用户如何在不崩溃的情况下输入str和int？

Question

I am writing a calendar program. If the user enters a negative number for the year it ask them again to enter a positive until they do so. How can I write the piece of code to allow them to enter alpabetical letters by mistake unlimited number of times until they finally under a positive int? And vis versa? If they write a letter then -number then letter?

Having the input set to an int will now allow letters to be enter repeated. But If I take it out then I will never able to inter an int

def func():
    first_year = (input("What year would you like to start?\n"))     #input set to varibale for users desired start yea 

    while type(first_year) == str:
        first_year = int(input("Please enter a number value. What year would you like to start?\n"))

    while first_year < 0:               
        first_year = int(input("Please enter a nonnegative year. What year would you like to start?\n"))        #while loop to make sure year is a valid positive year

    print("You have chosen the year " + str(first_year) + " as your starting year") 

    end_year = int(input("What would you like to print up to?\n"))      #input set to variable for users desired end year

    while end_year < 0:
        end_year = int(input("Please enter a nonnegative year. What year would you like to end with?\n"))

    print("You have chosen the year " + str(end_year) + " as your ending year")   #delete later

    format = input("What date format do you want to print? Ex. with slashes ' 1/1/2000 ' or by printed month 'Januaray, 1, 2000' ? Please enter '-' for slashes or 'print' for printed month." )

Answer 1

input = raw_input("Give a number: ")
try:
    input = int(input)
except ValueError:
    # input is not parsable to string
    do_something()        

Answer 2

I will try to solve your issue partially. You can try using isinstance() something like this.

def func():
    first_year = (input("What year would you like to start?\n"))     #input set to varibale for users desired start yea 
    if isinstance(first_year,(str,)):   ## checks if first_year is of string type
        ## do whatever you want when its string.
    elif isinstance(first_year,(int,)):  ## checks if first_year is of int type
        ## do what you want when its int.
        if first_year >= 0 : ### this checks for negative value
              # go ahead with your program  
        else:
            ## ask the user to put positive values.