Error in input: Python

Question

I have an input with newline between each string. The end will be noted by a number between 1 to 5:

Input: Ha

Ha

Hee

Ho

5

I need to accept this as list of strings in python where my list would contain: ['Ha', 'Ha', 'Hee', 'Hee', 'Ho']

After a lot of googling, I tried the following code:

lines = []

sentinel = range(6)

for i in iter(raw_input, [str(s) for s in sentinel]):
    if i=='':
        continue
    else:
        lines.append(i)

print lines

I don't know why but it goes into an infinite loop.

Please help me out!

What's the number at the end of the input for?

Kevin
– Kevin

2014-09-19 00:21:40 +00:00
Commented Sep 19, 2014 at 0:21 — Kevin
– Kevin, Commented Sep 19, 2014 at 0:21

FatalError · Accepted Answer · 2014-09-19 00:36:17Z

The issue is with the way iter() interpets the sentinel. It's a single value that indicates the end of iteration. For your sentinel to be hit, raw_input() would actually have to return an identical list, which can never happen (since of course it returns a str).

If you wrap things up a bit, you can make it work:

sentinel = range(6)

def anything_but(values):
    values = map(str, values)
    def inner():
        i = raw_input()
        if i in values:
            return None
        return i
    return inner

lines = []
for i in iter(anything_but(sentinel), None):
    lines.append(i)

print lines

In this case, None is the sentinel value which will be returned if a number 0-5 is entered. As an aside, if you wanted 1-5 as you mentioned you should use range(1, 6) instead.

However, you're probably better served doing it with a generator:

sentinel = range(6)

def anything_but(values):
    values = map(str, values)
    i = raw_input()
    while i not in values:
        yield i
        i = raw_input()

lines = []
for i in anything_but(sentinel):
    lines.append(i)

print lines

Padraic Cunningham · Accepted Answer · 2014-09-19 00:28:48Z

0

You can just use a while loop:

inp = raw_input()
while inp not in {"1","2","3","4","5"}:
    if not inp:
       continue
    else:
        lines.append(inp)
    inp = raw_input()
print lines

Using the inputs in your question outputs:

['Ha', 'Ha', 'Hee', 'Hee', 'Ho']

edited Sep 19, 2014 at 0:28

answered Sep 19, 2014 at 0:23

Padraic Cunningham

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