Why this code works in python3, but not python 2:

[Maciej Dziardziel]

Out of curiosity: Does anyone know why the code below is valid in python3, but not python2:

def foo(*args, bar=1, **kwargs):
pass

 

[alex23]

Out of curiosity: Does anyone know why the code below is valid in python3, but not python2:

def foo(*args, bar=1, **kwargs):
pass

It was an explicit syntax change for Python3. You can read about the
reasoning behind it here:

http://www.python.org/dev/peps/pep-3102/

 

[Chris Angelico]

Out of curiosity: Does anyone know why the code below is valid in python3, but not python2:

def foo(*args, bar=1, **kwargs):
pass

Keyword-only arguments are (IIRC) a Py3-only feature. There are lots
of features that don't work in Python 2 - that's simply the way things
happen with old versions of software.

ChrisA

 

[Joshua Landau]

Out of curiosity: Does anyone know why the code below is valid in python3, but not python2:

def foo(*args, bar=1, **kwargs):
pass

Python 3 gained syntax for keyword-only arguments.

Try "foo(1)" and it will fail -- "bar" needs to be given as a keyword.
This is because it comes after a *-expression. You can also do "def
foo(*, bar=1)" if you want bar to be keyword-only without accepting
any number of positional arguments. Python 2 does not have these, and
doesn't understand the syntax for them.

 

[Maciej Dziardziel]

It was an explicit syntax change for Python3. You can read about the
reasoning behind it here:

http://www.python.org/dev/peps/pep-3102/

Thanks, that was helpful.

Maciej Dziardziel

 

[alex23]

Try "foo(1)" and it will fail -- "bar" needs to be given as a keyword.

No it won't, because it is supplied with a default. You may be
confusing it with the requirement that `bar` must be given as a keyword
in order for it to override the default, compared to the way this would
need to be written in Py2:

def foo(bar=1, *args, **kwargs):
...

....in which case `bar` could be assigned to by the first positional
argument.

 

[Joshua Landau]

No it won't, because it is supplied with a default.

Pah! I'm not even thinking.