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up vote 2 down vote favorite

Very basic question. We have the code:

a = input("how old are you")

if a == string:
    do this

if a == integer (a != string):  
    do that

Obviously it doesn't work that way. But what is the easiest way to do this. Thanks for any answers in advance.

We could also say:

if string in a:
    do this
share|improve this question
 
I'm not quite sure what you're asking. What do you want? –  feralin Jul 3 at 16:44
 
"But what is the easiest way to do this".. Do what? –  arshajii Jul 3 at 16:44
2  
It's important to note that input is always going to return a string. What you seem to be looking for is a way to detect whether that string contains digits. Make sure you understand the distinction. –  acjohnson55 Jul 3 at 16:48
 
I'm sorry if didn't ask the question very well. Ashwini Chaudhary's answer was perfect. That's all I needed. I was just getting an error in my app everytime the user inputted a letter rather than a number so I wanted the input box to stay in a loop, which broke if the input was an integer. Sorry if the question was asked badly. –  Dennis Callanan Jul 3 at 16:56

3 Answers

up vote 8 down vote accepted

You can use str.isdigit and str.isalpha:

if a.isalpha():
   #do something
elif a.isdigit():
   #do something

help on str.isdigit:

>>> print str.isdigit.__doc__
S.isdigit() -> bool

Return True if all characters in S are digits
and there is at least one character in S, False otherwise.

help on str.isalpha:

>>> print str.isalpha.__doc__
S.isalpha() -> bool

Return True if all characters in S are alphabetic
and there is at least one character in S, False otherwise.
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up vote 2 down vote

You can use a.isalpha(), a.isdigit(), a.isalnum() to check if a is composed of letters, numbers, or a combination of numbers and letters, respectively.

if a.isalpha(): # a is made up of only letters
    do this

if a.isdigit(): # a is made up of only numbers
    do this

if a.isalnum(): # a is made up numbers and letters
    do this

The Python docs will tell you in more detail the methods you can call on strings.

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4  
input will always be a string –  computmaxer Jul 3 at 16:45
 
Yeah, you are right. –  jh314 Jul 3 at 16:56
up vote 0 down vote

Seen that you use input() in tour example you should know that input always give you a string. And you need to cast it to the correct type, EG: Int, or Float.

def isint(input):
    return input.isdigit()

def isfloat(input):
    try: 
        return float(input) != None;
    except ValueError: 
        return False;

def isstr(input):
    if not isint(input) and not isfloat(input):
        return True
    return False

print isint("3.14")
print isfloat("3.14")
print isstr("3.14")
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