elif a=="no": ^ SyntaxError: invalid syntax

Right code:

import codecs
import subprocess
import os

url = "CORONAVIRUS.htm"
while True:
    corona = input("Do you want to know more about Coronavirus-COVID-19?                                                             answer in yes/no format n")
    if corona== "yes":
#Python executes code following the try statement as a “normal” part of the program
        try:
            os.startfile(url)
    #The code that follows the except statement is the program’s response to any exceptions in the preceding try clause.
        except AttributeError:
            try:
                    subprocess.call(['open', url])
            except:
                    print('Could not open URL')
            break
    elif corona=="no":
       print("Have a nice day!")
    else:
        print("Enter either yes/no")

Use this code:

import codecs
import subprocess
import os

while (True):
    corona = input("Do you want to know more about Coronavirus-COVID-19?                                                             answer in yes/no format n")
    if corona== "yes":
        url = "CORONAVIRUS.htm"
#Python executes code following the try statement as a “normal” part of the program
        try:
            os.startfile(url)
        except AttributeError:
            try:
                subprocess.call(['open', URL])
            except:
                print('Could not open URL')
                break
    elif corona=="no":
       print("Have a nice day!")
    else:
        print("Enter either yes/no")

You need to have elif directly after if. You can't have any other lines of codes between an if and the following elifs. You are probably messing up with the indentations in your code. You can edit your code to have try except to be included inside the first if statement and then it will work.

Correct code -

import codecs
import subprocess
import os

while (True):
    corona = input("Do you want to know more about Coronavirus-COVID-19?                                                             answer in yes/no format n")
    if corona== "yes":
        url = "CORONAVIRUS.htm"

        try:
            os.startfile(url)
    #The code that follows the except statement is the program’s response to any exceptions in the preceding try clause.
        except AttributeError:
            try:
                    subprocess.call(['open', url])
            except:
                    print('Could not open URL')
            break
    elif corona=="no":
       print("Have a nice day!")
    else:
        print("Enter either yes/no")