Strings as sequences

Strings are sequences

We’ve already seen another sequence type: strings. Strings are nothing more than immutable sequences of characters (more accurately sequences of Unicode code points). Since a string is a sequence, we can use index notation to read individual characters from a string. For example:

>>> word = "omphaloskepsis"  # which means "navel gazing"
>>> word[0]
'o' 
>>> word[-1]
's'
>>> word[2]
'p'

We can use in to check whether a substring is within a string. A substring is one or more contiguous characters within a string.

>>> word = "omphaloskepsis" 
>>> "k" in word
True
>>> "halo" in word
True
>>> "chicken" in word
False

We can use min() and max() with strings. When we do, Python will compare characters (Unicode code points) within the string. In the case of min(), Python will return the character with the lowest-valued code point. In the case of max(), Python will return the character with the highest-valued code point.

We can also use len() with strings. This returns the length of the string.

>>> word = "omphaloskepsis"
>>> max(word)
's' 
>>> min(word)
'a'
>>> len(word)
14

Recall that Unicode includes thousands of characters, so these work with more than just letters in the English alphabet.

Comprehension check

1. What is returned by max('headroom')?
2. What is returned by min('frequency')?
3. What is returned by len('toast')?

Copyright © 2023–2025 Clayton Cafiero

No generative AI was used in producing this material. This was written the old-fashioned way.