Require user input until is correct [duplicate] - python-3.x

Question

This question already has answers here:
Asking the user for input until they give a valid response
(22 answers)
Closed 2 years ago.
What is the best way of repeatedly asking for the user for correct input?
For example I'd like to continue checking if the a value is an int or not and when it is finally say ok you picked number.
I'm stuck here:
try:
a = int(input())
except:
print("incorrect pick a number and try again")
#Somewhere here
print("Ok thanks you finally picked a number")

Answer 1

The only exception you want to catch is the ValueError raised by int should it not be able to convert its argument to an integer. The try statement will be in a loop that you will explicitly break out of if you don't get an exception.
while True:
response = input()
try:
a = int(response)
except ValueError:
print("incorrect pick a number and try again")
else:
print("Ok thanks you finally picked a number")
break

Answer 2

if you want/must mantain this code, i think the unique way is using a loop.
while True:
try:
a = int(input('Insert a number:'))
print ('Your number is {}'.format(a))
break
except ValueError:
print("incorrect pick a number and try again")
So if the user inserts an integer, the code prints number and break the loop else repeats the request.
I hope it's useful for you!

Answer 3

You can do it like this:
a = None
while type(a) != int:
try:
a = int(input())
except:
print("incorrect pick a number and try again")
print("Ok thanks you finally picked a number")
Essentially:
Create a variable with NoneType so when you first run the program it can access the while loop because the conditions meats.
Loop until the type of that variable is not int.
Request the user input and try to cast as integer, if it fails print an error and try again.
When the input is of integer type it exit the loop and print the final message.
You can use type() or isinstance() to check, but as suggested by #chepner avoid the usage of type because it simply returns the type of an object whereas, isinstance() returns true if the object argument is an instance of the classinfo argument, or of a (direct, indirect or virtual) subclass thereof.
To help you understand:
class foo:
pass
class bar(foo):
pass
isinstance(foo(), foo) # returns True
type(foo()) == foo # returns True
isinstance(bar(), foo) # returns True
type(bar()) == foo # returns False,and this probably won't be what you want.
In the case you want to use isinstance() the code will result as:
a = None
while not isinstance(a, int):
try:
a = int(input())
except:
print("incorrect pick a number and try again")
print("Ok thanks you finally picked a number")
As pointed out by #L3viathan you can also do:
a = None
while a is None:
try:
a = int(input())
except:
print("incorrect pick a number and try again")
print("Ok thanks you finally picked a number")
In this case you loop until a get a value, that will be done only if the exception is not thrown.

Answer 4

while True:
try:
number=int(input("Enter a number: "))
except:
print("incorrect pick a number and try again")
else:
print("ok Thanks you finally picked a number ")
break