UnicodeDecodeError: 'utf8' codec can't decode byte 0xaf in position 3: invalid start byte in python 2.7
Simply put not all bytes and/or byte sequences map to unicode characters. In fact most byte sequences do not have a UTF-8 character mapping.
The common solution is to convert binary to an encoding that can handle all byte values, the most common are Base64 and Hexadecimal.
using windows10 python 2.7
my code for decryption


    def decrypt(self, enc):
            enc = b64decode(enc)
            iv = enc[:16]
            cipher = AES.new(self.key, AES.MODE_CBC, iv)
            print cipher,"======"
            dec = cipher.decrypt(enc[16:])
            #print dec,"========",dec
            unp = unpad(dec)
            print unp,"=========","=fdkjfsdklfsdjndjdjk"
            decode = unp.decode('utf8')
            #decode = unp.decode('utf8')
            print decode
            # unpad(cipher.decrypt(enc[16:])).decode('utf8')
            return decode


while decrypting the encrypted response cipher.decrypt(enc[16:]) line gives me below output. But actually It should be the XML format.

 )^»3(Fm╠¡Oå┤╖¢iOÑ>s▌B¿▌╥≥┐Éj6╬░¢√(å¥  2?J≤ôGOL═\¥°t╬╚ΓÜ▐╝Φ÷═AQw≥[&nΣ±ƒ∩(╩ûGN~[3bgrHPÜ4%╖H⌡▄wÅ|■Çq≥½÷σHñxìdºwë±!│▐íWÇÿΘ╦σ╖è#X▓┤2ÿ       ┘╟ƒΣ°Y░çNßæÅαb3f«─O(Wo9┐A╕t£╧{K [X┴┬ÜHΘ⌠X4┬Æ≡~╠h3ε┘σmÉfú.Fú╜₧c!_╒▐wα²A/╒|─sY%=⌐▒Yö╕[╞ε░::tA┴₧µ≤²∙C─A█₧╕╧τ╙x≤rƒú░uú█å┬-╤`╡f╕^∞tΦ½q╗&╪─╘¥&┐Σ₧▌(╙┌JüñÇäQ¥/*ó▐H!C┬+δà\Bah╘áÆXu╥C█│¼)ë╩╓*E(÷·├à√¿╨╧1Θ·0≈º²║Ås┬xOò}a╪╔╫HÜq┬gqÅÖ⌐4~v╖·9╥Ü$wçZ▌╗┬? /Zj12^}&t$F=SBKhöåε è╝o╪█º8fìîé╫=«·gO:Z╢≡2╔K«Θ uè/╩ {⌐Åwwε^α┼µk4┘Ñ╧:ƒ16║╞ⁿB°¢üdó?eB┼P┌L_90]\5W╥µA⌐
    #Mq╤ìⁿ²ç≥Θ·▓F₧▀) ç@ë╒╖às2╡}πL╕╨60ä┌ù6▒.rn╔jⁿR¢∙µIëÉ╝µè}c≈σß_αäcª/╤"lK*└qX2H öφq#â½æΘjÄ% é6#üY█▓aFßα█÷I║n+⌡▄Ä!jTÄ√∩yr¥d"╛¬z√ⁿµº½êYⁿπ¬2[╕¿≡ÿ │Uv?{τæτ°QÜÄµ╨íkUFπ╚BπÆ! Hiåƒ╒£αì≥Æεtr█[╤àÆ█oíΩ("┤╞åMÜò╝D3╬¿VτΩr▓ÜÆÿ$┌)⌠≡\~╩▀Rr≡y£₧≤║L>╙ ╘µv9ÿæ├@B≡µ£╕Ew╗yÿtXeY.αÑsú Y±£∩=yy¥óüΣÆF╧╦á─}      Oƒ≥-9[≤¢fúΣe3&Öÿ░ìç·ntÄO
    l∙m¥\╞&KêëR»s╔E2╨ª│OV≥░m═╬2┬₧ú(ûöz¢¼╣\≤5nqò+╝±Äm{Gσ╝ROφNµàg╛RV╨;Lδa ,é/ⁿY╜|┤ñ╔÷πvⁿ╞W▓π}Rå#h$*πAò¼2╝CÅk*l"h╕≥aÆhæt)9▐░╝.]B}-╢└∩Iσw┬╚D&5≡▒²`WJ╔╫⌡K1∩        fú~A▌c▄mÑ┴?ôQ╩ƒⁿ|╨{ç▒·ΘB╡Φτ▌⌠─╘q?nⁿC/v>σ°┬#'L┌ 0Kè£
    ╩[Érekx«wë,\¥─K\a╡·┐PDIF╩l╤YH╞F$c6≈G¡Üc^r=pbiµΦ┘±ÿ▓zΦ¿0░ì┐á7┌o■«-ⁿ#,

While decoding i.e at line unp.decode('utf8') gives me the following error

    Traceback (most recent call last):
      File "nic_dycrypt_encrypt.py", line 99, in 
        print('Ciphertext:', AESCipher(key).decrypt(ciphertext))
      File "nic_dycrypt_encrypt.py", line 86, in decrypt
        decode = unp.decode('utf8').strip()
      File "C:\Python27\lib\encodings\utf_8.py", line 16, in decode
        return codecs.utf_8_decode(input, errors, True)
    UnicodeDecodeError: 'utf8' codec can't decode byte 0xaf in position 3: invalid start byte

Please any one help me to know what is that format and why the error is coming and how to resolve