Check if token is an integer?

raskol · 04-05-2008, 04:00 PM

if i use raw_input() and want to see if the input is an integer, is there a way to do this?

jailbait · 04-05-2008, 04:15 PM

What language are you programming in? In general the way that you do this is to read the input into a floating point variable. Then copy the contents of the floating point variable into an integer variable which will truncate the decimal portion of the number. Copy the integer back into a floating point number and compare the two floating point numbers. If they are equal then the original number was an integer.

For example read in 4.3. Copy it to an integer variable where it is truncated to 4. Copy the integer to a floating point variable where it becomes 4.0. Compare 4.0 to 4.3 and the answer is that 4.3 is not an integer.

-------------------
Steve Stites

raskol · 04-05-2008, 04:29 PM

im using python.

the thing is not if its a float or an int.

i want to know if its an int/number or a char.

i found this:
http://python.active-venture.com/lib/module-string.html
This module defines some constants useful for checking character classes and some useful string functions. See the module re for string functions based on regular expressions.

digits
The string '0123456789'.

but dont understand how to use it.

Dan04 · 04-05-2008, 04:37 PM

Code:

value = raw_input()

try:
    value = int(value)
except ValueError:
    print "value is not an integer"

raskol · 04-05-2008, 04:53 PM

Quote:

Originally Posted by Dan04

Code:

value = raw_input()

try:
    value = int(value)
except ValueError:
    print "value is not an integer"

ok ty but is that really a good way to do it?

i mean i could obv test for all if value == '1' or value == '2' etc but that is also kinda bad.

Dan04 · 04-05-2008, 05:04 PM

That's what most Python programmers do. If you're adamant about not using exceptions, you could do (for non-negative values):

Code:

all(char in string.digits for char in value)

But "it's better to ask for forgiveness than permission."

raskol · 04-05-2008, 05:17 PM

Quote:

Originally Posted by Dan04

That's what most Python programmers do. If you're adamant about not using exceptions, you could do (for non-negative values):

Code:

all(char in string.digits for char in value)

But "it's better to ask for forgiveness than permission."

i found this, it works and what was more what i was thinking of:

c=raw_input("yo: ")
if c in '0123456789':
print "integer"
else:
print "char"

however lets say the string is very large(WELL OBV NEVER IN THIS CASE BUT SAy i want see if it is "in" somethign else maybe its very expensive performance-wise?