Why is the program not printing three lines?

[Souvik Dutta]

Ooo thanks I understood.

On Thu, 19 Mar, 2020, 8:10 pm Pieter van Oostrum, <pieter-l at vanoostrum.org>
wrote:

> Souvik Dutta <souvik.viksou at gmail.com> writes:
>
> > I should have been more clear
> > class first():
> >     print("from first")
> >     def second():
> >         print("from second")
> > first()
> >
> > When I run the above code the output is
> > "from first"
>
> And where do you think this comes from? Are you thinking this comes from
> the call 'first()'?
> If so, that is not correct. See my Demo below.
> It is from the class definition.
>
> Run only this code, and you will see it also print "from first":
>
> class first():
>     print("from first")
>     def second():
>         print("from second")
>
> > (2ND CODE)
> >
> > class first():
> >     print("from first")
> >     def second():
> >         print("from second")
> > first.second()
> >
> > When I run this code the output is
> > "from first"
> > "from second"
> >
> > Thus going by the above logic
>
> Which logic?
>
> > class first():
> >     print("from first")
> >     def second():
> >         print("from second")
> > first()
> > first.second()
> >
> > This should have given the following output
> > from first
> > from first
> > from second
>
> No, because this is not the combination of the first two codes. To have
> this combination, you should include the class definition twice.
>
> > That is I should have got from first 2 times. But instead I got this
> output.
> > from first
> > from second
> > Why is this so?
>
> 'From first' is the result of the class definition. 'from second' is the
> result of first.second().
> And first() doesn't produce any output.
>
> Your problem is probably that you think that the call first() executes all
> the statements in the class definition. It doesn't. That's not how Python
> class definitions work.
>
> Check the Demo below another time.
>
> > On Thu, Mar 19, 2020, 5:30 PM Pieter van Oostrum <
> pieter-l at vanoostrum.org>
> > wrote:
> >
> >> Chris Angelico <rosuav at gmail.com> writes:
> >>
> >> > Creating the class runs all the code in the class block, including
> >> > function definitions, assignments, and in this case, a print call.
> >> >
> >> > Classes are not declarations. They are executable code.
> >>
> >> Demo:
> >>
> >> In [26]: class first():
> >>      ...     print("From first")
> >>      ...     def second():
> >>      ...         print("From second")
> >> From first
> >>
> >> You see, the print "From first" occurs at class definition time.
> >>
> >> In [27]: first()
> >> Out[27]: <__main__.first at 0x10275f880>
> >>
> >> Calling the class (i.e. creating an instance) doesn't print anything,
> >> because the print statement is not part of the class __init__ code.
> >>
> >> In [28]: first.second()
> >> From second
> >>
> >> That's expected.
> >>
> >> In [29]: first.second()
> >> From second
> >>
> >> Again.
>
> --
> Pieter van Oostrum
> www: http://pieter.vanoostrum.org/
> PGP key: [8DAE142BE17999C4]
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>