Python Newbie 3

1. The walrus operator

Walrus operator is the coolest feature that was added in the Python 3.8 update python codes.

start = input("Do you want to start(y/n)?")
print(start == "y")


# double parentheses here 
# using parentheses with the walrus operator is encouraged
print((start := input("Do you want to start(y/n)?")) == "y")

# With parentheses
if (sum := 10 + 5) > 10:
    print(sum) #return 15 
    
# Without parentheses 
if sum := 10 + 5 > 10:
    print(sum) #return True

a = [1, 2, 3, 4]
if (n := len(a)) > 3:
    print(f"List is too long ({n} elements, expected <= 3)")

2. Positional-only parameters

There is a new function parameter syntax / to indicate that some function parameters must be specified positionally and cannot be used as keyword arguments.

def name(positional_only_parameters, /, positional_or_keyword_parameters, *, keyword_only_parameters):

>>> def f(a,b,/,**kwargs):
...   print(a,b,kwargs)
...
>>> f(10,20,a=1,b=2,c=3)
10 20 {'a': 1, 'b': 2, 'c': 3}

def do_nothing(a, b, /):
  print(a, b)

>>> do_nothing(1, 2)
1, 2

>>> do_nothing(a=1, b=2)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: do_nothing() takes no keyword arguments