IndexError: pop index out of range

[Andrew Z]

hello,
going fru some basic examples and can't figureout why the following errors
out. Help is very much appreciated:
<code>
def front_x(words):
# +++your code here+++
print "words passed : ", words
list_xx = []
list_temp = words[:]
print "list_temp -", list_temp
print "words -", words
for idx, val in enumerate(words):
print val, idx
# str_idx = val.find('x',0,2)
if val[0] == 'x':
vl = list_temp.pop(idx)
list_xx.append(vl)

print "appending list_xx", list_xx

list_xx.sort
list_temp.sort
print "words sorted : " + str(words)
print "list_temp sorted : ", list_temp
list_xx.append(words)
print "list_xx" + str(list_xx)
return True

front_x
words passed : ['bbb', 'ccc', 'axx', 'xzz', 'xaa']
list_temp - ['bbb', 'ccc', 'axx', 'xzz', 'xaa']
words - ['bbb', 'ccc', 'axx', 'xzz', 'xaa']
bbb 0
ccc 1
axx 2
xzz 3
appending list_xx ['xzz']
xaa 4
Traceback (most recent call last):
File
"/home/az/work/Python/Google_Course/google-python-exercises/basic/list1.py",
line 119, in <module>
main()
File
"/home/az/work/Python/Google_Course/google-python-exercises/basic/list1.py",
line 100, in main
test(front_x(['bbb', 'ccc', 'axx', 'xzz', 'xaa']),
File
"/home/az/work/Python/Google_Course/google-python-exercises/basic/list1.py",
line 55, in front_x
vl = list_temp.pop(idx)
IndexError: pop index out of range

</code>