This answer is a bit of a cheat, but currently Biopython doesn't expose the FASTQ quality string decoding functionality in the public API:
from Bio import SeqIO
from StringIO import StringIO
fastq_string = "@%s\n%s\n+\n%s\n" % (id1, seq1, qual1)
record = SeqIO.read(StringIO(fastq_string), "fastq-illumina")
i am merging overlapping paired end sequences