StringIO current stream position after object creation seems to be wrong?

Question

I am struggling with the current stream position of StringIO objects. I create a StringIO object with initial content. Then when adding strings with write() the content gets overwritten.

f = io.StringIO("some initial text data")

f.write(' and some strings and other stuff')

print(f.getvalue())

yields to

 and some strings and other stuff

Checking the current stream position after object creation:

f = io.StringIO("some initial text data")
f.tell()

gives

0

That's pretty confusing. I expected the stream position at the end of 'some initial text data'. I can calculate the length of the initial string and then set the position manually with f.seek(initial_string_length) But this seems cumbersome.

Are there any other ideas?
And is this the intended behaviour of StringIO objects?

Answer 1

From the docs:

The stream is positioned at the start of the buffer

f.seek(0, 2) did the trick. Or better f.seek(0, SEEK_END)