[New-bugs-announce] [issue45076] open "r+" problem

[otn]

New submission from otn <ootani.takashi at gmail.com>:

For opened file as "r+", even if write() then readline(), readline() is executed first.

When add tell() after write(), it works correctly.

==========================================
data1 = "aa\nbb\ncc\n"
data2 = "xx\n"

with open("data.txt","w") as f:
    f.write(data1)

with open("data.txt","r+") as f:
    f.write(data2)
#   f.tell()
    print("Line:",repr(f.readline()))

with open("data.txt") as f:
    print("All:",repr(f.read()))
==========================================
OUTPUT:
Line: 'aa\n'
All: 'aa\nbb\ncc\nxx\n'

EXPECTED:
Line: 'bb\n'
All: 'xx\nbb\ncc\n'

----------
components: IO
messages: 400826
nosy: otn
priority: normal
severity: normal
status: open
title: open "r+" problem
type: behavior
versions: Python 3.9

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue45076>
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