C W wrote: > Dear Python experts, > > I never figured out when to call a method with parenthesis, when is it > not? It seems inconsistent. > > For example, > If I do > >> data.isnull() > > numberair_pressure_9amair_temp_9amavg_wind_direction_9amavg_wind_speed_9am > max_wind_direction_9ammax_wind_speed_9amrain_accumulation_9am > rain_duration_9amrelative_humidity_9amrelative_humidity_3pm > 0 False False False False False False False False False False False > 1 False False False False False False False False False False False > 2 False False False False False False False False False False False > > Or I can do without parenthesis, >> data.isnull > > <bound method DataFrame.isnull of number air_pressure_9am > air_temp_9am avg_wind_direction_9am \ > 0 0 918.060000 74.822000 271.100000 > 1 1 917.347688 71.403843 101.935179 > 2 2 923.040000 60.638000 51.000000 > > > Obviously, the second case does not make any senses.
Let's try with our own class: >>> class A: ... def foo(self): return "bar" ... >>> a = A() >>> a.foo() 'bar' With parens the foo method is executed and returns the expected result whose repr() is then printed by the interactive interpreter. >>> a.foo <bound method A.foo of <__main__.A object at 0x7f0956a00eb8>> Without parens the repr() of the method is printed just like the repr of any other value would be. That repr() has the form <bound method CLASSNAME.METHODNAME REPR_OF_INSTANCE> and in your case REPR_OF_INSTANCE happens to be a lengthy dump of the DataFrame. To verify our findings let's define a custom __repr__ for out A: >>> class A: ... def foo(self): return "bar" ... def __repr__(self): return "yadda " * 10 ... >>> A().foo <bound method A.foo of yadda yadda yadda yadda yadda yadda yadda yadda yadda yadda > _______________________________________________ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
