def yield_FASTA(f):

    header, seq = '', ''

    for line in f:
        if line.startswith('>'):
            if header:
                yield (header, seq)
                header, seq = line, ''
            else:
                header = line

        else:
            seq += filter( lambda x: not x.isdigit() and not x.isspace(), line )

    yield (header, seq)

with open('fasta.txt') as f:
    for i in yield_FASTA(f):
        print i



#Using this example fasta.txt
'''
> Fake Line
AGCTACGACTAGCCGCGCGCTATATACTAGCATCGACATTTTTATATTAAGACGAGACTATCATATACTAGCGAGCGCGGCACTATATTTGCTCGACTACACAGCCATCAAGATCAACACATATATACTTCCCCTATACACCAACACAGCGGGGACGAATACTATCATCATCATCATCAGCGCGCGCGCAGCAGAGGAAGGAAGGAATTCCTCTACTCTATTTATAGACGCGASAGCAG
> New Line
AGTAGAT
> Cat
> Doghead
AGTCG
GAT
GGG
C
GAGTCAG
> Noodles
G
'''