python can't count!

[Dominik Kaspar]

hello

i'm wondering if i'm just too stupid for python or if i've missed
something fundamentally important of its semantics.
Why does the following program result in the TypeError: print_it()
takes exactly 1 argument (2 given)?
I don't see any function passing or receiving 2 arguments here... am i
blind?

import threading

class Server(threadin g.Thread):
def print_it(n):
print n

def run(self):
self.print_it(3 4)
while 1:
pass

s = Server()
s.start()

[Jay O'Connor]

Re: python can't count!

On 2 Oct 2003 08:02:48 -0700, dokaspar@studen t.ethz.ch (Dominik
Kaspar) wrote:
[color=blue]
>hello
>
>i'm wondering if i'm just too stupid for python or if i've missed
>something fundamentally important of its semantics.
>Why does the following program result in the TypeError: print_it()
>takes exactly 1 argument (2 given)?
>I don't see any function passing or receiving 2 arguments here... am i
>blind?[/color]

You are missing the hidden passing of 'self' to object methods in
Python. Methods need to declare 'self' in the parameter list

...
def print_it (self, n):
print n
...




[color=blue]
>
>import threading
>
>class Server(threadin g.Thread):
> def print_it(n):
> print n
>
> def run(self):
> self.print_it(3 4)
> while 1:
> pass
>
>s = Server()
>s.start()[/color]

[Christopher Koppler]

Re: python can't count!

On 2 Oct 2003 08:02:48 -0700, dokaspar@studen t.ethz.ch (Dominik
Kaspar) wrote:
[color=blue]
>hello
>
>i'm wondering if i'm just too stupid for python or if i've missed
>something fundamentally important of its semantics.
>Why does the following program result in the TypeError: print_it()
>takes exactly 1 argument (2 given)?
>I don't see any function passing or receiving 2 arguments here... am i
>blind?
>
>import threading
>
>class Server(threadin g.Thread):
> def print_it(n):
> print n
>
> def run(self):
> self.print_it(3 4)
> while 1:
> pass
>
>s = Server()
>s.start()[/color]

You're calling print_it as an instance method, and thus should have
def'd it as print_it(self, n)




--Christopher

[Terry Reedy]

Re: python can't count!


"Dominik Kaspar" <dokaspar@stude nt.ethz.ch> wrote in message
news:62e9c66e.0 310020702.7d0e0 2b7@posting.goo gle.com...[color=blue]
> i'm wondering if i'm just too stupid for python[/color]

Not if you understand the answers you get to the next question ;-)
[color=blue]
> or if i've missed something fundamentally important
> of its semantics.[/color]

Yes. instance.method (args) abbreviates
instance-class-or-superclass.meth od(instance, args). So
[color=blue]
> class Server(threadin g.Thread):
> def print_it(n):
> print n
> def run(self):
> self.print_it(3 4)[/color]

translates, in this case, to Server.print_it (self, 34), a call with 2
args.

The abbreviation is possible because instances know what class they
are instances of. The abbreviation is handy because is saves a few
keystrokes. It is important because is allows you to call a method on
an instance without specifying (or even necessarily knowing) where in
the class inheritance hierarchy it is defined, and it allows a call to
continue to work even when that place changes. For instance, after[color=blue]
>s = Server()[/color]
,[color=blue]
>s.start()[/color]
translates into Thread.start(s) . However, after adding method

def start(self):
<add code to log start time>
Tread.start(sel f)

to Server, the same s.start() call would instead translate to
Server.start(se lf) with no change to the method call!

Terry J. Reedy

[Kyler Laird]

Re: python can't count!

dokaspar@studen t.ethz.ch (Dominik Kaspar) writes:
[color=blue]
>i'm wondering if i'm just too stupid for python or if i've missed
>something fundamentally important of its semantics.[/color]

The later.

It'll get easier.

--kyler