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':
decoded = decode(sys.argv[2])
sys.stdout.buffer.write(decoded)
else:
help_n_exit()
