`print()` doesn't accept the double starred expression `*v` and `f-strings` doesn't accept the single and double starred expression `*v` and `**v`

[hyperkai]

Bug report

Bug description:

print() accepts the single starred expression *v as shown below:

v = ['A', 'B', 'C', 'D', 'E']

print(*v)
# A B C D E

But print() doesn't accept the double starred expression **v as shown below:

v = {'name':'John', 'age':36}

print(**v)
# TypeError: 'name' is an invalid keyword argument for print()

So, print() should accept the double starred expression **v, displaying the output as shown below:

v = {'name':'John', 'age':36}

print(**v)
# name:John age:36

And, f-strings doesn't accept the single and double starred expression *v and **v as shown below:

v = ['A', 'B', 'C', 'D', 'E']

print(f'{*v}')
print(f'{*v=}')
# SyntaxError: can't use starred expression here

v = {'name':'John', 'age':36}

print(f'{**v}')
print(f'{**v=}')
# SyntaxError: f-string: expecting a valid expression after '{'

So, f-strings should accept the single and double starred expression *v and **v, displaying the outputs as shown below:

v = ['A', 'B', 'C', 'D', 'E']

print(f'{*v}')
# A B C D E

print(f'{*v=}')
# *v=A B C D E

v = {'name':'John', 'age':36}

print(f'{**v}')
# name:John age:36

print(f'{**v=}')
# **v=name:John age:36

CPython versions tested on:

3.12

Operating systems tested on:

Windows

[serhiy-storchaka]

print() accepts the double starred syntax form:

>>> v = {'sep': ':', 'end': ']\n'}
>>> print(1, 2, **v)
1:2]

Nothing accepts "the single and double starred expression", because they are not expressions. They can be used as a part of syntax of some expressions, (for example a function call), but they are not expressions, as ,v and /v are not expressions.

If you propose to add new syntax, part of which is the single and double starred syntax forms, this should be first discussed on https://discuss.python.org/c/ideas/6. You must provide good reasons why the new syntax is needed.

[skirpichev]

But print() doesn't accept the double starred expression **v as shown below:

That's because it's exactly follows it's signature:

>>> inspect.signature(print)
<Signature (*args, sep=' ', end='\n', file=None, flush=False)>

So, print() should accept the double starred expression **v, displaying the output as shown below:

That means you suggest to change print() signature like this:

>>> def myprint(*args, sep=' ', end='\n', file=None, flush=False, **kwargs):
...     print(kwargs, *args,  sep=sep, end=end, file=file, flush=flush)
...     
>>> myprint(**{'name':'John', 'age':36})
{'name': 'John', 'age': 36}

But what if your dict has a "sep" key?

And, f-strings doesn't accept the single and double starred expression *v and **v as shown below:

Again, it's well documented:
https://docs.python.org/3/reference/lexical_analysis.html#f-strings

If you want to change Python syntax - that should be discussed first on https://discuss.python.org/c/ideas/6.

[StanFromIreland]

@hyperkai Please read the documentation carefully before opening issues, this is seems to happen quite frequently.

[skirpichev]

@hyperkai, please also read @AA-Turner comment here: #137629 (comment) For me it seems you entirely ignore his advice. Phrasing like "should do" especially don't make sense in feature requests like this.