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If you want to check that a variable is explicitly True or False (and is not truthy/falsy), use is ( if variable is True ). If you want to check if a variable is equal to 0 or if a list is empty, use if variable == 0 or if variable == [] .
Bool(None) happens to be False, so it is not surprising when the code does not return anything. However, x has been assigned the value of None, so the second statement is also False and the code returns nothing. To check whether the statements are equivalent, we can run a few more statements through python to check.
In Python, None has nothing to do with values 0 or False. Loosely speaking, an undefined variable is something whose value is None. But None is also a valid Python object which is well defined.
if result is None:
print "error parsing stream"
elif result:
print "result pass"
else:
print "result fail"
keep it simple and explicit. You can of course pre-define a dictionary.
messages = {None: 'error', True: 'pass', False: 'fail'}
print messages[result]
If you plan on modifying your simulate function to include more return codes, maintaining this code might become a bit of an issue.
The simulate might also raise an exception on the parsing error, in which case you'd either would catch it here or let it propagate a level up and the printing bit would be reduced to a one-line if-else statement.
Don't fear the Exception! Having your program just log and continue is as easy as:
try:
result = simulate(open("myfile"))
except SimulationException as sim_exc:
print "error parsing stream", sim_exc
else:
if result:
print "result pass"
else:
print "result fail"
# execution continues from here, regardless of exception or not
And now you can have a much richer type of notification from the simulate method as to what exactly went wrong, in case you find error/no-error not to be informative enough.
Never, never, never say
if something == True:
Never. It's crazy, since you're redundantly repeating what is redundantly specified as the redundant condition rule for an if-statement.
Worse, still, never, never, never say
if something == False:
You have not. Feel free to use it.
Finally, doing a == None is inefficient. Do a is None. None is a special singleton object, there can only be one. Just check to see if you have that object.
There are many good answers. I would like to add one more point. A bug can get into your code if you are working with numerical values, and your answer is happened to be 0.
a = 0
b = 10
c = None
### Common approach that can cause a problem
if not a:
print(f"Answer is not found. Answer is {str(a)}.")
else:
print(f"Answer is: {str(a)}.")
if not b:
print(f"Answer is not found. Answer is {str(b)}.")
else:
print(f"Answer is: {str(b)}")
if not c:
print(f"Answer is not found. Answer is {str(c)}.")
else:
print(f"Answer is: {str(c)}.")
Answer is not found. Answer is 0.
Answer is: 10.
Answer is not found. Answer is None.
### Safer approach
if a is None:
print(f"Answer is not found. Answer is {str(a)}.")
else:
print(f"Answer is: {str(a)}.")
if b is None:
print(f"Answer is not found. Answer is {str(b)}.")
else:
print(f"Answer is: {str(b)}.")
if c is None:
print(f"Answer is not found. Answer is {str(c)}.")
else:
print(f"Answer is: {str(c)}.")
Answer is: 0.
Answer is: 10.
Answer is not found. Answer is None.
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