String replacing with another string with occurrence count

s='brown box red pencil brown pen red pen red box'
print (s)
s1=s.replace('red','brown')
print (s1)

s='brown box red pencil brown pen red pen red box'
print (s)
s1=s.replace('brown','red',1)
print (s1)

s='brown box red pencil brown pen red pen red box'
print (s)
s1=s.replace('brown','red',2)
print (s1)

s='brown box red pencil brown pen red pen red box'
print (s)
s1=s.replace('brown','red',3)
print (s1)

Searching the pattern in a String using find and index

try:
    s="brown box red pencil brown pen red pen red box"
    print s.find("red")
    print s.find("red",13,len(s))
    print s.find("red",34,len(s))
    print s.find("crow")
    print s.index("red")
    print s.index("red",13,len(s))
    print s.index("red",34,len(s))
    print s.index("crow")
except ValueError:
   print "crow not a pattern in string"