我正在创建一个读取文件的程序，如果文件的第一行不为空白，它将读取接下来的四行。在这些行上执行计算，然后读取下一行。如果该行不为空，则继续。但是，我收到此错误：

ValueError: invalid literal for int() with base 10: ''.

它正在读取第一行，但无法将其转换为整数。

我该怎么做才能解决此问题？

代码：

file_to_read = raw_input("Enter file name of tests (empty string to end program):")
try:
    infile = open(file_to_read, 'r')
    while file_to_read != " ":
        file_to_write = raw_input("Enter output file name (.csv will be appended to it):")
        file_to_write = file_to_write + ".csv"
        outfile = open(file_to_write, "w")
        readings = (infile.readline())
        print readings
        while readings != 0:
            global count
            readings = int(readings)
            minimum = (infile.readline())
            maximum = (infile.readline())