[python] string文字列の使い方

April 30, 2017

連続して並んでいる文字を連結する

>>> 'Py' 'thon'
'Python'

負のindexを指定

>>> word = 'Python'
>>> word[-1]  # last character
'n'
>>> word[-2]  # second-last character
'o'
>>> word[-6]
'P'

スライス

>>> word[:2]   # character from the beginning to position 2 (excluded)
'Py'
>>> word[4:]   # characters from position 4 (included) to the end
'on'
>>> word[-2:]  # characters from the second-last (included) to the end
'on'

大きすぎるindexを指定するとエラー

>>> word[42]  # the word only has 6 characters
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
IndexError: string index out of range

大きすぎるスライスを指定した際はエラーにならない

>>> word[4:42]
'on'
>>> word[42:]
''

文字列は不変(immutable)

>>> word[0] = 'J'
  ...
TypeError: 'str' object does not support item assignment
>>> word[2:] = 'py'
  ...
TypeError: 'str' object does not support item assignment

python