Python 中的 str 是不可變序列，由Unicode 編碼點組成。
這些可能包含字母、變音符號、定位字元、數字、貨幣符號、emoji、標點符號、空格與換行字元，以及更多其他字元。
由於不可變，str 物件在記憶體中的值不會改變；看似會修改字串的方法，其實會回傳該 str 物件的新副本或新實例。
str 字面值可以用單引號'或雙引號"來宣告。需要時可以使用跳脫字元\。
>>> 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.'
多行字串則用 ''' 或 """ 來宣告。
>>> 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.
'''
字串可以用 + 運算子來串接。
這種做法應謹慎使用，因為它的效能不佳，也不容易維護。
language = "Ukrainian"
number = "nine"
word = "дев'ять"
sentence = word + " " + "means" + " " + number + " in " + language + "."
>>> print(sentence)
...
"дев'ять means nine in Ukrainian."
如果需要把 list、tuple、set 或其他由個別字串組成的集合合併成單一的 str，<str>.join(<iterable>) 會是更好的選擇：
# str.join() makes a new string from the iterables elements.
>>> chickens = ["hen", "egg", "rooster"] # Lists are iterable.
>>> ' '.join(chickens)
'hen egg rooster'
# Any string can be used as the joining element.
>>> ' :: '.join(chickens)
'hen :: egg :: rooster'
>>> ' 🌿 '.join(chickens)
'hen 🌿 egg 🌿 rooster'
# Any iterable can be used as input.
>>> flowers = ("rose", "daisy", "carnation") # Tuples are iterable.
>>> '*-*'.join(flowers)
'rose*-*daisy*-*carnation'
>>> flowers = {"rose", "daisy", "carnation"} # Sets are iterable, but output order is not guaranteed.
>>> '*-*'.join(flowers)
'rose*-*carnation*-*daisy'
>>> phrase = "This is my string" # Strings are iterable, but be careful!
>>> '..'.join(phrase)
'T..h..i..s.. ..i..s.. ..m..y.. ..s..t..r..i..n..g'
# Separators are inserted **between** elements, but can be any string (including spaces).
# This can be exploited for interesting effects.
>>> under_words = ['under', 'current', 'sea', 'pin', 'dog', 'lay']
>>> separator = ' ⤴️ under'
>>> separator.join(under_words)
'under ⤴️ undercurrent ⤴️ undersea ⤴️ underpin ⤴️ underdog ⤴️ underlay'
# The separator can be composed different ways, as long as the result is a string.
>>> upper_words = ['upper', 'crust', 'case', 'classmen', 'most', 'cut']
>>> separator = ' 🌟 ' + upper_words[0]
>>> separator.join(upper_words)
'upper 🌟 uppercrust 🌟 uppercase 🌟 upperclassmen 🌟 uppermost 🌟 uppercut'
str 中的編碼點可以用從左側算起的0-based index編號來存取：
creative = '창의적인'
>>> creative[0]
'창'
>>> creative[2]
'적'
>>> creative[3]
'인'
索引也可以從右側進行，從-1-based index開始：
creative = '창의적인'
>>> creative[-4]
'창'
>>> creative[-2]
'적'
>>> creative[-1]
'인'
Python 沒有獨立的「字元」或「rune」型別，因此對字串取索引會產生長度為 1 的新 str：
>>> website = "exercism"
>>> type(website[0])
<class 'str'>
>>> len(website[0])
1
>>> website[0] == website[0:1] == 'e'
True
子字串可以透過_切片表示法_選取，使用 <str>[<start>:stop:<step>] 產生新的字串。
結果不包含 stop 索引。
如果沒有指定 start，起始索引會是 0。
如果沒有指定 stop，stop 索引就會是字串的結尾。
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]
'🌙🌙🌙🌙'
字串也可以透過 <str>.split(<separator>) 拆解成更小的字串，這會回傳由子字串組成的 list。
之後可以視需要對它進一步取索引或再拆分。
使用不帶任何引數的 <str>.split() 會以空白字元來拆分字串。
>>> 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']
<str>.split() 的分隔符可以超過一個字元。
比對拆分位置時會使用整個字串。
>>> colors = """red,
orange,
green,
purple,
yellow"""
>>> colors.split(',\n')
['red', 'orange', 'green', 'purple', 'yellow']
字串支援所有常見序列操作。
個別的編碼點可以在迴圈中用 for item in <str> 逐一疊代。
索引_連同_項目則可以在迴圈中用 for index, item in enumerate(<str>) 逐一疊代。
>>> 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 : ့
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