(Read Only)

The filter to apply to values in the parameter.

Filter
filters
(Read and Write)

Similar to filter but used to support value table parameters.

class SampleTool(object):
    # __init__ left out to simplify example

    def getParameterInfo(self):
        in_fc = arcpy.Parameter(
            name='in_features',
            displayName='Input Features',
            datatype='GPFeatureLayer',
            direction='Input',
            parameterType='Required')

        vt = arcpy.Parameter(
            name = 'summary_fields',
            displayName = 'Summary fields',
            datatype = 'GPValueTable',
            direction = 'Input',
            parameterType = 'Optional')

        vt.parameterDependencies = [in_fc.name]
        vt.columns = [['Field', 'Field'], ['GPString', 'Statistic'], ['GPDouble', 'Multiplier']]
        vt.filters[0].list = ['Double', 'Float', 'Short', 'Long']
        vt.filters[1].type = 'ValueList'
        vt.filters[1].list = ['SUM', 'MIN', 'MAX', 'MEAN']
        vt.filters[2].type = 'Range'
        vt.filters[2].list = [0,10]
Filter
hasBeenValidated
(Read Only)

True if the internal validation routine has checked the parameter.

Boolean
message
(Read Only)

The message to be displayed to the user.

String
multiValue
(Read and Write)

True if the parameter is a multivalue parameter.

Boolean
name
(Read and Write)

The parameter name.

String
parameterDependencies
(Read and Write)

A list of indexes of each dependent parameter.

In a script tool, parameterDependencies is set with a list of parameter indexes; in a Python toolbox tool, parameterDependencies is set with a list of parameter names.

Integer
parameterType
(Read and Write)

parameterType can be Required, Optional, or Derived. Derived means that the user of your tool does not enter a value for the parameter. Derived types are always output parameters.

  • Required —A Required parameter requires an input value from the user. The tool cannot be executed until a value has been supplied.
  • Optional — An Optional parameter does not require a value.
  • Derived —A Derived parameter is only for output parameters. A derived output parameter does not show on the tool dialog box.
String
schema
(Read Only)

The schema of the output dataset.

Schema
symbology
(Read and Write)

The path to a layer file (.lyr or .lyrx) used for drawing the output.

String
value
(Read and Write)

The value of the parameter.

Object
valueAsText
(Read Only)

The value of the parameter as a string.

Note:

For Python toolboxes only.

String
values
(Read and Write)

The values of the Value Table parameter, which is set using a list of lists.

Variant

Method Overview

MethodExplanation
clearMessage ()

Clears out any message text and sets the status to informative (no error or warning).

hasError ()

Returns True if the parameter contains an error.

To evaluate whether a parameter has an error, hasError should be called within the tool validation's updateMessages method.

hasWarning ()

Returns True if the parameter contains a warning.

isInputValueDerived ()

Returns True if the tool is being validated inside a Model and the input value is the output of another tool in the model.

setErrorMessage (message)

Sets a parameter as having an error with the supplied message. Tools do not execute if any of the parameters have an error.

setIDMessage (message_type, message_ID, {add_argument1}, {add_argument2})

Sets a parameter as having a system message.

setWarningMessage (message)

Sets a parameter as having an error with the supplied message. Unlike errors, tools will execute with warning messages.

Methods

clearMessage ()
hasError ()
Return Value
Data TypeExplanation
Boolean

True if the parameter contains an error.

hasWarning ()
Return Value
Data TypeExplanation
Boolean

True if the parameter contains a warning. 

isInputValueDerived ()
Return Value
Data TypeExplanation
Boolean

True if the tool is being validated inside a Model and the input value is the output of another tool in the model. 

setErrorMessage (message)
ParameterExplanationData Type
message

The string to be added as an error message to the geoprocessing tool messages.

String
setIDMessage (message_type, message_ID, {add_argument1}, {add_argument2})
ParameterExplanationData Type
message_type

Defines whether the message will be an error or a warning.

  • ERROR —The message will be an error message.
  • WARNING —The message will be a warning message.
String
message_ID

The message ID allows you to reference existing system messages.

Integer
add_argument1

Depending on which message ID is used, an argument may be necessary to complete the message. Common examples include dataset or field names. The data type is variable depending on the message.

Object
add_argument2

Depending on which message ID is used, an argument may be necessary to complete the message. Common examples include dataset or field names. The data type is variable depending on the message.

Object
setWarningMessage (message)
ParameterExplanationData Type
message

The string to be added as a warning message to the geoprocessing tool messages.

String

Code sample

Parameter example

Enabling or disabling a parameter in a ToolValidator class.

def updateParameters(self):
    # If the option to use a weights file ("Get Spatial Weights From File") 
    # is selected, enable the parameter for specifying the file; 
    # otherwise, disable it

    if self.params[3].value == "Get Spatial Weights From File":
        self.params[8].enabled = True
    else:
        self.params[8].enabled = False

    return
Parameter example 2

Setting a default value for a parameter in a ToolValidator class.

def updateParameters(self):
    # Set the default distance threshold to 1/100 of the larger of
    # the width or height of the extent of the input features.  Do
    # not set if there is no input dataset yet, or the user has set
    # a specific distance (Altered is true).

    if self.params[0].value:
        if not self.params[6].altered:
            extent = arcpy.Describe(self.params[0].value)
        width = extent.XMax - extent.XMin
        height = extent.YMax - extent.YMin

        if width < height:
            self.params[6].value = width / 100
        else:
            self.params[6].value = height / 100

        return
Parameter example 3

Setting a custom error message for a parameter in a ToolValidator class.

def updateMessages(self):
    self.params[6].clearMessage()

    # Check to see if the threshold distance contains a value of
    # zero and the user has specified a fixed distance band.
    if self.params[6].value <= 0:
        if self.params[3].value == "Fixed Distance Band":
            self.params[6].setErrorMessage(
                "Zero or a negative distance is invalid when "
                "using a fixed distance band. Please use a "
                "positive value greater than zero.")
        elif self.params[6].value < 0:
            self.params[6].setErrorMessage(
                "A positive distance value is required when "
                "using a fixed distance band. Please specify "
                "a distance.")

    return

Related topics

  • Setting script tool parameters
  • Value
  • Filter
  • Schema
  • Customizing script tool behavior

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In this topic
  1. Summary
  2. Discussion
  3. Syntax
  4. Properties
  5. Method Overview
  6. Methods
  7. Code sample
Related topics
  1. Setting script tool parameters
  2. Value
  3. Filter
  4. Schema
  5. Customizing script tool behavior