Lets say I have a string that consists of x unknown chars. How could I get char nr. 13 or char nr. x-14?
7 Answers
First make sure the required number is a valid index for the string from beginning or end , then you can simply use array subscript notation. use len(s) to get string length
>>> s = "python" >>> s[3] 'h' >>> s[6] Traceback (most recent call last): File "<stdin>", line 1, in <module> IndexError: string index out of range >>> s[0] 'p' >>> s[-1] 'n' >>> s[-6] 'p' >>> s[-7] Traceback (most recent call last): File "<stdin>", line 1, in <module> IndexError: string index out of range >>> 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 = '한국中国にっぽん' 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 = '한국中国にっぽん' s = s.decode('utf-8') for i in range(len(s)): print s[i] Python.org has an excellent section on strings here. Scroll down to where it says "slice notation".
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 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
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' 
