Why can’t I use multiple *vars in tuple unpacking on the left-hand side of an assignment?

I am trying to make sense of starred expressions in python. When I use it in python functions, it allows to call functions with different number of arguments:

def my_sum(*args):
    results = 0
    for x in args:
        results += x
    return results

print(my_sum(1,2,3))
>>6

print(my_sum(1,2,3,4,5,6,7))]
>>28

However when I use it in an assignment, it works like this:

a, b, *c, d = [1,2,3,4,5,6,7,8,9,10]
print(a,b,c,d)

>>1 2 [3, 4, 5, 6, 7, 8, 9] 10

*a, b, *c, d = [1,2,3,4,5,6,7,8,9,10]
print(a,b,c,d)

*a, b, *c, d = [1,2,3,4,5,6,7,8,9,10]
^
SyntaxError: multiple starred expressions in assignment

Can someone explain to me what is happening behind this assignment that doesn’t allow multiple starred expressions?

Answer

The language doesn’t allow this because it would be ambiguous, and allowing ambiguities is contrary to the Zen of Python:

In the face of ambiguity, refuse the temptation to guess.

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Let’s say you run:

*a, b, *c, d = [1,2,3,4,5,6,7,8,9,10]

One way to interpret that would be:

a = [1,2,3,4,5,6,7]
b = 8
c = [9]
d = 10

Another would be:

a = [1]
b = 2
c = [3,4,5,6,7,8,9]
d = 10

Yet another would be:

a = []
b = 1
c = [2,3,4,5,6,7,8,9]
d = 10

Python refuses to guess: It simply declares the code invalid.