On 17/06/18 19:02, C W wrote:
> I never figured out when to call a method with parenthesis, when is it not?
You call anything in Python (function, method, class, etc) using
parentheses. The parentheses are what makes it a call.
When you don't use parentheses you are referencing the
callable object.
>> data.isnull()
That calls the isnull method of data
>> data.isnull
That references the isnull method, so you could store it in a variable
for future use:
checkNull = data.isnull
# do other stuff.
if checkNull(): # call data.isnull() via the variable
# do more stuff
> <bound method DataFrame.isnull of number air_pressure_9am
And thats what the return value says - its a method.
> air_temp_9am avg_wind_direction_9am \
> 0 0 918.060000 74.822000 271.100000
But I've no idea why you get this output...
> Obviously, the second case does not make any senses.
The fact that its a method makes sense, the "data" makes no sense.
> But, in data.columns,
> it is only correct to do without parenthesis as below:
>
>> data.columns
>
> Index(['number', 'air_pressure_9am', 'air_temp_9am', 'avg_wind_direction_9am',
So data.columns is not a method but an attribute.
The attribute apparently references an Index object.
> # with parenthesis throws an error
>> data.columns()
We've already established that data.columns is a reference
to an Index object and you can't call an Index object,
it is not "callable"
Traceback (most recent call
> last)<ipython-input-16-05cf52d0a56e> in <module>()----> 1
> data.columns()
> TypeError: 'Index' object is not callable
Which is what Python is telling you.
> I always thought columns(), isnull() are methods to objects,
isnull is apparenmtly a method.
columns is apparenmtly an attribute.
They are different things and you need to read the
documentation (or code) to see which is which.
You can call a method.
You can only call an attribute if it stores a callable object.
And if you use a method name without parens you
get a reference to the method back.
--
Alan G
Author of the Learn to Program web site
http://www.alan-g.me.uk/
http://www.amazon.com/author/alan_gauld
Follow my photo-blog on Flickr at:
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