uncompressed_to_compressed.py

import hashlib

b58ab = "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz"

def b58csum(s):
    return hashlib.sha256(hashlib.sha256(s).digest()).digest()[0:4]
    
def b58decode(s, checksum=True):
    idx = 0
    while s[idx] == "1":
        idx += 1
        
    n = 0
    for c in s[idx:]:
        n = n * 58 + b58ab.index(c)
        
    res = long2byte(n)
    res = idx * "\x00" + res
    
    if checksum:
        res, cs = res[:-4], res[-4:]
        assert cs == b58csum(res), "base58 checksum failed"
        
    return res

def b58encode(s, checksum=True):
    if checksum:
        s += b58csum(s)
        
    idx = 0
    while s[idx] == "\x00":
        idx += 1
        
    n = byte2long(s)
    res = ""
    while n > 0:
        res = b58ab[n % 58] + res
        n /= 58
        
    return "1" * idx + res

def byte2long(s):
    res = 0
    for c in s:
        res = (res << 8) | ord(c)
    return res

def long2byte(n, sz=None):
    res = ""
    while n > 0:
        res = chr(n & 0xff) + res
        n >>= 8
        
    if sz is not None:
        res = res.rjust(sz, "\x00")
        
    return res


uncompressed = "5KYZdUEo39z3FPrtuX2QbbwGnNP5zTd7yyr2SC1j299sBCnWjss"

key = b58decode(uncompressed) # also removes checksum bytes
key += "\x01"
compressed = b58encode(key) # adds checksum

assert compressed == "L4rK1yDtCWekvXuE6oXD9jCYfFNV2cWRpVuPLBcCU2z8TrisoyY1"

print compressed