python - 以附加模式将子进程输出转储到文件中

Question

我必须将子进程的输出转储到以附加模式打开的文件

from subprocess import Popen

fh1 = open("abc.txt", "a+") # this should have worked as per my understanding

# fh1.readlines() # Adding this solves the problem 

p = Popen(["dir", "/b"], stdout = fh1, shell=True)

print p.communicate()[0]
fh1.close()

但是上面的代码覆盖了我不想要的文件 abc.txt，取消注释 fh1.readlines() 会将光标移动到适当的位置，这是一个临时解决方案

我缺少什么基本的东西吗？

In [18]: fh1 = open("abc.txt",'a')

In [19]: fh1.tell() # This should be at the end of the file
Out[19]: 0L

In [20]: fh1 = open("abc.txt",'r')

In [21]: print fh1.readlines()
['1\n', '2\n', '3\n', '4\n', '5\n']

Answer 1

将光标放在文件末尾而不读取文件的一种简单易行的方法是使用:

fh1.seek(2)
# .seek(offset, [whence]) >> if offset = 2 it will put the cursor in the given position relatively
# to the end of the file. default 'whence' position is 0, so at the very end