New submission from Albert Zeyer:
The doc says that StringIO.truncate should not change the current position.
Consider this code:
try:
import StringIO
except ImportError:
import io as StringIO
buf = StringIO.StringIO()
assert_equal(buf.getvalue(), "")
print("buf: %r" % buf.getvalue())
buf.write("hello")
print("buf: %r" % buf.getvalue())
assert_equal(buf.getvalue(), "hello")
buf.truncate(0)
print("buf: %r" % buf.getvalue())
assert_equal(buf.getvalue(), "")
buf.write("hello")
print("buf: %r" % buf.getvalue())
assert_equal(buf.getvalue(), "\x00\x00\x00\x00\x00hello")
buf.truncate(0)
print("buf: %r" % buf.getvalue())
assert_equal(buf.getvalue(), "")
On Python 3.6, I get the output:
buf: ''
buf: 'hello'
buf: ''
buf: '\x00\x00\x00\x00\x00hello'
On Python 2.7, I get the output:
buf: ''
buf: 'hello'
buf: ''
buf: 'hello'
Thus it seems that Python 2.7 StringIO.truncate does actually resets the
position for this case or there is some other bug in Python 2.7. At least from
the doc, it seems that the Python 3.6 behavior is the expected behavior.
----------
components: IO
messages: 292866
nosy: Albert.Zeyer
priority: normal
severity: normal
status: open
title: StreamIO truncate behavior of current position
versions: Python 2.7
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Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue30250>
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