Question

I am writing a small app that has to perform some ‘sanity checks’ before entering execution. (eg. of a sanity check: test if a certain path is readable / writable / exists)

The code:

import logging
import os
import shutil
import sys
from paths import PATH

logging.basicConfig(level=logging.DEBUG)
log = logging.getLogger('sf.core.sanity')

def sanity_access(path, mode):
    ret = os.access(path, mode)
    logfunc = log.debug if ret else log.warning
    loginfo = (os.access.__name__, path, mode, ret)
    logfunc('%s(\'%s\', %s)==%s' % loginfo)
    return ret

def sanity_check(bool_func, true_func, false_func):
    ret = bool_func()
    (logfunc, execfunc) = (log.debug, true_func) if ret else \
        (log.warning, false_func)
    logfunc('exec: %s', execfunc.__name__)
    execfunc()

def sanity_checks():
    sanity_check(lambda: sanity_access(PATH['userhome'], os.F_OK), \
                 lambda: None, sys.exit)

My question is related to the sanity_check function.

This function takes 3 parameters (bool_func, true_func, false_func). If the bool_func (which is the test function, returning a boolean value) fails, true_func gets executed, else the false_func gets executed.

1) lambda: None is a little lame , because for example if the sanity_access returns True, lambda: None gets executed, and the output printed will be:

DEBUG:sf.core.sanity:access('/home/nomemory', 0)==True
DEBUG:sf.core.sanity:exec: <lambda>

So it won’t be very clear in the logs what function got executed. The log will only contain <lambda> . Is there a default function that does nothing and can be passed as a parameter ? Is it a way to return the name of the first function that is being executed inside a lambda ?

Or a way not to log that “exec” if ‘nothing’ is sent as a paramter ?

What’s the none / do-nothing equivalent for functions ?

sanity_check(lambda: sanity_access(PATH['userhome'], os.F_OK), \
                 <do nothing, but show something more useful than <lambda>>, sys.exit)

Additional question, why is lambda: pass instead of lambda: None not working ?

Answer 1

What’s with all the lambdas that serve no purpose? Well, maybe optional arguments will help you a bit:

def sanity_check( test, name='undefined', ontrue=None, onfalse=None ):
    if test:
        log.debug(name)
        if ontrue is not None:
            ontrue()
    else:
        log.warn( name )
        if onfalse is not None:
            onfalse()

def sanity_checks():
    sanity_check(sanity_access(PATH['userhome'], os.F_OK), 'test home', 
        onfalse=sys.exit)

But you are really overcomplicating things.