Little Sister's Essay

The str class offers many useful methods for working with and composing strings. These include searching, cleaning, splitting, transforming, translating, and many other techniques.

Strings are immutable sequences of Unicode code points -- individual "characters" or code points (strings of length 1) can be referenced by 0-based index number from the left, or -1-based index number from the right.

Strings can be iterated through using for item in <str> or for index, item in enumerate(<str>) syntax. They can be concatenated using the + operator or via <string>.join(<iterable>) and implement all common sequence operations.

Strings are immutable, meaning the value of a str object in memory cannot change. Functions or methods that operate on a str (like the ones we are learning about here) will return a new instance of that str object instead of modifying the original str.

Following is a small selection of Python string methods. For a complete list, see the str class in the Python docs.

<str>.title() parses a string and capitalizes the first "character" of each "word" found. In Python, this is very dependent on the language codec used and how the particular language represents words and characters. There may also be locale rules in place for a language or character set.

man_in_hat_th = 'ผู้ชายใส่หมวก'
man_in_hat_ru = 'мужчина в шляпе'
man_in_hat_ko = '모자를 쓴 남자'
man_in_hat_en = 'the man in the hat.'

>>> man_in_hat_th.title()
'ผู้ชายใส่หมวก'

>>> man_in_hat_ru.title()
'Мужчина В Шляпе'

>>> man_in_hat_ko.title()
'모자를 쓴 남자'

>> man_in_hat_en.title()
'The Man In The Hat.'

<str>.endswith(<suffix>) returns True if the string ends with <suffix>, False otherwise.

>>> 'My heart breaks. 💔'.endswith('💔')
True

>>> 'cheerfulness'.endswith('ness')
True

# Punctuation is part of the string, so needs to be included in any endswith match.
>>> 'Do you want to 💃?'.endswith('💃')
False

>> 'The quick brown fox jumped over the lazy dog.'.endswith('dog')
False

<str>.strip(<chars>) returns a copy of the str with leading and trailing <chars> removed. The code points specified in <chars> are not a prefix or suffix - all combinations of the code points will be removed starting from both ends of the string. If nothing is specified for <chars>, all combinations of whitespace code points will be removed.

# This will remove "https://", because it can be formed from "/stph:". 
>>> 'https://unicode.org/emoji/'.strip('/stph:')
'unicode.org/emoji'

# Removal of all whitespace from both ends of the str.
>>> '   🐪🐪🐪🌟🐪🐪🐪   '.strip()
'🐪🐪🐪🌟🐪🐪🐪'

>>> justification = 'оправдание'
>>> justification.strip('еина')
'оправд'

# Prefix and suffix in one step.
>>> 'unaddressed'.strip('dnue')
'address'

>>> '  unaddressed  '.strip('dnue ')
'address'

<str>.replace(<substring>, <replacement substring>) returns a copy of the string with all occurrences of <substring> replaced with <replacement substring>.

The quote used below is from The Hunting of the Snark by Lewis Carroll

# The Hunting of the Snark, by Lewis Carroll
>>> quote = '''
"Just the place for a Snark!" the Bellman cried,
   As he landed his crew with care;
Supporting each man on the top of the tide
   By a finger entwined in his hair.

"Just the place for a Snark! I have said it twice:
   That alone should encourage the crew.
Just the place for a Snark! I have said it thrice:
   What I tell you three times is true."
'''

>>> quote.replace('Snark', '🐲')
...
'\n"Just the place for a 🐲!" the Bellman cried,\n   As he landed his crew with care;\nSupporting each man on the top of the tide\n   By a finger entwined in his hair.\n\n"Just the place for a 🐲! I have said it twice:\n   That alone should encourage the crew.\nJust the place for a 🐲! I have said it thrice:\n   What I tell you three times is true."\n'

>>> 'bookkeeper'.replace('kk', 'k k')
'book keeper'