# shift characters

def shiftchrs(s, shift):

# Shift characters A-Z and a-z (65-90 and 97-122)

s1 = ''.join([chr(i) for i in range(65,123) if i not in range(91,97)])

s2 = s1[:26][shift:]+s1[:26][:shift]+s1[26:][shift:]+s1[26:][:shift]

m = string.maketrans(s1,s2)

return string.translate(s, m)

shift = -4

s = "Scramble this string."

print shiftchrs(s, shift)

# >>> Wgveqfpi xlmw wxvmrk.

# >>> Oynwixha pdeo opnejc.