Merge 2 lines with delimiter

[Buddhism]

You use close() that's not needed when use with open and there is no write().
Here how it look if write result to file.

def line_concat(lst):
    temp = zip(lst[::2], lst[::-2])
    return [':'.join(i) for i in temp]

def file_read(file_in):
    with open(file_in) as f:
        lst = [line.strip() for line in f if not line.isspace()]
        return lst

if __name__ == '__main__':
    file_in = 'xy.txt'
    lst = file_read(file_in)
    #print(lst) # Test file read
    with open('xy_new.txt', 'w') as f_out:
        for line in line_concat(lst):
            f_out.write(f'{line}\n')

Thank you so much!
After some error on my side of files showing up blank, I got it with your help!

Cheers!