ArcGIS Pro Tutorial: Create Attractive Label Expression Using Python in ArcGIS Pro

Why Use Python for Label Expressions?

Python label expressions in ArcGIS Pro offer several advantages:

• Dynamic Content: Display calculated values based on attribute data
• Conditional Formatting: Apply different styles based on attribute conditions
• Data Manipulation: Format numbers, dates, and text for better readability
• Advanced Logic: Create complex labeling rules with multiple conditions

Getting Started with Python Label Expressions

Step 1: Enable Labeling

First, ensure your layer has labeling enabled:

1. Right-click on your layer in the Contents pane
2. Select Labeling → Label Features
3. Or go to the Labeling tab and click Label

Step 2: Access Label Expression Editor

1. Select your layer in the Contents pane
2. Go to the Labeling tab
3. Click on Label Class → Expression
4. In the Label Expression dialog, change the Parser to Python
5. Check the Advanced checkbox to enable full Python scripting

Basic Python Label Expression Examples

Example 1: Simple Field Concatenation

def FindLabel([NAME], [POPULATION]):
    return [NAME] + " (" + str([POPULATION]) + ")"

This expression combines the NAME field with population data in parentheses.

Example 2: Conditional Formatting

def FindLabel([POPULATION]):
    pop = [POPULATION]
    if pop >= 1000000:
        return "<CLR red='255'>" + "{:,}".format(pop) + "</CLR>"
    elif pop >= 100000:
        return "<CLR red='0' green='0' blue='255'>" + "{:,}".format(pop) + "</CLR>"
    else:
        return "{:,}".format(pop)

This expression changes the color and format of population labels based on their values.

Advanced Python Label Techniques

Working with Dates

def FindLabel([DATE_ESTABLISHED]):
    import datetime
    date_str = [DATE_ESTABLISHED]
    if date_str:
        try:
            date_obj = datetime.datetime.strptime(date_str, "%Y-%m-%d")
            return date_obj.strftime("%B %d, %Y")
        except:
            return date_str
    return ""

Formatting Numbers and Currency

def FindLabel([REVENUE]):
    revenue = [REVENUE]
    if revenue is not None:
        return "${:,.2f}".format(revenue)
    return "N/A"

Multi-Line Labels with HTML Tags

def FindLabel([NAME], [TYPE], [RATING]):
    name = "<BOL>" + [NAME] + "</BOL>"
    type_info = "<ITA>" + [TYPE] + "</ITA>"
    rating = "Rating: " + str([RATING]) + "/5"
    return name + "\n" + type_info + "\n" + rating

Styling Labels with HTML Tags

ArcGIS Pro supports various HTML tags for label formatting:

Best Practices for Python Label Expressions

• Error Handling: Always include try-except blocks to prevent labeling failures
• Performance: Keep expressions simple to maintain good map performance
• Readability: Use clear variable names and add comments to complex expressions
• Testing: Test expressions with various data scenarios
• Consistency: Maintain consistent formatting across similar label types

Troubleshooting Common Issues

Expression Not Working

Check these common issues:

• Ensure the Parser is set to Python
• Verify field names are correct (case-sensitive)
• Check that the Advanced checkbox is selected
• Look for syntax errors in your Python code

Labels Not Appearing

If your labels aren’t displaying:

• Confirm labeling is enabled for the layer
• Check that label class visibility is turned on
• Verify label scale dependencies
• Ensure there’s sufficient space for label placement