python number guessing question

Question

import sys

print 'Content-Type: text/html' 
print ''

print '<pre>'
# Read the form input which is a single line
guess = -1 
data = sys.stdin.read()
# print data 
if data == []:
    print "Welcome to Josh's number game"
try:
    guess = int(data[data.find('=')+1:]) 
except:
    guess = -1 
print 'Your guess is', guess 
answer = 42 
if guess < answer :
    print 'Your guess is too low' 
if guess == answer:
    print 'Congratulations!' 
if guess > answer :
    print 'Your guess is too high' 
print '</pre>'
print '''<form method="post" action="/"> 
Enter Guess: <input type="text" name="guess"><br> 
<input type="submit">
</form>'''

Right now the program tells you if your guess is too low, too high or right on. I want to add two more messages, one for when someone does not enter any input in the field. And another one for someone who enters invalid input (like a string or something) instead of a number. My field data == [] is meant to show no input in the field, but it doesn't work as I thought. Can you help?

Answer 1

data is a string and will never equal [], which is a list. Try data.strip() == "".

EDIT: It just occurred to me that you probably meant to use sys.stdin.readlines(), which does return a list. But instead of "fixing" this, I strongly recommend you follow @Zack's advice regarding CGI.

Answer 2

sys.stdin.read() will give you an empty string if there's no input, so data == [] should be
data == ''.

The message for invalid input is probably best put inside the except: clause that you already have (you'll need to rearrange your control flow a bit so that becomes exclusive with the number-checking part).

Also, you may find the cgi module useful for what it looks like you're doing.