case do problem

[Tracubik]

hi, i've to convert from Pascal this code:

iterations=0;
count=0;
REPEAT;
  iterations = iterations+1;
  ...
  IF (genericCondition) THEN count=count+1;
  ...
  CASE count OF:
	1: m = 1
        2: m = 10
        3: m = 100
UNTIL count = 4 OR iterations = 20

i do something like this:

iterations = 0
count = 0

m_Switch = (1,10,100)

while True:
	iterations +=1
	...
	if (genericCondition):
		count +=1
	...
	try:
		m = m_Switch[count-1]
	except: pass
	if count = 4 or iterations = 20

the problem is that when count = 4 m_Switch[4-1] have no value, so i use 
the try..except.

Is there a better solution to solve this problem? and, generally 
speaking, the try..except block slow down the execution of the program or 
not?

Thank you in advance
Nico