正在学习Python，但是在Learn Python The Hard Way Exercise 20中，按照作者给出的代码，我在Powershell上运行，得到的输出结果是这样的：

First let's print the whole file:

a aaaaaaaa
aaaaaaaaaaaa
aaaaaaaaaaaa

Now let's rewind, kind of like a tape.
Let's print three lines:
a aaaaaaaa
aaaaaaaaaaaa
aaaaaaaaaaaa

可是本来应该是这样的：

$ python ex20.py test.txt
First let's print the whole file:

This is line 1
This is line 2
This is line 3

Now let's rewind, kind of like a tape.
Let's print three lines:
1 This is line 1

2 This is line 2

3 This is line 3

哪里出问题了？