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diff --git a/rpython/tool/ansi_print.py b/rpython/tool/ansi_print.py
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index bfa40be..29dd332 100644
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--- a/rpython/tool/ansi_print.py
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+++ b/rpython/tool/ansi_print.py
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@@ -7,7 +7,7 @@ from py.io import ansi_print
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 from rpython.tool.ansi_mandelbrot import Driver
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-isatty = getattr(sys.stderr, 'isatty', lambda: False)
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+isatty = lambda: False
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 mandelbrot_driver = Driver()
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 wrote_dot = False     # global shared state
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