Programming in C I used to have code sections only used for debugging purposes (logging commands and the like). Those statements could be completely disabled for production by using #ifdef pre-processor directives, like this:
#ifdef MACRO
controlled text
#endif /* MACRO */
What is the best way to do something similar in python?
If you just want to disable logging methods, use the logging module. If the log level is set to exclude, say, debug statements, then logging.debug will be very close to a no-op (it just checks the log level and returns without interpolating the log string).
If you want to actually remove chunks of code at bytecode compile time conditional on a particular variable, your only option is the rather enigmatic __debug__ global variable. This variable is set to True unless the -O flag is passed to Python (or PYTHONOPTIMIZE is set to something nonempty in the environment).
If __debug__ is used in an if statement, the if statement is actually compiled into only the True branch. This particular optimization is as close to a preprocessor macro as Python ever gets.
Note that, unlike macros, your code must still be syntactically correct in both branches of the if.
To show how __debug__ works, consider these two functions:
def f():
if __debug__: return 3
else: return 4
def g():
if True: return 3
else: return 4
Now check them out with dis:
>>> dis.dis(f)
2 0 LOAD_CONST 1 (3)
3 RETURN_VALUE
>>> dis.dis(g)
2 0 LOAD_GLOBAL 0 (True)
3 JUMP_IF_FALSE 5 (to 11)
6 POP_TOP
7 LOAD_CONST 1 (3)
10 RETURN_VALUE
>> 11 POP_TOP
3 12 LOAD_CONST 2 (4)
15 RETURN_VALUE
16 LOAD_CONST 0 (None)
19 RETURN_VALUE
As you can see, only f is "optimized".