all Python 3systerm

sys.stderr

streams

The standard error stream. Tracebacks and diagnostics go here so they do not mix with the result.

Syntax

print('ошибка', file=sys.stderr)

stderr is not block-buffered, so messages show up immediately even when stdout is redirected to a file. Judging systems usually compare stdout only: debug output to stderr does not spoil the answer, while output to stdout does. Write to it with print(..., file=sys.stderr).

Examples

import sys
print('debug: x = 42', file=sys.stderr)  # в поток ошибок, ответ не испорчен
print('42')  # → 42 — ответ идёт в stdout

See also

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