Single star *
Unpacking
We can use * to unpack arguments in a list or tuple.
Example:
nums = [1, 2, 3, 4 , 5]
def add_numbers(n1, n2, n3, n4, n5):
return n1 + n2 + n3 + n4 + n5
In order to run add_numbers() with the elements in nums list, we can pass each argument such as add_numbers(nums[0], nums[1], nums[2], nums[3], nums[4]). However, there is an easier way to do this by using * operator.
Using *
We can call the same function as add_numbers(*nums).
When using * in this case, the number of arguments for the function must be the same as the length of the list we unpack.
Another example with using Python’s built-in function range().
range(3, 6) # Calling `range()` with 3 and 6 as arguments
args = [3, 6]
# If we have `args` list, we can call `range()` as following:
range(*args)
Packing
We can use * to pack arguments in functions especially when we don’t know how many arguments may be passed.
def add_nums1(n1, n2, n3):
print(n1, n2, ,n3)
# Similar function, but this time with packing arguments
def add_nums2(*nums):
# Arguments passed come as a tuple. We can convert args tuple to a list
# nums_list = list(*nums)
print(nums) # prints (1, 2, 3)
print(*nums) # prints 1, 2, 3
Double stars **
Unpacking
The double stars ** can be used to unpack items in a dictionary.