python字符串str和字节数组相互转化方法

实例如下：

# bytes object
b = b"example"

# str object
s = "example"

# str to bytes
bytes(s, encoding = "utf8")

# bytes to str
str(b, encoding = "utf-8")

# an alternative method
# str to bytes
str.encode(s)

# bytes to str
bytes.decode(b)