When reading in sequences, you may want to arrange or index them in some way (rather than just get one big list o' sequences). Fortunately Biopython's SeqIO has a useful function for this: "to_dict" returns a dictionary where the keys are derived from the SeqRecords that are the values.

index_sequence.py

from Bio import SeqIO

handle = open("example.fasta", "rU")
record_dict = SeqIO.to_dict (SeqIO.parse (handle, "fasta"))
handle.close()

# you now have dict where the keys are the sequence IDs, e.g. record_dict["gi:12345678"]

# you can index in other ways with the "key_function".
# for example, if you wanted to index by the description of the sequence
handle = open("example.fasta", "rU")
record_dict = SeqIO.to_dict (SeqIO.parse (handle, "fasta"), key_function=lambda s: s.description)
handle.close()