Python将不会使用readlines（）和for循环删除第一行来重写文件

Question

I' writing a web scraping script in Python that pulls an 'ID' from the first line of a text file and appends it to a partial URL; then downloads an image from said URL. Everything works fine, but when I run it using the third function (which contains the actual code for downloading - this works fine) it doesn't update the text file by deleting the first line.

I'm sure there is something I am missing here, and any help would be greatly appreciated.

def delete_used_id():
    # open and save all ids
    id_file_r = open('C:/Users/my.name/Documents/IDs.txt', 'r')
    lines = id_file_r.readlines()
    first_line_unf = str(lines[0])[3:]
    first_line = first_line_unf.strip()
    id_file_r.close()
    # reopen in write mode
    id_file_w = open('C:/Users/my.name/Documents/IDs.txt','w')
    for unused_id in lines:
        if unused_id != first_line:
            id_file_w.write(unused_id)
    id_file_w.close()
    print("Deleting used ID: " + first_line)

def get_id_from_file():
    id_file = open('C:/Users/my.name/Documents/IDs.txt', 'r')
    # slice the first 3 chars off of the string
    farmer_id_unf = id_file.readline()[3:]
    farmer_id = farmer_id_unf.strip()
    print("Getting Farmer ID: " + farmer_id)
    return farmer_id

Answer 1

Thanks to jonrsharpe and nerdwaller:

ANSWER:

def delete_used_id():
    # open and save all ids
    id_file_r = open('C:/Users/my.name/Documents/IDs.txt', 'r')
    lines = id_file_r.readlines()
    first_line_unf = lines[0][3:]
    first_line = first_line_unf.strip()
    id_file_r.close()
    # reopen in write mode
    id_file_w = open('C:/Users/my.name/Documents/IDs.txt','w')
    for line in lines[1:]:
        id_file_w.write(line)
    id_file_w.close()
    print("Deleting used ID: " + first_line)