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Asterisk

  1. Unpacking Using * (Combining Different Iterables AND Netsted Unpacking)
  2. Unpacking Using ** for dictionary literals
  3. Asterisks In Functions (Unpacking In Functions AND Packing In Functions)
  4. Keyword-Only Arguments With Positional Arguments
  5. Keyword-Only Arguments Without Positional Arguments

1. Unpacking a list/tuple/set using the *.​

nums = [i for i in range(1, 6)]

# a will be 1 and b will be a list containing remaining elements
a, *b = nums
print(a, b)

# Result
1 [2, 3, 4, 5]
## using tuple
## here first element will assign to a and last element to c
a, *b, c = (1, 2, 3, 4, 5)
print(a, b, c)

print("--------------------------")

## using sets
a, *b, c = {1, 4, 9, 16, 25}
print(a, b, c)

## Result
1 [2, 3, 4] 5
--------------------------
1 [4, 9, 16] 25

1.1 Combining Different Iterables​

## combining a tuple, list, set
nums = [1, 2, 3]
nums2 = (4, 5, 6)
nums3 = {7, 8, 9}

## we convert the combined elements into any iterable we want
## here i am converting into a list
_list = [*nums, *nums2, *nums3]
_tuple = (*nums, *nums2, *nums3)
_set = {*nums, *nums2, *nums3}

## Result
[1, 2, 3, 4, 5, 6, 8, 9, 7]
(1, 2, 3, 4, 5, 6, 8, 9, 7)
{1, 2, 3, 4, 5, 6, 7, 8, 9}

1.2 Nested Unpacking​

languages = ["Python", "HTML", "CSS", "JS"]

## unpacking
[[first_letter, *remaining], *other] = languages
print(first_letter, remaining, other)

## Result
P ['y', 't', 'h', 'o', 'n'] ['HTML', 'CSS', 'JS']

2. Unpacking Using ** for dictionary literals​

event_info = {'year': '2020', 'month': '01', 'day': '7', 'group': 'Python Meetup'}
new_info = {**event_info, 'day': "14"}
new_info

# {'year': '2020', 'month': '01', 'day': '14', 'group': 'Python Meetup'}

3. Asterisks In Function​

3.1. Unpacking In Functions​

The * operator is used to call a function by unpacking an iterable. Let's say we have a list and have to pass all the elements of it to the print() separately. What will you do? I think you are thinking of a loop. But, * makes this very easy for us.

Just pass the iterable as *iterable_name. It unpacks the iterable and passes all the elements separately.

nums = [i for i in range(1, 6)]
## passsing list using the *
print(*nums)
>> 1 2 3 4 5


nums = (i for i in range(1, 6))
## passsing tuple using the *
print(*nums, sep = ", ")
>> 1, 2, 3, 4, 5

3.2. Packing Elements​

# *num denotes it can take an arbitrary number of **non-named variables**
def average(*nums):
    return sum(nums) / len(nums)
print(average(1, 2, 3, 4, 5))
>> 3.0
# **properties denotes it can take an arbitrary number of **named variables**
def _object(name, **properties):
    print(name, properties)

_object("Car", color="Red", cost=999999, company="Ferrari")
>> Car {'ceo': 'Louis', 'color': 'Red', 'cost': 999999, 'company': 'Ferrari'}

4. Keyword-Only Arguments With Positional Arguments​

  • Arguments with the name are called keyword arguments.
  • Other arguments are called positional arguments.
# name is a positional argument, color and cost are keyword arguments
def sample(car, color = None, cost = None):
    print("Car:-{} Color:-{}, Cost:-{}".format(car, color, cost))

# The order of keyword arguments is not essential if we call them using the names defined in the function.
sample("Ferrari", color = "Green")
>> Car:-Ferrari Color:-Green, Cost:-None
# We have to use the _list and default keywords while calling the function as they come after the *items. 
def keyword_only(*items, _list, default = False):
    print(items)
    print(_list)
    print(default)

nums = [i ** 2 for i in range(1, 6)]
## calling the function
keyword_only(1, 2, 3, 4, 5, _list = nums, default = True)

>>>
(1, 2, 3, 4, 5)
[1, 4, 9, 16, 25]
True

5. Keyword-Only Arguments Without Positional Arguments​

def _sample(*, name):
    print(name)

## calling the function using keyword 'name'
_sample(name = "Datacamp")
>>> Datacamp

## calling the function without using keyword 'name'
_sample("Datacamp")
>>>
---------------------------------------------------------------------------

TypeError Traceback (most recent call last)

<ipython-input-12-fe0d3718b56c> in <module>()
      1 ## calling the function without using keyword 'name'
      2 ## we will get a TypeError
----> 3 samp("Datacamp")


TypeError: samp() takes 0 positional arguments but 1 was given
It's clear that the _sample() func
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