import re

data = """***   DATA
     1    253.31     78.20     490.0         0 0 1 0 0
   101         0         0         0         0         0         0          
     1         2         3         4         5         6
     .
     .
     .
     .
    10         A         B         C         0 0 1 0 0
   110         0         0         0         0         0         0          
    20        21        22        23        24        25"""
mldata = data.split('\n')

regex = re.compile(r'\b([A-Za-z])\b')
replacement = "test"

for line in mldata:
	newline = re.sub(regex,replacement,line)
	print newline