can not change double to single dash

[oco]

python 2.7.11

def leftrotate(l, n):
    return l[n:] + l[:n]

def rightrotate(l, n):
    return l[-n:] + l[:-n]

def encode(s, k, kk):
    l = [ord(i) for i in s]
    return leftrotate(''.join([chr(i + k) for i in l]), kk)

def decode(s, k, kk):
    l = [ord(i) for i in rightrotate(s.replace("\\\\","\\"), kk)]
    return ''.join([chr(i - k) for i in l])

>>> "\\".replace("\\\\","\\")
'\\'
>>> encode("xxxxxxQ\|2",3,7)
'_\x7f5{{{{{{T'
>>>
>>> decode("_\x7f5{{{{{{T",3,7)
'xxxxxxQ\\|2'

decode error,

then i try to patch with

decode("_\x7f5{{{{{{T",3,7).replace("\\\\","\\")

but can not change double to single

>>> "\\".replace("\\\\","\\")
'\\'