Replacing i with increasing numbers

August 29, 2023

I’m brand new to python so I apologize in advance. I need help renaming hundreds of files.

Currently my files look like this:
SRR3521304001.fastq
SRR3521305001.fastq
SRR3521306001.fastq
…

I would like my files to be renamed into the following format:
SRR3521304_S(i)_L001_R1.fastq
SRR3521305_S(i)_L001_R1.fastq
SRR3521306_S(i)_L001_R1.fastq
…

I need i to be a number that starts at 1 and increases.

This is what I have tried so far:

import os

files = os.listdir('joined_reads')
i = 1

for file in files:
    name = file.replace('001.fastq','S{i}_L100_R1_001.fastq')
    os.system('cp,   joined_reads/' + file + ' new/' + name)
    i+=1

This gives me files that look like SRR3521304_S(i)_L001_R1.fastq. Can someone help me change the i to an increasing number?

>Solution :

To use {i} you need to use f before your string to format it accordingly. Also you could use enumerate with the start value at 1.

import os

files = os.listdir('joined_reads')

for i, file in enumerate(files, 1):
    name = file.replace('001.fastq',f'S{i}_L100_R1_001.fastq')
    os.system('cp,   joined_reads/' + file + ' new/' + name)