If <not number>?

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Join Date: Jan 2008

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If <not number>?

Jul 11th, 2008

I need an if statement that will run if the value is not a number.
I am unsure how to do this in python I have tried looking around and I can't seem to find what I need.

If Input is not <a number>

Also if you can help me restrict this to positive numbers that would be appreciated as well.

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Re: If <not number>?

Jul 11th, 2008

There are a few possibilities I can think of, but probably the most straight forward:

 Help with Code Tags 
 python Syntax (Toggle Plain Text) 
>>> li = [ 1, 2.3, 4e-5, 'hey!' ]
>>> for item in li:
...     test = str(item)
...     if test == item:
...         print item, 'String!'
...     else:
...         print item, 'Not String!'
...     
1 Not String!
2.3 Not String!
4e-005 Not String!
hey! String!
>>> 
>>> li = [ 1, 2.3, 4e-5, 'hey!' ]
>>> for item in li:
...     test = str(item)
...     if test == item:
...         print item, 'String!'
...     else:
...         print item, 'Not String!'
...     
1 Not String!
2.3 Not String!
4e-005 Not String!
hey! String!
>>> 

Now when you say restrict this to positive numbers, do you mean:
If Input is not <a positive number>:
perform action

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Join Date: Jan 2008

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Re: If <not number>?

Jul 11th, 2008

yep exactly, if they input a negative number it will return differentiate that form a positive number.
Also thanks alot for what you have given me.

Last edited by linkrulesx10 : Jul 11th, 2008 at 11:49 am.

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Re: If <not number>?

Jul 11th, 2008

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Originally Posted by linkrulesx10

yep exactly, if they input a negative number it will return differentiate that form a positive number.
Also thanks alot for what you have given me.

 Help with Code Tags 
 python Syntax (Toggle Plain Text) 
>>> li = [ 1, -2, 2.3, 't', -5.3e5, -0.1, 4e-5, 'hey!' ]
>>> for item in li:
...     test = str(item)
...     if test == item:
...         print item, 'String!'
...     else:
...         if item < 0:
...             print item, 'Not string... negative!'
...         else:
...             print item, 'Not string... positive!'
...     
1 Not string... positive!
-2 Not string... negative!
2.3 Not string... positive!
t String!
-530000.0 Not string... negative!
-0.1 Not string... negative!
4e-005 Not string... positive!
hey! String!
>>> 
>>> li = [ 1, -2, 2.3, 't', -5.3e5, -0.1, 4e-5, 'hey!' ]
>>> for item in li:
...     test = str(item)
...     if test == item:
...         print item, 'String!'
...     else:
...         if item < 0:
...             print item, 'Not string... negative!'
...         else:
...             print item, 'Not string... positive!'
...     
1 Not string... positive!
-2 Not string... negative!
2.3 Not string... positive!
t String!
-530000.0 Not string... negative!
-0.1 Not string... negative!
4e-005 Not string... positive!
hey! String!
>>> 

Simply check if the number is less than zero to determine if it is negative.
Just remember to do this only after you've verified that the item is not a string or else you will run into some strange results.

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Re: If <not number>?

Jul 12th, 2008

This is just jlm699's code wrapped into a function ...

 Help with Code Tags 
 python Syntax (Toggle Plain Text) 
def isPositiveNumber(n):
    """returns True if n is a positive number, else returns False"""
    # check if n is a string
    q = str(n)
    if q == n:
        return False
    if n > 0:
        return True
    else:
        return False
 
# test the function
if __name__ == '__main__':
    mylist = li = [ 1, -2, 2.3, 't', -5.3e5, -0.1, 4e-5, 'hey!' ]
    for item in mylist:
        print item, isPositiveNumber(item)
def isPositiveNumber(n):
    """returns True if n is a positive number, else returns False"""
    # check if n is a string
    q = str(n)
    if q == n:
        return False
    if n > 0:
        return True
    else:
        return False

# test the function
if __name__ == '__main__':
    mylist = li = [ 1, -2, 2.3, 't', -5.3e5, -0.1, 4e-5, 'hey!' ]
    for item in mylist:
        print item, isPositiveNumber(item)

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Re: If <not number>?

Jul 12th, 2008

If you are using raw_input or the variable is already a string, then try isdigit(). This of course assumes that you aren't using floating point numbers. If you are then you will have to use a try/except converting the string to a float.

Help with Code Tags

(Toggle Plain Text)

get_num=raw_input("Enter a number ")
print get_num,
if get_num.isdigit():
   if int(get_num) > 0:
      print "is integer and is positive"
   else:
      print "is integer and is NOT positive"
## this will never execute since a minus sign, "-", is not a digit
else:
   print "is NOT a number"

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Re: If <not number>?

Jul 12th, 2008

Or this:

 Help with Code Tags 
 Python Syntax (Toggle Plain Text) 
try:
    val = int(item)
    if val > 0:
        do stuff for positive numbers
    elif val < 0:
        do stuff for negative numbers
    else:   # don't omit zero!
        do stuff for zero
except:
    pass
try:
    val = int(item)
    if val > 0:
        do stuff for positive numbers
    elif val < 0:
        do stuff for negative numbers
    else:   # don't omit zero!
        do stuff for zero
except:
    pass

If you want to allow floating point numbers, you can change the int() to float()

Jeff

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Re: If <not number>?

Jul 14th, 2008

 Help with Code Tags 
 python Syntax (Toggle Plain Text) 
def valid(x):
    # check if n is a string
    q = str(x)
    if q == x:
        print "Error, Not valid input"
        break
    else:
 
        if x > 0:
            print ""
        else:
            print "Error, Not valid input"
            break
def valid(x):
    # check if n is a string
    q = str(x)
    if q == x:
        print "Error, Not valid input"
        break
    else:
    
        if x > 0:
            print ""
        else:
            print "Error, Not valid input"
            break

I am using this to break a loop if there is invalid input.

Thank you for all your help, it solved quite a big problem for me

Last edited by linkrulesx10 : Jul 14th, 2008 at 5:14 am.

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Re: If <not number>?

Jul 14th, 2008

Ok, Modules Idea is not working as it sets that as something different outside of the loop it is currently in so any variables (and break commands) seem to not work...
Is there a way I can make a variable global or somehow allow a module to break a loop.