Python infinite while loop inside a function

Question

No matter what I try I keep getting an infinite loop with this function:

  # Excercise 33 - LPTHW

i = 0 
numbers = []

#Ec 1
#numb = 6
#iplus = 10

def theloop(numb):
        global i
        #i = 0
        #number = []
        while i < numb:
            print "At the top of i is %d" % i
            numbers.append(i)

            i = i + 1
            print "Numbers now: ", numbers
            print "At the bottom i is %d" % i

        print "The numbers: "

        for num in numbers:
            print num

theloop(7)

When I run the script it just keeps printing:

At the top of i is 0
At the top of i is 0
...

Thanks in advance.

Is this exactly the script you're running? Because it works fine for me here. — James Aylett
– James Aylett, Commented Mar 25, 2012 at 1:00
Ran the script in Python 3 (correcting the print syntax). Works fine here. Unless numbers.Append() is doing something strange, what you describe cannot happen. Check your indentation. — Thomas
– Thomas, Commented Mar 25, 2012 at 1:06
LPTHW is a crazy way to learn Python. Look at "Dive into Python 3" or one of the decent tutorials. — Katriel
– Katriel, Commented Mar 25, 2012 at 1:15

DSM · Accepted Answer · 2012-03-25 01:04:52Z

2

Your code works for me as written, but looks to have weird indentation due to use of mixed tabs and spaces. When I read your script using .readlines, you can see this:

 '    def theloop(numb):\n',
 '    \t\tglobal i\n',
 '    \t\t#i = 0\n',
 '            #number = []\n',
 '    \t\twhile i < numb:\n',
 '     \t\t\tprint "At the top of i is %d" % i\n',
 '        \t\tnumbers.append(i)\n',
 '    \n',
 '        \t\ti = i + 1\n',

So I'd recommend switching to four spaces everywhere and having another go. Note the difference in the number of tabs between the print statement and the append/increment statements.

answered Mar 25, 2012 at 1:04

DSM

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1 Comment

jdorfman Over a year ago

Thanks @DSM that was the issue. Also thanks James, Satoru & Thomas for your insight.

Ashwini Chaudhary · Accepted Answer · 2012-03-25 01:13:08Z

1

if you've mixed spaces and tabs then try to run your script like this:

python -tt yourscript.py ##this will raise error if you've mixed spaces and tabs

this is what I am getting after running your script and it's not infinite.

At the top of i is 0
Numbers now:  [0]
At the bottom i is 1
At the top of i is 1
Numbers now:  [0, 1]
At the bottom i is 2
At the top of i is 2
Numbers now:  [0, 1, 2]
At the bottom i is 3
At the top of i is 3
Numbers now:  [0, 1, 2, 3]
At the bottom i is 4
At the top of i is 4
Numbers now:  [0, 1, 2, 3, 4]
At the bottom i is 5
At the top of i is 5
Numbers now:  [0, 1, 2, 3, 4, 5]
At the bottom i is 6
At the top of i is 6
Numbers now:  [0, 1, 2, 3, 4, 5, 6]
At the bottom i is 7
The numbers: 
0
1
2
3
4
5
6

answered Mar 25, 2012 at 1:13

Ashwini Chaudhary

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1 Comment

jdorfman Over a year ago

I will start using -tt great tip.

Jos Kraaijeveld · Accepted Answer · 2012-03-25 01:03:56Z

0

This looks like there is an indenting mistake after the following lines:

   while i < numb:
        print "At the top of i is %d" % i
        numbers.append(i)

Like James said, it works just fine here as you pasted it, so you might want to check if you have the correct indentation level in your actual code.

answered Mar 25, 2012 at 1:03

Jos Kraaijeveld

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