python写文件,过滤空行,根据某一行打上标记

import shutil
import os


###第一步写文件
'''
with open('test.txt', 'w',encoding='utf-8') as f:
    f.write("1111111111\n")
    f.write("2222222222\n")
    f.write("3333333333\n")

    f.write("aaaaaaa\r\n")
    f.write("bbbbbbb\r\n")
    f.write("ccccccc\r\n")
'''

###第二步 过滤文件空行，再重新写入新的文件
file_data=''
i=0
with open('test.txt', 'r', encoding='utf-8') as f:
    for line in f.readlines():
        print(str(i) + " line=" + line + str(line != '') + str(len(line)))   ## debug

        line = line.strip()
        if(len(line) > 1):   ## 判断条件,过滤空行
            file_data += line
            file_data += '\r\n'
        i = i + 1
        #print(str(i) + " line="+line)   #打印查看每一行的内容

with open('test5.txt', "w", encoding="utf-8") as f:
    f.write(file_data)
    print('文件创建成功！')

'''
思路：在某一行打上"#"标记，根据行号来标记
i = 0


if i > 31 and i < 34:
    line = '#' + line
    print(line)
file_data += line + '\r\n'
i += 1
        
'''