Python in field calculator parsing error

Question

I'm trying to perform a selection in an attribute table based on two columns. The intital step I'm intending to perform is to select fields between values, e.g. (a > 0 and a < 10) and from this selection then in the second step find fields in another column, e.g. (if b == 1, return "OK" elif b == 2, return "NOT OK"). I think I'm safe with the logic behind it, but the Python scripting seems to be my drawback. What Am I doing wrong since I get parsing error everytime I try to execute the code?

def Check ( a, b ):
 for (a > 0) and (a < 10):
  if b == 2:
   return "NO"
  elif b == 1:
   return "YES"
  elif b == 0:
   return "MAYBE" 
 for (a => 10) and (a < 15):
  if b == 2:
   return "NO"
  elif b == 1:
   return "YES"
  elif b == 0:
   return "MAYBE"
 for (a > 15):
  if b == 2:
   return "YES"
  elif b == 1:
   return "NO"
  elif b == 0:
   return "MAYBE"

Result (Check)

Answer 1

Your main problem is the use of "for" instead of "if" with the conditionals related to the first field.

def Check ( a, b ):
 if (a > 0) and (a < 10): #if you don't have negative values, it could be if a<10: . Also, note that you will not return any result for negative values with the present script.
  if b == 2:
   return "NO"
  elif b == 1:
   return "YES"
  elif b == 0:
   return "MAYBE" 
 elif (a => 10) and (a < 15): #elif a<15:
  if b == 2:
   return "NO"
  elif b == 1:
   return "YES"
  elif b == 0:
   return "MAYBE"
 elif (a > 15): #else:
  if b == 2:
   return "YES"
  elif b == 1:
   return "NO"
  elif b == 0:
   return "MAYBE"

Also, make sure that you run it with

Check(!fielda!,!fieldb!)

By the way, in your example the value of "a" doesn't influence the output, so this could be skipped.