Python在打开的文件末尾添加了新行

Question

While writing some tests, i got stuck on some weird behavior. I finally narrow the problem to file opening. For instance, this one, my.dat :

one line
two lines and no final line break

I then ran that python code:

with open('my.dat') as fd:
    assert fd.read()[-1] == '\n'

With both python 3 and 2, this code does not raise any AssertError.

My question is: why forcing the presence of line jump at the end of files ?

Answer 1

It works here. Are you 100% sure that there is not actually a newline at the end of your file? Because many text editors (atom, notepad++) automatically add newlines at the end of a file.

>>> open('a.txt', 'w').write('blabla')
6
>>> open('a.txt', 'r').read()
'blabla'
>>> assert open('a.txt', 'r').read()[-1] == '\n'
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AssertionError