```
def is_number(s):
    try:
        float(s)
        return True
    except ValueError:
        return False  

flag = True
while flag != False:
    numInput = raw_input("Enter your first number: ")
    if is_number(numInput):
        numInput = float(numInput)
        flag = True
        break
    else:
        print "Error, only numbers are allowed"

```

I do not see the problem.  

Why doesn't it enter a loop?   

Doesn't print anything, just gets stuck.