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The alexber.utils.stdlogging module provides a StreamToLogger adapter and the initStream() helper that replaces a stream (typically sys.stderr or sys.stdout) with a logger-backed object. Every line written to the stream is forwarded to a Python logging.Logger. This is particularly useful in Docker containers and other environments where application logs must be captured from a single stream.

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initStream()

The preferred API for redirecting a stream to a logger. 
import logging
from alexber.utils.stdlogging import initStream

log = logging.getLogger('stderr')
initStream(logger=log, logger_level=logging.ERROR)

# sys.stderr is now backed by the logger
import sys
print('something went wrong', file=sys.stderr)  # routed to log.error(...)

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Parameters

ParameterTypeDefaultDescription
loggerlogging.Loggerlogging.getLogger('stderr')Logger that receives the stream output.
logger_levelint or strlogging.ERRORLevel at which lines are logged. Accepts integer constants (logging.INFO) or strings ("INFO").
stream_gettercallableReturns sys.stderrSupplier that returns the stream to be wrapped.
stream_settercallableSets sys.stderrConsumer that installs the wrapped stream.
adapter_clstype or strStreamToLoggerAdapter class to use. Can be a class or a dotted import string.
As of v0.13.11, logger_level accepts both string level names ("INFO", "DEBUG") and integer constants (logging.INFO). String values are normalised to uppercase before lookup.

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StreamToLogger

The adapter class that implements the stream interface and forwards writes to a logger. You generally do not need to instantiate this directly — use initStream() instead. 
from alexber.utils.stdlogging import StreamToLogger
import logging
import sys

log = logging.getLogger('stdout')
sl = StreamToLogger(logger=log, stream=sys.stdout, logger_level=logging.INFO)
sys.stdout = sl

print('hello')  # calls log.info('hello')

​
Constructor parameters

ParameterRequiredDescription
loggerYesA logging.Logger or compatible logger object.
streamYesThe original stream being wrapped (sys.stderr, sys.stdout, etc.). Used only for flush().
logger_level / log_levelNoLog level. Defaults to logging.DEBUG.

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Methods

  • write(lines) — Splits lines on newlines and logs each non-empty line at log_level.
  • flush() — Delegates to the original stream’s flush() method.

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Redirecting stderr in Docker

In a Docker container, application logs are typically collected from the container’s stdout/stderr streams. If your application uses Python’s logging module with a file handler or a structured formatter, those logs never reach Docker’s log collector. Redirecting sys.stderr to a logger bridges the gap.
1

Configure the logging system

import logging

logging.basicConfig(
    level=logging.DEBUG,
    format='%(asctime)s %(name)s %(levelname)s %(message)s',
)
2

Redirect stderr to the logger

from alexber.utils.stdlogging import initStream
import logging

initStream(
    logger=logging.getLogger('stderr'),
    logger_level=logging.ERROR,
)
After this call, anything written to sys.stderr — including unhandled exception tracebacks — is logged through the configured logging system.
3

Optionally redirect stdout as well

import sys

initStream(
    logger=logging.getLogger('stdout'),
    logger_level=logging.INFO,
    stream_getter=lambda: sys.stdout,
    stream_setter=lambda s: setattr(sys, 'stdout', s),
)
Redirecting sys.stdout is fragile. Some C extensions and third-party libraries write directly to the underlying file descriptor and will bypass the logger. Redirect sys.stderr first; only redirect sys.stdout if you have a specific need.

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Using a string log level

from alexber.utils.stdlogging import initStream

# String levels are accepted since v0.13.11
initStream(logger_level='WARNING')
initStream(logger_level='debug')   # case-insensitive

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