def merge_vcfs(vcf_file, merged_mut_file):
    """
    This module will accept the vcf files for mutect and radia read into memory in a dict object
    VCF_FILE and will merge the calls.  Merged calls are printed to MERGED_MUT_FILE.

    VCF_FILE is a dict with
    key : mutation caller (mutect or radia)
    value : dict with
            key: (chrom, pos, ref, alt)
            value: vcf line in list form (split by tab)
    """
    mutect_keys = set(vcf_file['mutect'].keys())
    radia_keys = set(vcf_file['radia'].keys())
    common_keys = radia_keys.intersection(mutect_keys)
    # Open as append since the header is already written
    with open(merged_mut_file, 'a') as outfile:
        for mutation in common_keys:
            print('\t'.join(vcf_file['radia'][mutation]), file=outfile)
    return None