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gh-151814: Add test for TextIOWrapper.write unbounded memory growth from repeated writes #152244

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gh-151814: Add test for TextIOWrapper.write unbounded memory growth from repeated writes #152244

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16 changes: 16 additions & 0 deletions Lib/test/test_io/test_textio.py
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Original file line number Diff line number Diff line change
Expand Up @@ -6,6 +6,7 @@
import sys
import threading
import time
import tracemalloc
import unittest
import warnings
import weakref
Expand Down Expand Up @@ -1522,6 +1523,21 @@ def write(self, data):
t.write("x"*chunk_size)
self.assertEqual([b"abcdef", b"ghi", b"x"*chunk_size], buf._write_stack)

def test_write_empty_no_memory_growth(self):
# gh-151814: Writing empty string should have stable memory usage.
t = self.TextIOWrapper(self.BytesIO())
nwrites = 200_000
tracemalloc.start()
try:
for _ in range(nwrites):
t.write("")
_, peak = tracemalloc.get_traced_memory()
finally:
tracemalloc.stop()

# No longer leaks several bytes per write.
self.assertLess(peak, nwrites)

def test_issue119506(self):
chunk_size = 8192

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