How do I check an input for an integer in Python?

Question

I used:

day = int(input('Please input the day you were born: e.g 8th=8 21st = 21 : '))
month = int(input('Please input the month you were born: e.g may = 5 december = 12 : '))
year = int(input('Please input the year you were born: e.g 2001 / 1961 : '))

if day == int and month == int and year == int:

But it always even when it's an integer says it's wrong.

By virtue of wrapping your input calls in int(, your type checking becomes useless, because there are only two possibilities: 1) day, month, and year are all integers; or 2) your program crashed with a ValueError within the first 3 lines and the if will never run. — Kevin
– Kevin, Commented Nov 12, 2015 at 20:24
Could you give more detail about what "But it always even when it's an integer says it's wrong."? What exactly is your wrong input and output? — QuestionC
– QuestionC, Commented Nov 12, 2015 at 20:30

Joran Beasley · Accepted Answer · 2015-11-12 20:32:31Z

9

def get_int(p,error_msg="Thats Not An Int!"):
    while True:
         try:
            return int(raw_input(p))
         except (ValueError,TypeError):
            print "ERROR: %s"%error_msg

day = get_int('Please input the day you were born: e.g 8th=8 21st = 21 : ')
#day is guaranteed to be an int

I like to take this and abstract it further

 def force_type(type_class,prompt,error_msg):
     while True:
         try:
            return type_class(prompt)
         except (ValueError,TypeError):
            print error_msg

then it simply becomes

 def get_int(p,err_msg):
     return force_type(int,p,err_msg)
 def get_float(p,err_msg):
     return force_type(float,p,err_msg)
 ...

allthat said if you want to typecheck you should ~not~ use `type(var)` you should use `isinstance(var,int)`

edited Nov 12, 2015 at 20:32

answered Nov 12, 2015 at 20:26

Joran Beasley

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6 Comments

Morgan Thrapp Over a year ago

This isn't OOP enough. Can you make it more OOPy?

Joran Beasley Over a year ago

@MorganThrapp sure def get_int(self,p,err_msg): :P

benjiboi79 Over a year ago

is it possible for you to explain this to me

Adam Smith Over a year ago

@benjiboi79 get_int tries to give you back the user's input (after casting to int). If it fails for whatever reason (like the user types something that isn't a number), it prints an error message and prompts the user to re-input.

Adam Smith Over a year ago

@benjiboi79 the important thing is to realize that after you type int(...), the result WILL BE AN int. You don't have to test for that again. If it fails to convert it to int, it will raise an exception (ValueError or maybe TypeError) and stop execution of your program. By the time your code gets to where you're testing if they're ints, they're guaranteed to be ints.

|

Mr. E · Accepted Answer · 2015-11-12 20:27:50Z

1

To check type you can do:

type(aVar) is aType

Anyway, as Kevin said in a comment you're already wrapping input to int, so either it's actually an int or your program crashed

answered Nov 12, 2015 at 20:27

Mr. E

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Comments

AbtPst · Accepted Answer · 2015-11-12 20:23:15Z

0

try

if type(day) == int and type(month) == int and type(year) == int

answered Nov 12, 2015 at 20:23

AbtPst

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3 Comments

Robᵩ Over a year ago

But that will be a tautology. Given the rest of his code, type(day) will always be int whenever that line of code is executed.

AbtPst Over a year ago

yeah, but i just wanted to show how to access type of variable. dont know why he has declared all three variables as int, in which case there is no need to compare!

AbtPst Over a year ago

you're welcome! please upvote/accept the answer if you found it useful

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allthat said if you want to typecheck you should ~not~ use `type(var)` you should use `isinstance(var,int)`

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allthat said if you want to typecheck you should ~not~ use type(var) you should use isinstance(var,int)

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allthat said if you want to typecheck you should ~not~ use `type(var)` you should use `isinstance(var,int)`