ArcPy if part of string not in field, then delete row

Question

I am able to use UpdateCursor to find and delete rows if a field contains part of a string (code below works). Now I want to do the opposite--if part of this string is not in my field, I want to delete the row. Is there a "not_in" function/syntax?

with arcpy.da.UpdateCursor(mySHP, ['OID@', 'Comments']) as cursor:
 for row in cursor:
 if 'this phrase' in row[1]:
 cursor.deleteRow()

Answer 1

Either add a not to the if statement:

with arcpy.da.UpdateCursor(mySHP, ['OID@', 'Comments']) as cursor:
 for row in cursor:
 if 'this phrase' not in row[1]:
 cursor.deleteRow()

or you could add an else block:

with arcpy.da.UpdateCursor(mySHP, ['OID@', 'Comments']) as cursor:
 for row in cursor:
 if 'this phrase' in row[1]:
 pass
 else:
 cursor.deleteRow()

Answer 2

You can also use a where clause to limit the rows returned by the cursor. This should be faster since not all rows are read by the cursor.

import arcpy
mySHP = r'C:\shapefile.shp'
commentfield = 'Comments'
sql = """{0} NOT LIKE '%this frase%'""".format(arcpy.AddFieldDelimiters(mySHP,commentfield))
with arcpy.da.UpdateCursor(mySHP, commentfield, sql) as cursor:
 for row in cursor:
 cursor.deleteRow(row)