basic_for_aj.py

import arcpy

# input table and field name to modify
table = r"path\to\your\table"
field = "your_field_name"

# loop through each row and modify the field value
with arcpy.da.UpdateCursor(table, [field]) as cursor:
    for row in cursor:
        # get the original field value
        orig_value = row[0]
        # split the value by commas and keep the first element (city name)
        city_name = orig_value.split(",")[0]
        # set the modified value back in the field
        row[0] = city_name
        cursor.updateRow(row)

# without modifying the existing data.
import arcpy

# Set input table and field names
input_table = r"path/to/your/table"
input_field = "original_field_name"
new_field = "modified_field_name"

# Add new field to hold modified city names
arcpy.AddField_management(input_table, new_field, "TEXT", field_length=50)

# Update new field with modified city names
with arcpy.da.UpdateCursor(input_table, [input_field, new_field]) as cursor:
    for row in cursor:
        # Get city name by splitting original field value
        city = row[0].split(",")[0]
        # Remove any leading or trailing spaces
        city = city.strip()
        # Update new field with modified city name
        row[1] = city
        cursor.updateRow(row)

This code creates a new text field with a length of 50 characters and then uses an update cursor to loop through each row of the input table. For each row, it splits the value in the original field by commas, gets the first value (the city), removes any leading or trailing spaces, and then updates the new field with the modified city name. The original data remains unchanged.