def freq_str(freq_list):

    """
    Function that transforms the array of frequency values into a string
    of comma separated entries.

    The array is converted into a string and the square brackets are removed
    form it. The resulting string will be the list of frequencies to sweep
    over, organized into comma separated entries.

    Parameters
    ----------
    freq_list: list
                List of frequencies to sweep over

    Returns
    -------
    freq_str: str
              String of comma separated frequencies to be inputted
              into the instrument
    """
    # Convert the frequency list into a string
    freq = str(freq_list)

    # Remove the square brackets from the string of frequencies
    freq_str = freq.split('[')[1].split(']')[0]

    return freq_str