我们可以在 return 语句中使用逻辑运算符吗

Question

Can I use the not operator in this case and output the else as false using not operator

 # NEW TO PYTHON
 def is_positive(number):
  if number > 0:
    return bool(number)
  else:
    return not bool(number)

Answer 1

Yes you can.

But a better code would look like that:

def is_positive(number):
    return (number > 0)

Your code returns True if number == 0 , even if it enters the else section, since bool(number) always return True if number != 0 . If you want that, use >= instead of > .

In your code, you're calculating two boolean values, while one is enough. You're calculating a boolean number > 0 , and if it is True , you're calculating a new boolean that will always be True if the first condition is valid, and same for the else statement, so it's like writing:

def is_positive(number):
    if number > 0:
        return True
    else:
        return False

Now you can see more clearly that if number > 0 is True , it returns True , and if number > 0 is False , it returns False . But number > 0 is by itself a boolean statement that evaluates to True and False . For example, if you know number > 0 , your code is equivalent to:

def is_positive(number):
    if True:
        return True
    else:
        return False

And if not:

def is_positive(number):
    if False:
        return True
    else:
        return False

So as you can see, you can directly return number > 0 .

Answer 2

Yes. you can. bool function will return true with any number except zero (even negative one). But this code is not good. you can do it in many better ways. The best way is to do it like this.

def is_positive(number):
    return (number > 0)

If is a statement that does this: If the condition was true do this else do that. In your code, it is like this: if the condition was true, return true else return false. So you can simply say return the answer of the condition instead of saying if it was true return true. if the number is positive, the answer to number > 0 will become true so it's simply like to say return true and if not, the answer to the condition will become false so it's like to say return false. Actually, when you call this method, it will check the condition first. if it was true, it is replaced with true and if not, it is replaced with false.

Answer 3

You cannot, Syntactically speaking: you can. the program will compile, However. it will work differently than you think.

Every number except for a zero converted into a bool gives True .