python AES with CBC/PKCS5Padding

pycrypto_AES.py

from Crypto.Cipher import AES
from Crypto import Random
import base64

block_size = AES.block_size


#unpad = lambda s : s[0:-ord(s[-1])]

def pad(plain_text):
    """
    func to pad cleartext to be multiples of 8-byte blocks.

    If you want to encrypt a text message that is not multiples of 8-byte blocks, 
    the text message must be padded with additional bytes to make the text message to be multiples of 8-byte blocks.
    """
    number_of_bytes_to_pad = block_size - len(plain_text) % block_size
    ascii_string = chr(number_of_bytes_to_pad)
    padding_str = number_of_bytes_to_pad * ascii_string
    padded_plain_text =  plain_text + padding_str
    return padded_plain_text


key='some-key'
plain='plain_text'
plain = pad(plain)

iv = Random.new().read(AES.block_size)

cipher = AES.new(key, AES.MODE_CBC, iv )
encrypted_text = cipher.encrypt( plain )

print encrypted_text

How can we decrypt it ?

why import base64?