How To: Create sequential numbers in a field using Python in the Field Calculator

GIS

1 Create a new short integer field.

2 Right-click the new field and select Field Calculator.

3 Set the Parser to Python.

4 Check the check box for Show Codeblock.

5 Paste the following into the Pre-Logic Script Code:

rec=0
def autoIncrement():
 global rec
 pStart = 1
 pInterval = 1
 if (rec == 0):
  rec = pStart
 else:
  rec += pInterval
 return rec

6 Paste the following code in the smaller box below the Pre-Logic Script Code:

autoIncrement()

7 Click OK.

Source: [Source 1]