Detailed introduction to Python's built-in bytearray function

英文文档：

class bytearray([source[, encoding[, errors]]])

Return a new array of bytes. The bytearray class is a mutable sequence of integers in the range 0 <= x < 256. It has most of the usual methods of mutable sequences, described in Mutable Sequence Types, as well as most methods that the bytes type has, see Bytes and Bytearray Operations.

The optional source parameter can be used to initialize the array in a few different ways:

• If it is a string, you must also give the encoding (and optionally, errors) parameters; bytearray() then converts the string to bytes using str.encode().

• If it is an integer, the array will have that size and will be initialized with null bytes.

• If it is an object conforming to the buffer interface, a read-only buffer of the object will be used to initialize the bytes array.

• If it is an iterable, it must be an iterable of integers in the range <span class="pre" style="margin: 0px; padding: 0px;">0 <span class="pre" style="margin: 0px; padding: 0px;"><= <span class="pre" style="margin: 0px; padding: 0px;">x <span class="pre" style="margin: 0px; padding: 0px;">< <span class="pre" style="margin: 0px; padding: 0px;">256</span></span></span></span></span>, which are used as the initial contents of the array.

Without an argument, an array of size 0 is created.

说明：

1. The return value is a new byte array

2. When none of the three parameters are passed, a byte array with a length of 0 is returned

>>> b = bytearray()
>>> b
bytearray(b'')
>>> len(b)
0

3. When the source parameter is a string, the encoding parameter must also be provided. The function converts the string into a byte array using the str.encode method

>>> bytearray('中文')
Traceback (most recent call last):
  File "<pyshell#48>", line 1, in <module>
    bytearray(&#39;中文&#39;)
TypeError: string argument without an encoding
>>> bytearray(&#39;中文&#39;,&#39;utf-8&#39;)
bytearray(b&#39;\xe4\xb8\xad\xe6\x96\x87&#39;)

## 4 . When the source parameter is an integer, an empty byte array of the length specified by the integer is returned

>>> bytearray(2)
bytearray(b'\x00\x00')
>>> bytearray(-2) #整数需大于0，使用来做数组长度的
Traceback (most recent call last):
  File "<pyshell#51>", line 1, in <module>
    bytearray(-2)
ValueError: negative count

5. When the source parameter is a buffer that is implemented When the object object of the interface is used, the bytes will be read into the byte array in read-only mode and returned

6. When the source parameter is an iterable object, then the elements of this iterable object must conform to 0 <= x < 256 so that it can be initialized into the array

>>> bytearray([1,2,3])
bytearray(b'\x01\x02\x03')
>>> bytearray([256,2,3]) #不在0-255范围内报错
Traceback (most recent call last):
  File "<pyshell#53>", line 1, in <module>
    bytearray([256,2,3])
ValueError: byte must be in range(0, 256)

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