Python Strings

Python has a built-in string class named "str" with many handy features (there is an older module named "string" which you should not use). String literals can be enclosed by either double or single quotes, although single quotes are more commonly used.

Python strings are "immutable", which means they cannot be changed after they are created (Java strings also use this immutable style).

  s = 'hi'
  print(s[1])          ## i
  print(len(s))        ## 2
  print(s + ' there')  ## hi there

String Methods

• s.lower(), s.upper() -- returns the lowercase or uppercase version of the string

• s.strip() -- returns a string with whitespace removed from the start and end

• s.isalpha()/s.isdigit()/s.isspace()... -- tests if all the string chars are in the various character classes

• s.startswith('other'), s.endswith('other') -- tests if the string starts or ends with the given other string

• s.find('other') -- searches for the given other string (not a regular expression) within s, and returns the first index where it begins or -1 if not found

• s.replace('old', 'new') -- returns a string where all occurrences of 'old' have been replaced by 'new'

• s.split('delim') -- returns a list of substrings separated by the given delimiter. The delimiter is not a regular expression; it's just text. 'aaa,bbb,ccc'.split(',') -> ['aaa', 'bbb', 'ccc']. As a convenient special case, s.split() (with no arguments) splits on all whitespace chars.

• s.join(list) -- opposite of split(), joins the elements in the given list together using the string as the delimiter. e.g. '---'.join(['aaa', 'bbb', 'ccc']) -> aaa---bbb---ccc

String Slices
The "slice" syntax is a handy way to refer to sub-parts of sequences -- typically strings and lists. The slice s[start:end] is the elements beginning at start and extending up to but not including end. Suppose we have s = "Hello"

The string 'hello' with letter indexes 0 1 2 3 4