Python if( ): vs if:

Question

On Code Academy there is this course where in the example they show

def speak(message):
    return message

if happy():
    speak("I'm happy!")
elif sad():
    speak("I'm sad.")
else:
    speak("I don't know what I'm feeling.")

The above example will NOT be related to the rest of the code I show. That was just an example for the if statement. Now I was under the impression that when ever writing an if statement it had to end in an ():like the above example.

However when doing the assignments this does not work:

def shut_down(s):
    if s == "yes"():
        return "Shutting down"
    elif s == "no"():
        return "Shutdown aborted"
    else:
        return "Sorry"

However this works:

def shut_down(s):
    if s == "yes":
        return "Shutting down"
    elif s == "no":
        return "Shutdown aborted"
    else:
        return "Sorry"

My question is how come the () is not needed next to the "yes" and "no" but :is still needed. I thought whenever writing an if statement it will automatically have to end with ():. In that very first example, that's how it is shown. Do you understand my confusion.

No, that's not the case. See [what the official tutorial says about the `if` statement](https://docs.python.org/3/tutorial/controlflow.html#if-statements). — Dan Getz, Jul 29 '15 at 20:05
It looks like you have a fundamental misunderstanding about [functions](https://docs.python.org/3.4/tutorial/controlflow.html#defining-functions) and [`if` statements](https://docs.python.org/3.4/tutorial/controlflow.html#if-statements). — TigerhawkT3, Jul 29 '15 at 20:05
Happy and sad are probably [functions](http://stackoverflow.com/a/19131217/5031339) — NightShadeQueen, Jul 29 '15 at 20:06
@chrisaycock I think you're thinking of a different kind of assignment than the OP — StephenTG, Jul 29 '15 at 20:07

score 5 · Answer 1 · answered Jul 29 '15 at 20:06

5

In the example given, happy() and sad() are functions, and as such require parentheses. The if itself does not need parentheses at the end (and it shouldn't have them)

answered Jul 29 '15 at 20:06

StephenTG

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Aaron McDaid · Answer 2 · 2015-07-30T12:19:53.647

4

No, if has nothing to do with ()

happy is a function. happy() is a call to that function. So, if happy(): tests if the happy function returns true when called.

In other words, if happy(): speak("I'm happy!") is equivalent to

result_of_happy = happy()
if result_of_happy:
    speak("I'm happy!")

edited Jul 30 '15 at 12:19

answered Jul 29 '15 at 20:07

Aaron McDaid

26,501
9
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score 2 · Answer 3 · answered Jul 29 '15 at 20:26

As has been mentioned happy() / sad() are functions so they require (). In example two of your question you are comparing your value to the string "yes" because it is a string it does not require ().

Within an if statement you can use parentheses to make the code more readable and ensure certain operations are evaluated before others.

if (1+1)*2 == 4:
    print 'here'
else:
    print 'there'

Differs from:

if 1+1*2 == 4:
    print 'here'
else:
    print 'there'

score 0 · Answer 4 · answered Sep 23 '18 at 06:27

Because string objects are not callable so what are you expecting then:

Then use lambda not that efficient tho:

def shut_down(s):
    if (lambda: s == "yes")():
        return "Shutting down"
    elif (lambda: s == "no")():
        return "Shutdown aborted"
    else:
        return "Sorry"

Python if( ): vs if:

4 Answers4

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