anonymous function objects?

[Uwe Mayer]

Is it possible to specify anonymous functions, something like:
hello world


in Pyton?
Lambda expressions don't work here.

Thanks,
Uwe

 

[Paul Rubin]

hello world

in Pyton? Lambda expressions don't work here.

Closest you can come is:

f = lambda: sys.stdout.write("hello world\n")

Of course if you're trying to capture the function in a named variable
like f, just use a def statement.

 

[Uwe Mayer]

Closest you can come is:

f = lambda: sys.stdout.write("hello world\n")

Ah. )
Why does the "print" statement return a syntax error here?
File "<stdin>", line 1
lambda: print("hallo")
^
SyntaxError: invalid syntax

Of course if you're trying to capture the function in a named variable
like f, just use a def statement.

Unfortunately I want to assign a handler function to an object and something
like this does not work:
File "<stdin>", line 1
def a.handler():
^
SyntaxError: invalid syntax

But wrapping print into a myprint function works


Thanks,
Ciao
Uwe

 

[gabriele renzi]

Uwe Mayer ha scritto:

Ah. )
Why does the "print" statement return a syntax error here?
^^^^^^^^^

this is the reason
You can't have statements into an expression

 

[Peter Hansen]

Unfortunately I want to assign a handler function to an object and something
like this does not work:


File "<stdin>", line 1
def a.handler():
^
SyntaxError: invalid syntax

But this does work, or something close to it:
.... print 'in handler'
....Traceback (most recent call last):
in handler


-Peter

 

[Michele Simionato]

Uwe Mayer:

Why does the "print" statement return a syntax error here?

Google for "Python regrets" where Guido admits that
'print' should have been a function.

Michele Simionato

 

[Uwe Mayer]

Uwe Mayer:

Google for "Python regrets" where Guido admits that
'print' should have been a function.

Will this change in future - and if not, why not?

Ciao
Uwe

 

[Bengt Richter]

But this does work, or something close to it:

... print 'in handler'
...
Traceback (most recent call last):

in handler

Or you can doctor up a Foobar that treats all
function attributes of its instances as methods
to be bound to the specific instance, e.g.,
(not tested beyond what you see)
... def __getattribute__(self, attr):
... sentinel = object()
... atto = object.__getattribute__(self, '__dict__').get(attr, sentinel)
... if hasattr(atto, '__get__'): return atto.__get__(self, type(self))
... elif atto is sentinel: return object.__getattribute__(self, attr)
... return atto
... Traceback (most recent call last):
File "<stdin>", line 1, in ?
'ordinary'

Try another Foobar instance:
Traceback (most recent call last):
File "<stdin>", line 1, in ?
g's own handler for <__main__.Foobar object at 0x02EF134C>

BTW new.instancemethod(handler, f) seems to duplicate handler.__get__(f),
leaving out the type(f) in handler.__get__(f, type(f)) that would make a bound method,
which is what it is, and which could be set as attribute of anything.

Note the difference between newh which sticks with the f
passed to new.instancemethod, and real, which Foobar.__getattribute__
dynamically attaches to the selected instance:
('real', <__main__.Foobar object at 0x02EF134C>)
^^^^^^^^^^

IOW, a plain callable has __get__ and gets bound to the instance,
whereas a bound method doesn't have __get__ any more, so it gets
retrieved as a plain attribute. BTW, to get an ordinary function call
for a function attribute of a Foobar instance, you'd have to
eliminate the function's __get__ effect one way or another,
e.g. staticmethod (which really wraps the function with a descriptor,
substituting its own __get__, which Foobar.__getattribute__ uses transparently)

>>> def sm(firstarg='sm first arg', *args): return firstarg, args ...
>>> g.sm = staticmethod(sm)
>>> g.sm() ('sm first arg', ())
>>> g.sm

>>> g.__dict__['sm']

>>> g.__dict__['sm'].__get__

>>> g.__dict__['sm'].__get__(g)

<function sm at 0x02EE8E9C>

Regards,
Bengt Richter

 

[Michele Simionato]

I have not access to Guido's time machine!

M. S.