This should further clarify the points:
a = int(raw_input('Enter the index'))
str1 = 'Example'
leng = len(str1)
if (a < (len-1)) and (a > (-len)):
print str1[a]
else:
print('Index overflow')
Input 3 Output m
Input -3 Output p
Python.org has an excellent section on strings here. Scroll down to where it says "slice notation".
I think this is more clear than describing it in words
s = 'python'
print(len(s))
6
print(s[5])
'n'
print(s[len(s) - 1])
'n'
print(s[-1])
'n'
Another recommended exersice for understanding lists and indexes:
L = ['a', 'b', 'c']
for index, item in enumerate(L):
print index + '\n' + item
0
a
1
b
2
c
In [1]: x = "anmxcjkwnekmjkldm!^%@(*)#_+@78935014712jksdfs"
In [2]: len(x)
Out[2]: 45
Now, For positive index ranges for x is from 0 to 44 (i.e. length - 1)
In [3]: x[0]
Out[3]: 'a'
In [4]: x[45]
---------------------------------------------------------------------------
IndexError Traceback (most recent call last)
/home/<ipython console> in <module>()
IndexError: string index out of range
In [5]: x[44]
Out[5]: 's'
For Negative index, index ranges from -1 to -45
In [6]: x[-1]
Out[6]: 's'
In [7]: x[-45]
Out[7]: 'a
For negative index, negative [length -1] i.e. the last valid value of positive index will give second list element as the list is read in reverse order,
In [8]: x[-44]
Out[8]: 'n'
Other, index's examples,
In [9]: x[1]
Out[9]: 'n'
In [10]: x[-9]
Out[10]: '7'
Previous answers cover about ASCII character at a certain index.
It is a little bit troublesome to get a Unicode character at a certain index in Python 2.
E.g., with s = '????????' which is <type 'str'>,
__getitem__, e.g., s[i] , does not lead you to where you desire. It will spit out semething like ?. (Many Unicode characters are more than 1 byte but __getitem__ in Python 2 is incremented by 1 byte.)
In this Python 2 case, you can solve the problem by decoding:
s = '????????'
s = s.decode('utf-8')
for i in range(len(s)):
print s[i]
Source: Stackoverflow.com