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(threading.Thread):
def print_it(n):
print n

def run(self):
self.print_it(34)
while 1:
pass

s = Server()
s.start()

 

[Jay O'Connor]

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?

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
...

 

[Christopher Koppler]

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(threading.Thread):
def print_it(n):
print n

def run(self):
self.print_it(34)
while 1:
pass

s = Server()
s.start()

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




--Christopher

 

[Terry Reedy]

i'm wondering if i'm just too stupid for python

Not if you understand the answers you get to the next question ;-)

or if i've missed something fundamentally important
of its semantics.

Yes. instance.method(args) abbreviates
instance-class-or-superclass.method(instance, args). So

class Server(threading.Thread):
def print_it(n):
print n
def run(self):
self.print_it(34)

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

s = Server() ,
s.start()

translates into Thread.start(s). However, after adding method

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

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

Terry J. Reedy

 

[Kyler Laird]

i'm wondering if i'm just too stupid for python or if i've missed
something fundamentally important of its semantics.

The later.

It'll get easier.

--kyler