How do I check if input has been entered?
For example (python2)
x = str(raw_input('Message>> '))
or (python3)
y = input('Number>> ')
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1The input function won't return until something has been entered. Do you mean how to check if the entered input is empty?Mark Ransom– Mark Ransom2012-03-28 19:09:01 +00:00Commented Mar 28, 2012 at 19:09
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2 Answers
You know if nothing was entered for the second one because it will raise a SyntaxError. You can catch the error like this:
try:
y=input('Number>> ')
except SyntaxError:
y = None
then test
# not just 'if y:' because 0 evaluates to False!
if y is None:
or, preferably, use raw_input:
try:
y = int(raw_input('Number>> '))
except ValueError:
print "That wasn't a number!"
For the first one, x will be an empty string if nothing is entered. The call to str is unnecessary -- raw_input already returns a string. Empty strings can be tested for explicitly:
if x == '':
or implicitly:
if x:
because the only False string is an empty string.
4 Comments
agf
@hochl If just spaces aren't a valid message :)
IT Ninja
Perfect! Thank you so much for your answer agf and hochl. :)
Dennis
What about
if not x: or if len(x) < 1: as alternatives to if x == '':, or are those considered bad practice?agf
@Dennis See the last code in my post. I do mention using just
if x: to test emptyness.This also work too
y = input('Number>> ')
while not y:
y = input('Number>> ')
1 Comment
TheHaloDeveloper
Simple, self-explanatory 3 line answers are much more preferred. Thanks :)