Little Sister's Vocabulary

A str in Python is an immutable sequence of Unicode code points. These could include letters, diacritical marks, positioning characters, numbers, currency symbols, emoji, punctuation, space and line break characters, and more. Being immutable, a str object's value in memory doesn't change; methods that appear to modify a string return a new copy or instance of that str object.

A str literal can be declared via single ' or double " quotes. The escape \ character is available as needed.

>>> single_quoted = 'These allow "double quoting" without "escape" characters.'

>>> double_quoted = "These allow embedded 'single quoting', so you don't have to use an 'escape' character".

>>> escapes = 'If needed, a \'slash\' can be used as an escape character within a string when switching quote styles won\'t work.'

Multi-line strings are declared with ''' or """.

>>> triple_quoted =  '''Three single quotes or "double quotes" in a row allow for multi-line string literals.
  Line break characters, tabs and other whitespace are fully supported.

  You\'ll most often encounter these as "doc strings" or "doc tests" written just below the first line of a function or class definition.
    They\'re often used with auto documentation ✍ tools.
    '''

Strings can be concatenated using the + operator. This method should be used sparingly, as it is not very performant or easily maintained.

language = "Ukrainian"
number = "nine"
word = "дев'ять"

sentence = word + " " + "means" + " " + number + " in " + language + "."

>>> print(sentence)
...
"дев'ять means nine in Ukrainian."

If a list, tuple, set or other collection of individual strings needs to be combined into a single str, <str>.join(<iterable>), is a better option:

# str.join() makes a new string from the iterables elements.
>>> chickens = ["hen", "egg", "rooster"]
>>> ' '.join(chickens)
'hen egg rooster'

# Any string can be used as the joining element.
>>> ' :: '.join(chickens)
'hen :: egg :: rooster'

>>> ' 🌿 '.join(chickens)
'hen 🌿 egg 🌿 rooster'

Code points within a str can be referenced by 0-based index number from the left:

creative = '창의적인'

>>> creative[0]
'창'

>>> creative[2]
'적'

>>> creative[3]
'인'

Indexing also works from the right, starting with a -1-based index:

creative = '창의적인'

>>> creative[-4]
'창'

>>> creative[-2]
'적'

>>> creative[-1]
'인'

There is no separate “character” or "rune" type in Python, so indexing a string produces a new str of length 1:

>>> website = "exercism"
>>> type(website[0])
<class 'str'>

>>> len(website[0])
1

>>> website[0] == website[0:1] == 'e'
True

Substrings can be selected via slice notation, using <str>[<start>:stop:<step>] to produce a new string. Results exclude the stop index. If no start is given, the starting index will be 0. If no stop is given, the stop index will be the end of the string.

moon_and_stars = '🌟🌟🌙🌟🌟⭐'
sun_and_moon = '🌞🌙🌞🌙🌞🌙🌞🌙🌞'

>>> moon_and_stars[1:4]
'🌟🌙🌟'

>>> moon_and_stars[:3]
'🌟🌟🌙'

>>> moon_and_stars[3:]
'🌟🌟⭐'

>>> moon_and_stars[:-1]
'🌟🌟🌙🌟🌟'

>>> moon_and_stars[:-3]
'🌟🌟🌙'

>>> sun_and_moon[::2]
'🌞🌞🌞🌞🌞'

>>> sun_and_moon[:-2:2]
'🌞🌞🌞🌞'

>>> sun_and_moon[1:-1:2]
'🌙🌙🌙🌙'

Strings can also be broken into smaller strings via <str>.split(<separator>), which will return a list of substrings. The list can then be further indexed or split, if needed. Using <str>.split() without any arguments will split the string on whitespace.

>>> cat_ipsum = "Destroy house in 5 seconds mock the hooman."
>>> cat_ipsum.split()
...
['Destroy', 'house', 'in', '5', 'seconds', 'mock', 'the', 'hooman.']


>>> cat_ipsum.split()[-1]
'hooman.'


>>> cat_words = "feline, four-footed, ferocious, furry"
>>> cat_words.split(', ')
...
['feline', 'four-footed', 'ferocious', 'furry']

Separators for <str>.split() can be more than one character. The whole string is used for split matching.

>>> colors = """red,
orange,
green,
purple,
yellow"""

>>> colors.split(',\n')
['red', 'orange', 'green', 'purple', 'yellow']

Strings support all common sequence operations. Individual code points can be iterated through in a loop via for item in <str>. Indexes with items can be iterated through in a loop via for index, item in enumerate(<str>).

>>> exercise = 'လေ့ကျင့်'

# Note that there are more code points than perceived glyphs or characters
>>> for code_point in exercise:
...    print(code_point)
...
လ
ေ
့
က
ျ
င
်
့

# Using enumerate will give both the value and index position of each element.
>>> for index, code_point in enumerate(exercise):
...    print(index, ": ", code_point)
...
0 :  လ
1 :  ေ
2 :  ့
3 :  က
4 :  ျ
5 :  င
6 :  ်
7 :  ့