def complement(pattern):
    """Compute the complementary string of pattern, with every nucleotide being replaced by its complement.

    Args:
        pattern (str): a DNA string pattern.

    Returns:
        String, a DNA string pattern in complementary with the given pattern.

    Examples:
        Return the complementary string of a pattern string.
        
        >>> pattern = 'AAAACCCGGT'
        >>> complementary_pattern = complement(pattern)
        >>> complementary_pattern
            'TTTTGGGCCA'
    """
    complement_dict = {"A": "T", "C": "G", "G": "C", "T": "A"}
    complement_pattern = "".join(complement_dict[i] for i in pattern)
    return complement_pattern