String Indexing

We sometimes need to access individual characters in a string. The characters in a string can be located using their index value, which represents their position in the string. Enclosing the index in square brackets will select a single character from a string:

[index number]

To get a character at position i in string str, use square brackets str[i].

• characters are indexed from left to right, starting from the position 0, not 1!
• indexing: the positions are also named from right to left using negative numbers, where -1 is the rightmost index and decreases by one as you move left.
• blank spaces are also considered characters.

Slicing Strings

str[start: end: step] returns a segment, or slice, of the string str. It selects the part of the string from indices start to index end (excluding the number end itself), separating the values by step. The step is 1 by default if you do not include it.

food = 'blueberry muffin'
m = food[2]
t = food[-2]
print (m, t)         # u i

n = food[4:9]
print(n)         # berry (slice from indices 4 to 9, excluding 9)

r = food[4:]
print(r)         # berry muffin (slice from index 4 to the end)

s = food[:4]  
print(s)         # blue (slice from the beginning to index 4)

To understand how slicing works, think of an index as a pointer between each character in a string:

 +---+---+---+---+---+---+
 | P | y | t | h | o | n |
 +---+---+---+---+---+---+
 0   1   2   3   4   5   6
-6  -5  -4  -3  -2  -1   0

0 is before the first element but also after the last element, as if the string wraps around. [start:end] includes everything between the two indices.