How to convert 'binary string' to normal string in Python3?

For example, I have a string like this(return value of subprocess.check_output):

    >>> b'a string'
    b'a string'

Whatever I did to it, it is always printed with the annoying b' before the string:

    >>> print(b'a string')
    b'a string'
    >>> print(str(b'a string'))
    b'a string'

Does anyone have any ideas about how to use it as a normal string or convert it into a normal string?

Decode it.

    >>> b'a string'.decode('ascii')
    'a string'

To get bytes from string, encode it.

    >>> 'a string'.encode('ascii')
    b'a string'