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#author("2026-07-01T14:11:27+09:00;2023-02-23T23:33:35+09:00","default:vip","vip")
#author("2026-07-01T14:15:47+09:00;2023-02-23T23:33:35+09:00","default:vip","vip")
[[練習問題]]
 #!/usr/bin/python
 import sys
 from string import ascii_lowercase, ascii_uppercase, digits
 
 table = ascii_uppercase + ascii_lowercase + digits + '+/'
 
 def encode(filename):
     with open(filename, 'rb') as f:
         return _e(f.read())
     
 def decode(filename):
     with open(filename, 'r') as f:
         return _d(f.read())
 
 def _e(byte_arr):
     bit = ''.join(f"{b:08b}" for b in byte_arr)
     n_extra = -len(bit)%6
     bit += '0' * n_extra
     res = ''.join(table[int(bit[i:i+6], 2)] for i in range(0, len(bit), 6))
     return res + '=' * (-len(res) % 4)
 
 def _d(b64str):
     bit = ''.join(f"{table.find(c):06b}" for c in b64str if c in table)
     n_extra = len(bit)%8
     bit = bit[0:len(bit)-n_extra]
     res = bytes(int(bit[i:i+8], 2) for i in range(0, len(bit), 8))
     return res
 
 def help_n_exit():
     print(f"""\
 usage: python my_base64.py option filename
 
 option:
   -e : encode binary file to Base64 string
   -d : decode Base64 file to binary string
 
 example:
   encode: b'VIP de programming' -> {_e(b"VIP de programming")}
   decode: VklQIGRlIHByb2dyYW1taW5n -> {_d("VklQIGRlIHByb2dyYW1taW5n")}\
 """)
     exit()
     
 if len(sys.argv) < 3:
     help_n_exit()
     
 option = sys.argv[1]
 if option == '-e':
     encoded = encode(sys.argv[2])
     W = 76
     res = '\n'.join(encoded[i:i+W] for i in range(0, len(encoded), W))
     print(res)
 elif option == '-d':
     print(f"decoding {sys.argv[2]} ...")
     res = decode(sys.argv[2])
     sys.stdout.buffer.write(res)
     decoded = decode(sys.argv[2])
     sys.stdout.buffer.write(decoded)
 else:
     help_n_exit()