Remove some side effects and add an optional to save log to file as well.

README.rst

@@ -30,7 +30,16 @@ that uses the standard Python logging module will play along nicely.
 Behaviours
 ----------
 
--  Messages are always written to stderr.
+- Messages are always written to `stderr` if `glog` is used uninitialized.
+
+- By calling `glog.init(FILE_NAME)`, where FILE_NAME is a `str`, logs will be
+  saved to that file. Target files only need to be initialized once and could
+  be shared anywhere. Repeated initialization is supported, and all logs will
+  be added to that file only once.
+
+- Calling `glog.init("stderr")` or `glog.init("stdout")` will make glog log to
+  standard error or standard output.
+
 
 -  Lines are prefixed with a google-style log prefix, of the form
 
@@ -76,6 +85,19 @@ parsing flags, like so:
         log.init()
         main(posargs[1:])
 
+To show log and save a copy to file at the same time:
+
+.. code:: python
+
+    import glog as log
+
+    log.init("example.log")
+
+    log.info("It works.")
+    log.warn("Something not ideal")
+    log.error("Something went wrong")
+    log.fatal("AAAAAAAAAAAAAAA!")
+
 Happy logging!
 
 .. _twitter.common.log: https://github.com/twitter/commons/tree/master/src/python/twitter/common/log

glog.py

@@ -15,12 +15,17 @@
 * Your apps and scripts will all have a consistent log format, and the same
   predictable behaviours.
 
-This library configures the root logger, so nearly everything you import
-that uses the standard Python logging module will play along nicely.
-
 ## Behaviours
 
-* Messages are always written to stderr.
+* Messages are always written to `stderr` if `glog` is used uninitialized.
+
+* By calling `glog.init(FILE_NAME)`, where FILE_NAME is a `str`, logs will be
+  saved to that file. Target files only need to be initialized once and could
+  be shared anywhere. Repeated initialization is supported, and all logs will
+  be added to that file only once.
+
+* Calling `glog.init("stderr")` or `glog.init("stdout")` will make glog log to
+  standard error or standard output.
 
 * Lines are prefixed with a google-style log prefix, of the form
 
@@ -64,6 +69,7 @@ def main():
 
 Happy logging!
 """
+import sys
 
 import logging
 import time
@@ -74,6 +80,8 @@ def main():
                       short_name='v')
 FLAGS = gflags.FLAGS
 
+file_names = []
+
 
 def format_message(record):
     try:
@@ -112,10 +120,7 @@ def format(self, record):
         record.getMessage = lambda: record_message
         return logging.Formatter.format(self, record)
 
-logger = logging.getLogger()
-handler = logging.StreamHandler()
-
-level = logger.level
+logger = logging.getLogger("glog")
 
 
 def setLevel(newlevel):
@@ -124,17 +129,36 @@ def setLevel(newlevel):
     logger.debug('Log level set to %s', newlevel)
 
 
-def init():
+def init(filename=None):
+    logger.propagate = False
+    if filename is None:
+        if "stderr" not in file_names:
+            handler = logging.StreamHandler()
+            filename = "stderr"
+    elif filename in file_names:
+        # Do not add files that already has been added.
+        return
+    elif filename == "stderr":
+        handler = logging.StreamHandler(sys.stderr)
+    elif filename == "stdout":
+        handler = logging.StreamHandler(sys.stdout)
+    else:
+        handler = logging.FileHandler(filename)
+
+    file_names.append(filename)
+    handler.setFormatter(GlogFormatter())
+    logger.addHandler(handler)
     setLevel(FLAGS.verbosity)
 
-debug = logging.debug
-info = logging.info
-warning = logging.warning
-warn = logging.warning
-error = logging.error
-exception = logging.exception
-fatal = logging.fatal
-log = logging.log
+debug = logger.debug
+info = logger.info
+warning = logger.warning
+warn = logger.warning
+error = logger.error
+exception = logger.exception
+fatal = logger.fatal
+log = logger.log
+
 
 DEBUG = logging.DEBUG
 INFO = logging.INFO
@@ -143,6 +167,8 @@ def init():
 ERROR = logging.ERROR
 FATAL = logging.FATAL
 
+# basicConfig = logger.basicConfig
+
 _level_names = {
     DEBUG: 'DEBUG',
     INFO: 'INFO',
@@ -166,6 +192,4 @@ def init():
     """) % ''.join(_level_letters)
 """Regex you can use to parse glog line prefixes."""
 
-handler.setFormatter(GlogFormatter())
-logger.addHandler(handler)
-setLevel(FLAGS.verbosity)
+init()