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Fix performance of streaming long text #14941

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Merged
krassowski merged 3 commits into from
Aug 6, 2025
Merged

Fix performance of streaming long text #14941

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4b298ad
Add a failing test for stream performance
krassowski Jul 19, 2025
0bd8e20
Fix the performance issue
krassowski Jul 19, 2025
9482534
Merge branch 'main' into fix-printing-speed
krassowski Jul 19, 2025
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2 changes: 1 addition & 1 deletion IPython/core/history.py
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Original file line number Diff line number Diff line change
Expand Up @@ -590,7 +590,7 @@ class HistoryOutput:
output_type: typing.Literal[
"out_stream", "err_stream", "display_data", "execute_result"
]
bundle: typing.Dict[str, str]
bundle: typing.Dict[str, str | list[str]]


class HistoryManager(HistoryAccessor):
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4 changes: 2 additions & 2 deletions IPython/core/interactiveshell.py
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Expand Up @@ -3063,11 +3063,11 @@ def write(data, *args, **kwargs):
output_stream = outputs[-1]
if output_stream is None:
output_stream = HistoryOutput(
output_type=output_type, bundle={"stream": ""}
output_type=output_type, bundle={"stream": []}
)
outputs_by_counter[execution_count].append(output_stream)

output_stream.bundle["stream"] += data # Append to existing stream
output_stream.bundle["stream"].append(data) # Append to existing stream
return result

stream.write = write
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6 changes: 4 additions & 2 deletions IPython/core/magics/basic.py
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Expand Up @@ -571,9 +571,11 @@ def notebook(self, s):
for output in outputs[execution_count]:
for mime_type, data in output.bundle.items():
if output.output_type == "out_stream":
cell.outputs.append(v4.new_output("stream", text=[data]))
text = data if isinstance(data, list) else [data]
cell.outputs.append(v4.new_output("stream", text=text))
elif output.output_type == "err_stream":
err_output = v4.new_output("stream", text=[data])
text = data if isinstance(data, list) else [data]
err_output = v4.new_output("stream", text=text)
err_output.name = "stderr"
cell.outputs.append(err_output)
elif output.output_type == "execute_result":
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10 changes: 10 additions & 0 deletions tests/test_interactiveshell.py
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Expand Up @@ -16,6 +16,7 @@
import shutil
import sys
import tempfile
import time
import unittest
import pytest
from unittest import mock
Expand Down Expand Up @@ -84,6 +85,15 @@ def test_run_cell_multiline(self):
self.assertEqual(res.success, True)
self.assertEqual(res.result, None)

def test_stream_performance(self):
"""It should be fast to execute."""
src = "for i in range(250_000): print(i)"
start = time.perf_counter()
ip.run_cell(src)
end = time.perf_counter()
duration = end - start
assert duration < 10

def test_multiline_string_cells(self):
"Code sprinkled with multiline strings should execute (GH-306)"
ip.run_cell("tmp=0")
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