第822页 | Learning Python | 阅读 ‧ 电子书库

Sequence Operations

Besides method calls, all the usual generic sequence operations you know (and possibly love) from Python 2.X strings and lists work as expected on both str and bytes in 3.0; this includes indexing, slicing, concatenation, and so on. Notice in the following that indexing a bytes object returns an integer giving the byte’s binary value; bytes really is a sequence of 8-bit integers, but it prints as a string of ASCII-coded characters when displayed as a whole for convenience. To check a given byte’s value, use the chr built-in to convert it back to its character, as in the following:

>>> B = b'spam'                  # A sequence of small ints
>>> B                            # Prints as ASCII characters
b'spam'

>>> B[0]                         # Indexing yields an int
115
>>> B[-1]
109

>>> chr(B[0])                    # Show character for int
's'
>>> list(B)                      # Show all the byte's int values
[115, 112, 97, 109]

>>> B[1:], B[:-1]
(b'pam', b'spa')

>>> len(B)
4

>>> B + b'lmn'
b'spamlmn'
>>> B * 4
b'spamspamspamspam'