from Bio import SeqIO

def sequence_length(fasta):
    """
    return a dict of the lengths of sequences in a fasta file
    """
    file_handle = open(fasta)
    in_handle = SeqIO.parse(file_handle, "fasta")
    records = {record.id: len(record) for record in in_handle}
    file_handle.close()
    return records

from Bio import SeqIO

def sequence_length(fasta):
    """
    return a dict of the lengths of sequences in a fasta file
    """
    sequences = SeqIO.parse(fasta, "fasta")
    records = {record.id: len(record) for record in sequences}
    return records

def sequence_names(fasta):
    """
    return a list of the sequence IDs in a FASTA file
    """
    sequences = SeqIO.parse(fasta, "fasta")
    records = [record.id for record in sequences]
    return records

Add function to get list of sequence names from a FASTA file.
Add function to get list of sequence names from a FASTA file.

Refactor to be simpler.
