def calc_gene_length(file_path):
    """Read in a FASTA file and calculate sequence length.

    Assumes a typical one line header for a FASTA file.

    **Parameters**

    file_path : str
        Path to FASTA file

    **Returns**

    seq_len : int
        length of gene
    """
    with open(file_path) as handle:
        handle.readline()  # skip FASTA header
        seq = handle.read()  # read file into single string
        seq = seq.replace('\n', '')  # remove line breaks
    seq_len = len(seq)
    return seq_len