Python 2.7 sometimes yields IOError: [Errno 0] Error on Windows

• OS version and name: Windows 10 64-bit
• Hyper.app version: 1.4.8 (stable)
• The issue is reproducible in vanilla Hyper.app: Yes

Issue

Printing to the console with Python 2 sometimes results in an IOError: [Errno 0] on Windows. This issue seems to appear only on Windows when opening a file for both reading and writing, quote:

When the "r+", "w+", or "a+" access type is specified, both reading and writing are allowed (the file is said to be open for "update"). However, when you switch between reading and writing, there must be an intervening fflush, fsetpos, fseek, or rewind operation. The current position can be specified for the fsetpos or fseek operation, if desired.

Relevant StackOverflow answer here.

Running this script almost certainly causes the error at some point:

# py -2.7 test.py
for i in range(5000):
  print('foo')

Output:

[...]
foo
foo
fTraceback (most recent call last):
  File "test.py", line 5, in <module>
    print('foo')
IOError: [Errno 0] Error

I am using Python 2.7.14 (v2.7.14:84471935ed, Sep 16 2017, 20:25:58) [MSC v.1500 64 bit (AMD64)] on win32. I can not reproduce this with any other terminal (tested Windows default terminal & ConEmu).

It appears as if the standard output was broken or handled incorrectly when running Python from inside a Hyper terminal. To me it seems this must have a root cause unrelated to Python. When that cause is found, feel free to rename the title of this issue.

Start by reproducing the failure in Hyper.app on Windows with Python 2.7 using the test.py loop shown in the issue, then compare it with the other terminals mentioned. Trace how Hyper handles console output during repeated writes and verify the issue is resolved when the script completes without IOError: [Errno 0] Error.