Why do I get a ASCII encoding error with Unicode data in Python 2.4 but not in 2.7?

I have a program that, when run in Python 2.7, produces proper Unicode output to the sta开发者_如何学运维ndard output. When run in Python 2.4, I get UnicodeEncodeError: 'ascii' codec can't encode characters in position 1-4: ordinal not in range(128). What changed between version 2.4 and 2.7 that this works now?

Although I could not find any mention of it elswhere, it appears that Python 2.7 is automatically converting text to the terminal encoding, instead of throwing an error as expected.

Python 2.7:

> echo $LANG
en_US.UTF-8
> python -c 'import sys; print sys.getdefaultencoding()'
ascii

> python -c 'import sys; sys.stdout.write(u"\u03A3")'
Σ
> python -c 'import sys; sys.stdout.write(u"\u03A3".encode("utf8"))'
Σ

Python 2.6 (on another box)

> echo $LANG
en_US.UTF-8
> python -c 'import sys; print sys.getdefaultencoding()'
ascii

> python -c 'import sys;  sys.stdout.write(u"\u03A3")'
Traceback (most recent call last):
  File "<string>", line 1, in <module>
UnicodeEncodeError: 'ascii' codec cant encode character u'\u03a3' in position 0: ordinal not in range(128)
> python -c 'import sys;  sys.stdout.write(u"\u03A3".encode("utf8"))'
Σ

In any case, an .encode("utf8") on the data before output should avoid the issue.