替换文本文件python中的列

Question

我有一个包含多个列的.txt文件，我想替换另一列的第一列。我正在尝试以下方法：

JD[] #Are the data for which I want to replace the first column of the file.

with open('filedata.txt', 'r') as f:
        print f.readline().rstrip('\n')

        for value, line in zip(JD, f)
                  elements = line.split()
                  A = format(value,elements[1:])

np.savetxt(A)