Python 将数据写入文本文件，然后中途更改

我试图将数据写入下一个文件，但中途更改了列的一个值，该值对于第一组行是常量。这是我的代码：

import random
import time

start_time = time.time() #time measurement
numpoints = 512
L = 20
d = 1
points = set()

# Open f and write
with open("question2.xyz","w") as f:
    f.write("%d\ncomment goes here\n" % numpoints) #this is for the 2nd line in my xyz 
    while len(points) < numpoints:
        p = (random.randint(0, L), random.randint(0, L), random.randint(0, L))
        if p not in points:
            points.add(p)
            f.write('H %f %f %f\n' % p)

提前谢谢你的帮助

编辑，woops抱歉，这是我想要实现的

512 #number of
comment goes here
H 6.000000 19.000000 14.000000
H 11.000000 2.000000 7.000000
H 15.000000 20.000000 16.000000
O 6.000000 19.000000 14.000000
O 11.000000 2.000000 7.000000
O 15.000000 20.000000 16.000000

---

现在，我的代码为所有512行的第一个值输入H，从第256行开始，我需要将其更改为O，您可以使用一个生成器生成点，并使用两个

进行
循环：

def pointgen(used):
    while True:
        p = (random.randint(0, L), random.randint(0, L), random.randint(0, L))
        if p not in used:
            used.add(p)
            yield p

# Open f and write
with open("question2.xyz","w") as f:
    f.write("%d\ncomment goes here\n" % numpoints) #this is for the 2nd line in my xyz 
    pg = pointgen(points)
    for i in xrange(numpoints // 2):
        f.write('H %f %f %f\n' % pg.next())
    for i in xrange(numpoints // 2):
        f.write('O %f %f %f\n' % pg.next())

您还可以发布您希望实现的示例吗？您可以发布示例输入文件和预期输出吗..没有输入文件，将生成该文件并显示如上所示的输出文件
def pointgen(used):
    while True:
        p = (random.randint(0, L), random.randint(0, L), random.randint(0, L))
        if p not in used:
            used.add(p)
            yield p

# Open f and write
with open("question2.xyz","w") as f:
    f.write("%d\ncomment goes here\n" % numpoints) #this is for the 2nd line in my xyz 
    pg = pointgen(points)
    for i in xrange(numpoints // 2):
        f.write('H %f %f %f\n' % pg.next())
    for i in xrange(numpoints // 2):
        f.write('O %f %f %f\n' % pg.next())