python 3.8 version enhasment¶

The 3.8 version new features¶

Warlous Operator
Postional only Parameters
Fstring Support
iSqrt function
continue with finally
reversed dictionary
syntax warning

We can use = symbol f-string for self documentating expressions and it is useful for debugging purposes.

x = 10
y = 10
print(f'{x = }')  # => print(f'x = {x}')
print(f'{y = }')  # => print(f'y = {y}')

We can also use walrus operator (:=) inside f-string:

import math

half_radious = 10

print(f'The Area of circle with radius {(r := 2 * half_radious)} is {math.pi ** r*r }')

Note: () -> This is important in walrous operator in this example other wise we will get error.

print(f'The Area of circle with radius {r := 2 * half_radious} is {math.pi ** r*r }')

f - string can in python 3.6 version but = and := operator are allowed inside f-string in python 3.8 version
% -> formating and str.formate() Not Recommanded.

f string¶

has performance
concise
less verbose
more readable

class Student:
    def __init__(self, name, rollno, marks):
        self.name = name
        self.rollno = rollno
        self.marks = marks
    def __str__(self):
        return f'Name: {self.name}, RollNo: {self.rollno}, Marks: {self.marks}'

    def __repr__(self):
        return f'Student Name: {self.name}, Student RollNo: {self.rollno}, Student Marks: {self.marks}'

s = Student('ashish',101,80)
print('Information-------> {}'.format(s))
print(f'Information-------> {s}')
print(f'Information-------> {s!r}')

Expression inside f-string¶

We can pass expression inside f-string and those expressions will be evaluated at runtime

print({8*8})

How to use curly braces inside f-string¶

{ => replacement operator
{{=> it is simple of '{'

print(f'{{ is special symbol ')
print(f'{{{ is special symbol ')

New Syntax Warning in python 3.8 version¶

In python warning are Exception
Python has a syntaxWarning that can warn about doubtful syntax,that is typically not syntaxerror

BaseException
    └── Exception
        └── Warning
            └── SyntaxWarning

is and is not operators are used for numbers and strings.
While creating larger collections, we may miss some elements.

is and is not operators for numbers and strings¶

is operator vs == operator

is operator meant for reference comparsion
== operator meant for content comparsion

l1 = [10,20,30,40]
l2 = [10,20,30,40]
print(l1 is l2)
print(l1 == l2)

A new SyntaxWarning added extraa in 3.8 version which will be raised if we use is and is not operator for number and string literals.
It is highly recommended to use == operator instead of is for literal comparsion.
While creating large collections, we may miss ',' to alert this, a new syntax warning was added to Python 3.8.

print(6 is 6)
print('a' is ' a')

python 3.8 = > oct 14 2019
python 3.9 = > oct 5 2020

More flexibility to programmer with new features

1. The Warlus operator:(sea hourse)¶

Syntax :=

This operator released as the part of PEP 577
PEP => Python Enhancement Proposals
To assign values to the variable as the oasrt of expression itself

# Assignment Expression
num = [10,20,30,40,50,60]
length = len(num)

if length > 3:
    print('List conatins more than 3 element')
    print('The length of the list is', length)

num = [10,20,30,40,50,60]

if (n:=len(num)) > 3:
    print('List conatins more than 3 element')
    print('The length of the list is', length)

# Example 2
heriones = []

herion = input('Enter your Favourit Herione ')

while herion != 'done':
    heriones.append(herion)
    herion = input('Enter your Favourit Herione ')

print(heriones)

heriones = []

while (herion := input('Enter your Favourit Herione '))!= 'done':
    heriones.append(herion)

print(heriones)

# Read data line by line from abc.txt file and print to the console.
# FileNotFoundError

f = open('abc.txt')
line = f.readline()

while line != '':
    print(line, end='')
    line = f.readline()

f.close()

The Walrus Operator is a new addition to Python 3.8 and higher. In this article, weâ€™re going to discuss the Walrus operator and explain it with an example.

Introduction¶

Walrus Operator allows you to assign a value to a variable within an expression. This can be useful when you need to use a value multiple times in a loop, but donâ€™t want to repeat the...

numbers = [1, 2, 3, 4, 5]
while (n := len(numbers)) > 0:
    print(numbers.pop())

f = open('abc.txt')

while (line := f.readline()) != '':
    print(line, end='')

f.close()

The main advantage of warlous Operator¶

It won't do any new thing
It just reduce length of code and readablity will be imporoved

2. Postional-only parameter¶

python 3.8 version PEP 570

Postional argument
- order and number both are implemented
keyword argument
- By keyword (parameter name) (a=10, b=20), (b=20, a=10)
- The number of argument must be match order is notimportant
default arguments:
- def sum(a=0,b=0) argument with default value
- `def sum(a=0,b) -- x after a arument, we cannot take non-default argument
varable length argument and all value will be converted into touple
- def f(*args) -print(args)
- *args and **kwargs

def calc(a,b): # a,b parameter
    print(a+b)
    print(a-b)
    print(a*b)

calc(10,20) # arguments
# Interchangable we can use

Function types¶

Postional arguments
Keyword arguments
default arguments
varable legth argument

calc(20,30) # Postional argument

1. The number of argument must be match and order¶

Keyword only parameters (3.0 -Version)¶

After *, all parameter will become keyword only paramter
At the time of calling we should pass values by keyword only

def f1(*,a,b):
    print(a,b)

f1(a=10, b=20) # valid
f1(10, 20) # TypeError: f1() takes 0 postional arguments but 2 were given
f1(10, b=20)  # TypeError: f1() takes 0 positional arguments but 1 positional argument (and 1 keyword-only argument) were given

def f(a,*,b,c):
    """
    # For a we can pass value either by postional or keyword But
      for b,c compulosry we should use keyword
    """
    print(a,b,c)

def f2(*,a=10,b,c): # correct
    ...
def f3(a=10,b,c,*): # error SyntaxError: non-default argument follows default argument
    ...

Positional only arguments: (3.8)¶

We should pass values by postional only arguments
/ => Forword slash
All paramters vefore /, will bwcome postional only paramters

def f3(a,b,/):
    print(a,b)

f3(10,20)
f3(a=10,b=20)

Python 3.8 version as the past PEP 570¶

a and b are postional only parameteers
c and d are postional or keyword paramters
e and f are keyword only paramters

def f4(a,b,/,c,d,*,e,f):
    print(a,b,c,d,e,f)

f4(10,20,30,d=40,e=50,f=60)
f4(10,b=20,c=30,d=40,e=50,f=60)
f4(10,20,30,40,50,f=60)

f4(postional args,postional or keyword,keyword only args)¶

Problem without postional only argument¶

case - 1:

Without effecting client, we cannont change parameter name based on our requirment

def display(name, arg, roll):
    print(name, arg, roll)

display('Ravi',14,101)
display(name = 'Ravi', age = 14, roll = 101)
display('Ravi', 14, roll = 101)

If arguments are postional only, then we can change variable names¶

def display(name, arg, roll,/):
    print(name, arg, roll)

python 3.8 version enhasment¶

The 3.8 version new features¶