[SOLVED] What is the use of '*' in python

Question

Hi! What is the use of '*' in python. Well! I m not talking about the multiplication or wildcard operator. I have seen this was used many time with python lists
For example
ls = [3,5,3,5,35]
print(*ls) #will produce the list without , and []
Also I have heard this was used for unpacking list.

But what are the real used of it. And can u explain each example - including the things i have mentioned above

Answer 1

Let's say your function takes two int arguments:

def f(x, y):
...

Now you have a tuple

t = (5, 7)

If you pass it just like this, you'll get an error - not enough args.

So instead you write:

f(*t)

You tuple is 'unpacked' and becomes two values for the call.

You can also do this for dicts:

d = {'x': 1, 'y': 3}

f(**d)

In this case, the keys of the dict must match the parameter names.

Also you can use this in parameters:

def f(*t, **d):
...

Here you can pass as many args as you want; unnamed ones land in tuple t, named ones in dict d.

And in assignments:

a, *b = (1, 2, 3)

b will become a list (!) with 2 and 3 (because a takes 1 and b gets what's left).

a, *b = (5,)

Here b would become an empty list, because that's what's left - nothing.

Answer 2

Another interesting feature of * is to force the usage of keyword parameters when calling a function:

def foo(a, b, *, c=4, d=2):
return 42

foo(1, 2, 3, 4)
This will result in an error

foo(1, 2, c=3, d=4)
This returns 42 with no issues

every parameter to the right of the * must be used with its corresponding keyword

source: Real Python newsletter
https://www.getdrip.com/deliveries/ksz5js8gfrvfnrstby5n?

Answer 3

Oh HonFu got it thanks

Answer 4

No, it has no relation to pointers.

Answer 5

great answer HonFu. I have used A single * in defining my printf for python, but not the ** yet.

Printf.py

https://code.sololearn.com/cH7fs55oWP8G/?ref=app

Answer 6

Is there a similarity to how * is used here to 'pointers' in C++?

Answer 7

It works like an ES6 spread and rest operator.

Answer 8

" * " is used to multiply the values in python and also in all programming languages.

Answer 9

Basically * represents variable no of positional argument and ** represents variable no of key word argument

Ex

def fun(*args):
for i in args:
print(i)
for j in kwargs:
print(j,kwargs[I])

The function fun can be passed with any number of positional and keyword argument

Ex. fun(1,2,3,4) fun(1,2,3,4,5,6,7,8)

Ex fun(a = 1,b = 2,c = 3) fun(a = 1,b = 2)

Answer 10

Multiplication

Answer 11

Whew, fancy! :)

Answer 12

Let's say your function takes two int arguments:

def f(x, y):
...

Now you have a tuple

t = (5, 7)

If you pass it just like this, you'll get an error - not enough args.

So instead you write:

f(*t)

You tuple is 'unpacked' and becomes two values for the call.

You can also do this for dicts:

d = {'x': 1, 'y': 3}

f(**d)

In this case, the keys of the dict must match the parameter names.

Also you can use this in parameters:

def f(*t, **d):
...

Here you can pass as many args as you want; unnamed ones land in tuple t, named ones in dict d.

And in assignments:

a, *b = (1, 2, 3)

b will become a list (!) with 2 and 3 (because a takes 1 and b gets what's left).

a, *b = (5,)

Here b would become an empty list, because that's what's left - nothing.

Answer 13

it can mean multiply as shown below:
3*5
15

Answer 14

The multiplaction function would be the most basic answer