* operator : python unpacking

Sadly our memories always seems to fail us. I have come across a code that I was famliar with but wasn't sure what its operation was. It was the * operator.

The * is basically used as a multiplication operator, but when used in front of an argument it works as an unpacking.

My knowledge for other languages are trivial yet, so I'm not sure if there is any other operation overload in other programming languages as well such as C++, Java, Ruby. (May be in Ruby? Considering its similarity with Python?)

Anyway Lets get to the point.

List / Tuple Unpacking

Here's an example.

def getInfo(name, age, address):
	print(name)
	print(age)
	print(address)

x = ('eomiso', 25, 'Seoul')
getInfo(*x)

eomiso
25
Seoul

The with * the list or tuple gets unpacked and works exactly the same as getInfo('eomiso',25,'address') .

Dictionary Unpacking

Let's see an example.

def getInfo(name, age, address):
	print('name: ', name)
	print('age: ', age)
	print('address: ', address)

x = {'name': 'eomiso', 'age': 25, 'address': 'Seoul'}
getInfo(**x)

The result would be as below.

name: eomiso
age: 25
address: Seoul

WARNING

The keys of a dictionary that is used as a argument should be strings.

What happens if you use * instead?

A single asterisk on a dictionary wouldn't cause an error, but you wouldn't get the result you wanted. With singular asterisk you get the keys of the dictionary instead of the values.

Some useful application

1. For placement arguments

def getInfo(*args):
	for arg in args:
		print(arg)

2. For keyword arguments

def getInfo(**kwargs):
	for k,args in kwargs.items(): #don't forget the arguments!
		print(k, ': ', arg, sep=' ')

WARNING

as you can see in print(k, ': ', arg, sep = ' ' ) from above, you can see the placement arguments should come before the keyword arguments. Or else it would throw a syntax Error