Using the @traced decorator

Release:1.2.1

Warning

The @traced decorator will not work as you might expect when it decorates a function (method) in the body of a class. In general, prefer to decorate the class itself, explicitly identifying the method names to trace if the default (all class, static, and instance methods, excluding “__special__” methods, with the exception of __init__ and __call__) doesn’t suit your needs.

Trace all methods of a class using a module-named logger

This is the simplest way to use the autologging.traced decorator. All non-special methods of the class are traced to a logger that is named after the containing module and class. (Note: the special __init__ method is an exception to the rule - it is traced by default if it is defined.)

Note

Inherited methods are never traced. If you want tracing for inherited methods, either trace them in the super class, or override and trace them in the subclass.

# my_module.py

from autologging import traced


@traced
class MyClass:

   def __init__(self):
      self._value = "ham"

   def my_method(self, arg, keyword=None):
      return "%s, %s, and %s" % (arg, self._value, keyword)
>>> import logging, sys
>>> from autologging import TRACE
>>> logging.basicConfig(level=TRACE, stream=sys.stdout,
...     format="%(levelname)s:%(name)s:%(funcName)s:%(message)s")
>>> from my_module import MyClass
>>> my_obj = MyClass()
TRACE:my_module.MyClass:__init__:CALL *() **{}
TRACE:my_module.MyClass:__init__:RETURN None
>>> my_obj.my_method("spam", keyword="eggs")
TRACE:my_module.MyClass:my_method:CALL *('spam',) **{'keyword': 'eggs'}
TRACE:my_module.MyClass:my_method:RETURN 'spam, ham, and eggs'
'spam, ham, and eggs'

Trace all methods of a class using a user-named logger

This example is identical to the above example, except that the tracing logger has a user-defined name (“tracing.example” in this case). Simply pass the user-defined logger as the first positional argument to traced:

# my_module.py

import logging
from autologging import traced


@traced(logging.getLogger("tracing.example"))
class MyClass:

   def __init__(self):
      self._value = "ham"

   def my_method(self, arg, keyword=None):
      return "%s, %s, and %s" % (arg, self._value, keyword)
>>> import logging, sys
>>> from autologging import TRACE
>>> logging.basicConfig(level=TRACE, stream=sys.stdout,
...     format="%(levelname)s:%(name)s:%(funcName)s:%(message)s")
>>> from my_module import MyClass
>>> my_obj = MyClass()
TRACE:tracing.example.MyClass:__init__:CALL *() **{}
TRACE:tracing.example.MyClass:__init__:RETURN None
>>> my_obj.my_method("spam", keyword="eggs")
TRACE:tracing.example.MyClass:my_method:CALL *('spam',) **{'keyword': 'eggs'}
TRACE:tracing.example.MyClass:my_method:RETURN 'spam, ham, and eggs'
'spam, ham, and eggs'

Trace only certain methods of a class

The traced decorator accepts a variable number of positional string arguments. As you saw in the previous example, passing a user-defined logger as the first argument allows you to specify the parent logger for tracing. You may also pass a variable number of method names as arguments to traced. Autologging will then trace only the methods that are named (assuming that they are defined in the class body). And as in the previous example, you may still choose whether or not to pass in a named logger as the first argument (not shown below).

# my_module.py

from autologging import traced


@traced("my_method", "__eq__")
class MyClass:

   def __init__(self):
      self._value = "ham"

   def my_method(self, arg, keyword=None):
      return "%s, %s, and %s" % (arg, self._value, keyword)

   def __eq__(self, other):
      return False
>>> import logging, sys
>>> from autologging import TRACE
>>> logging.basicConfig(level=TRACE, stream=sys.stdout,
...     format="%(levelname)s:%(name)s:%(funcName)s:%(message)s")
>>> from my_module import MyClass
>>> my_obj = MyClass()  # __init__ is not in the list, so not traced
>>> my_obj.my_method("spam", keyword="eggs")
TRACE:my_module.MyClass:my_method:CALL *('spam',) **{'keyword': 'eggs'}
TRACE:my_module.MyClass:my_method:RETURN 'spam, ham, and eggs'
'spam, ham, and eggs'
>>> my_obj == 79  # __eq__ is explicitly named in the list
TRACE:my_module.MyClass:__eq__:CALL *(79,) **{}
TRACE:my_module.MyClass:__eq__:RETURN False
False

Trace a generator iterator

New in version 1.2.0.

Generator functions employ the yield keyword in the function body, instructing Python to create (and return) a generator iterator when the function is invoked:

# my_module.py

from autologging import traced


@traced
class MyClass:

    def my_iter(self, word):
        for character in reversed(word):
            yield character.upper()

To observe how Autologging traces both the generator and its returned generator iterator, assume we run the program like so:

>>> import logging, sys
>>> from autologging import TRACE
>>> logging.basicConfig(level=TRACE, stream=sys.stdout,
...     format="%(levelname)s:%(name)s:%(funcName)s:%(message)s")
>>> from my_module import MyClass
>>> my_obj = MyClass()
>>> for c in my_obj.my_iter("spam"):
...     print(c)
...
(continued below)

Because the generator function my_iter is traced, Autologging will dutifully emit the CALL/RETURN trace logging records:

TRACE:my_module.MyClass:my_iter:CALL *('spam',) **{}
TRACE:my_module.MyClass:my_iter:RETURN <generator object MyClass.my_iter at 0x7f54f4043840>
(continued below)

In versions of Autologging prior to 1.2.0, this would be the only tracing output. But as of version 1.2.0, the generator iterator is now traced as well, and will emit additional YIELD/STOP trace logging records:

TRACE:my_module.MyClass:my_iter:YIELD 'M'
M
TRACE:my_module.MyClass:my_iter:YIELD 'A'
A
TRACE:my_module.MyClass:my_iter:YIELD 'P'
P
TRACE:my_module.MyClass:my_iter:YIELD 'S'
S
TRACE:my_module.MyClass:my_iter:STOP

Trace a nested class

Tracing a nested class is no different than tracing a module-level class:

# my_module.py

from autologging import traced


class MyClass:

   @traced
   class Nested:

      def do_something(self):
         pass

Note

Under Python 3.3+, Autologging will use a class’s qualified name (PEP 3155) when creating loggers. In this example, the tracing log entries will be logged using the name “my_module.MyClass.Nested”. (Under versions of Python <3.3, where “__qualname__” is not available, the logger name would be simply “my_module.Nested”.)

>>> import logging, sys
>>> from autologging import TRACE
>>> logging.basicConfig(level=TRACE, stream=sys.stdout,
...     format="%(levelname)s:%(name)s:%(funcName)s:%(message)s")
>>> from my_module import MyClass
>>> nested = MyClass.Nested()
>>> nested.do_something()
TRACE:my_module.MyClass.Nested:do_something:CALL *() **{}
TRACE:my_module.MyClass.Nested:do_something:RETURN None

Trace a function using a module-named logger

# my_module.py

from autologging import traced


@traced
def my_function(arg, keyword=None):
   return "%s and %s" % (arg, keyword)
>>> import logging, sys
>>> from autologging import TRACE
>>> logging.basicConfig(level=TRACE, stream=sys.stdout,
...     format="%(levelname)s:%(name)s:%(funcName)s:%(message)s")
>>> from my_module import my_function
>>> my_function("spam", keyword="eggs")
TRACE:my_module:my_function:CALL *('spam',) **{'keyword': 'eggs'}
TRACE:my_module:my_function:RETURN 'spam and eggs'
'spam and eggs'

Trace a function using a user-named logger

# my_module.py

import logging
from autologging import traced


@traced(logging.getLogger("my.app"))
def my_function(arg, keyword=None):
   return "%s and %s" % (arg, keyword)
>>> import logging, sys
>>> from autologging import TRACE
>>> logging.basicConfig(level=TRACE, stream=sys.stdout,
...     format="%(levelname)s:%(name)s:%(funcName)s:%(message)s")
>>> from my_module import my_function
>>> my_function("spam", keyword="eggs")
TRACE:my.app:my_function:CALL *('spam',) **{'keyword': 'eggs'}
TRACE:my.app:my_function:RETURN 'spam and eggs'
'spam and eggs'

Trace a nested function

# my_module.py

from autologging import traced


def my_function(arg, keyword=None):
   @traced
   def nested_function(word1, word2):
      return "%s and %s" % (word1, word2)
   return nested_function(arg, keyword if (keyword is not None) else "eggs")
>>> import logging, sys
>>> from autologging import TRACE
>>> logging.basicConfig(level=TRACE, stream=sys.stdout,
...     format="%(levelname)s:%(name)s:%(funcName)s:%(message)s")
>>> from my_module import my_function
>>> my_function("spam")
TRACE:my_module:nested_function:CALL *('spam', 'eggs') **{}
TRACE:my_module:nested_function:RETURN 'spam and eggs'
'spam and eggs'