Python equivalent for #ifdef DEBUG

Question

In C we write code like

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#ifdef DEBUG printf("Some debug log... This could probably be achieved by python logging.Logger"); /* Do some sanity check code */ assert someCondition /* More complex sanitycheck */ while(list->next){ assert fooCheck(list) }  #endif 

Is there a way to do this in python?

Edit: I got my answer, and more :) Paolo, Steven Rumbalski and J Sebastian gave me the information I was looking for. Thanks das for the detailed answer, although I'll probably not use a preprocessor right now.

J Sebastian, whose comment got deleted because the answer in which he posted his comment, deleted his answer I think. He said I could use the isEnabledFor() method in Logger to feed a conditional.

Thanks everyone for your inputs. This is my first question. I wish I could accept paolo, or j sebastian's answers. But since those were offered as comments, I'll accept das' answer.

I will probably use either http://nestedinfiniteloops.wordpress.com/2012/01/15/if-debug-python-flavoured/ or Logger.isEnabledFor()

Answer 1

Use __debug__ in your code:

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if __debug__:     print 'Debug ON' else:     print 'Debug OFF' 

Create a script abc.py with the above code and then

1. Run with python -O abc.py
2. Run with python abc.py

Observe the difference.

Answer 2

Mohammad's answer is the right approach: use if __debug__.

In fact, Python completely removes the if statement if the expression is a static constant (such as True, False, None, __debug__, 0, and 0.0), making if __debug__ a compile-time directive rather than a runtime check:

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>>> def test(): ...     if __debug__: ...         return 'debug' ...     return 'not debug' ... >>> import dis >>> dis.dis(test)   3           0 LOAD_CONST               1 ('debug')               2 RETURN_VALUE 

The -O option is explained in detail in the python documentation for command line options, and there is similar optimization for assert statements.

So don't use an external preprocessor—for this purpose, you have one built in!