Everything * Can Be Used For In Python (Aside From Basic Math)
1) *args in Function Parameters
We can add *args in our function parameters to enable our function to take in any number of positional arguments. The * before args indicates that it will collect any number of positional arguments into a single variable. Inside the function, args is treated as a tuple.
def hello(*args):
print(args)
hello()
hello(1)
hello(1, 2)
hello(1, 2, 3)
def hello(a, b, *args):
print(args)
hello(1, 2)
hello(1, 2, 3)
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2) **kwargs in Function Parameters
Using ** instead of * allows us to take in any number of keyword arguments. Inside the function, kargs is treated as a dictionary, which stores key-value pairs.
def hello(**kargs):
print(kargs)
hello()
hello(a=1)
hello(a=1, b=2)
def hello(a, b, **kwargs):
print(kwargs)
hello(a=1, b=2)
hello(a=1, b=2, c=3)
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3) *args in Function Arguments
We can also use * to unpack an iterable into our function arguments.
L = [1, 2]
print(*L)
D = {1:'a', 2:'b'}
print(*D)
def hi(a, b, c):
print(f"{a=} {b=} {c=}")
hi(1, 2, 3)
L = [4, 5, 6]
hi(*L)
def hi(a, b, c):
print(f"{a=} {b=} {c=}")
hi(1, 2, 3)
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4) **kwargs in Function Arguments
If we use ** instead of *, we can do the same with dictionaries. Here, hi(**mydict) is the same as hi(a=4, b=5, c=6)
def hi(a, b, c):
print(f"{a=}, {b=}, {c=}")
hi(a=4, b=5, c=6)
D = {'a':4, 'b':5, 'c':6}
hi(**D)
Similarly, we can also combine normal keyword arguments with **mydict as long as we pass all required keyword arguments into our function.
def hi(a, b, c):
print(f"{a=}, {b=}, {c=}")
D = {'a':4, 'b':5, 'c':6}
hi(**D)
D = {'b':5, 'c':6}
hi(a=4, **D)
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5) Any parameter after * must be a keyword argument.
* is not placed before any parameter — this means that any parameter defined after * must be a keyword argument. In this case, c & d come after *, so c & d can only be keyword arguments. a & b can be positional or keyword arguments, but c & d must be keyword arguments.
def hello(a, b, *, c, d):
print(a, b, c, d)
hello(1, 2, c=3, d=4)
hello(a=1, b=2, c=3, d=4)
If we replace * alone with a / alone, this means that any function parameter defined before the / must be a positional argument.
def hello(a, b, /, c, d):
print(a, b, c, d)
hello(1, 2, c=3, d=4)
hello(1, 2, 3, 4)
We can combine these to force additional restrictions on our function parameters.
def hola(a, b, /, c, d, *, e, f):
print(a, b, c, d, e, f)
hola(1, 2, 3, d=4, e=5, f=6)
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6) *args in tuple unpacking
We can use tuple unpacking to elegantly assign multiple variables at once.
person = ['bob', 'M', 20]
name, gender, age = person
print(name, gender, age)
We can combine tuple unpacking with * if we have unused variables. If we have many more fields in person, but we only need the first 2 for now — we can use *others to assign everything else to the variable others.
person = ['bob', 'M', 20, 1.75, 70, 'black']
name, gender, *others = person
print(name, gender)
print(others)
We can switch the position of the variable with * too — in this example, we only need the first and last value, so we put *others in the middle.
person = ['bob', 'M', 20, 1.75, 70, 'black']
name, *others, hair = person
print(name, hair)
print(others)
In this example, we only need the last 2 values, so we can put *others at the front.
*others, weight, hair = person
print(weight)
print(hair)
print(others)
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7) Using * when combining iterables
We can also use * to combine iterables. Here, we combine 2 lists a & b by unpacking them into a list c.
a = [1, 2]
b = [3, 4]
c = [*a, *b]
print(c)
d = [[*a], [*b]]
print(d)
We can combine this technique with normal values like this:
a = [1, 2]
b = [3, 4]
c = [-1, 0, *a, *b, 5, 6]
print(c)
8) ** in combining dictionaries
** works for key-value mappings the same way * works for individual values. We can use ** to unpack dictionaries into other dictionaries in order to combine them.
x = {'a':1, 'b':2}
y = {'c':3, 'd':4}
z = {**x, **y}
print(z)
z = {**x, **y, 'e':5}
print(z)
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9) Importing everything from a module
We can also use from modulename import * to tell Python that we want to import everything that can be imported from some module.
from random import *
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