The single star `*`

unpacks the sequence/collection into positional arguments, so you can do this:

```
def sum(a, b):
return a + b
values = (1, 2)
s = sum(*values)
```

This will unpack the tuple so that it actually executes as:

```
s = sum(1, 2)
```

The double star `**`

does the same, only using a dictionary and thus named arguments:

```
values = { 'a': 1, 'b': 2 }
s = sum(**values)
```

You can also combine:

```
def sum(a, b, c, d):
return a + b + c + d
values1 = (1, 2)
values2 = { 'c': 10, 'd': 15 }
s = sum(*values1, **values2)
```

will execute as:

```
s = sum(1, 2, c=10, d=15)
```

Also see section 4.7.4 – Unpacking Argument Lists of the Python documentation.

Additionally you can define functions to take `*x`

and `**y`

arguments, this allows a function to accept any number of positional and/or named arguments that aren’t specifically named in the declaration.

Example:

```
def sum(*values):
s = 0
for v in values:
s = s + v
return s
s = sum(1, 2, 3, 4, 5)
```

or with `**`

:

```
def get_a(**values):
return values['a']
s = get_a(a=1, b=2) # returns 1
```

this can allow you to specify a large number of optional parameters without having to declare them.

And again, you can combine:

```
def sum(*values, **options):
s = 0
for i in values:
s = s + i
if "neg" in options:
if options["neg"]:
s = -s
return s
s = sum(1, 2, 3, 4, 5) # returns 15
s = sum(1, 2, 3, 4, 5, neg=True) # returns -15
s = sum(1, 2, 3, 4, 5, neg=False) # returns 15
```