如何让我的Python脚本更快？

I'm pretty new to Python, and I have written a (probably very ugly) script that is supposed to randomly select a subset of sequences from a fastq-file. A fastq-file stores information in blocks of four rows each. The first row in each block starts with the character "@". The fastq file I use as my input file is 36 GB, containing about 14,000,000 lines.I'm pretty new to Python, and I have written a