Python：从fastq.gz文件中提取特定长度的reads，生成fastq（一）

提取特定长度的reads，初始版本，只适合小文件，25000条reads需要十几分钟：

import glob
import gzip
length=[]
with gzip.open('test.fq.gz','rt') as fp:
    i = 0 
    for line in fp:
        i += 1
        if i % 4 == 2: 
            if len(line)-1==20:
                length.append(i)
output_fasta = open("temp.fq",'w')
def WRIRE():  
    N= 0       
    with gzip.open('test.fq.gz','rt') as fp:
        for line in fp:
            N += 1
            if N == i-1: 
                output_fasta.write(line)
            elif N == i: 
                output_fasta.write(line)
            elif N == i+1: 
                output_fasta.write(line)
            elif N == i+2: 
                output_fasta.write(line)
for i in length:
    WRIRE()
output_fasta.close()  
end = time.time()
print("used %s s" % str(end - start))