在 Python 2.7 中将字符串更改为字节类型

Question

In python 3.2, i can change the type of an object easily. For example :

x=0
print(type (x))
x=bytes(0)
print(type (x))

it will give me this :

<class 'int'>
<class 'bytes'>

But, in python 2.7, it seems that i can't use the same way to do it. If i do the same code, it give me this :

<type 'int'>
<type 'str'>

What can i do to change the type into a bytes type?

Answer 1

You are not changing types, you are assigning a different value to a variable.

You are also hitting on one of the fundamental differences between python 2.x and 3.x; grossly simplified the 2.x type unicode has replaced the str type, which itself has been renamed to bytes . It happens to work in your code as more recent versions of Python 2 have added bytes as an alias for str to ease writing code that works under both versions.

In other words, your code is working as expected.

Answer 2

What can i do to change the type into a bytes type?

You can't, there is no such type as 'bytes' in Python 2.7.

From the Python 2.7 documentation (5.6 Sequence Types): "There are seven sequence types: strings, Unicode strings, lists, tuples, bytearrays, buffers, and xrange objects."

From the Python 3.2 documentation (5.6 Sequence Types): "There are six sequence types: strings, byte sequences (bytes objects), byte arrays (bytearray objects), lists, tuples, and range objects."

Answer 3

In Python 2.x, bytes is just an alias for str , so everything works as expected. Moreover, you are not changing the type of any objects here – you are merely rebinding the name x to a different object.

Answer 4

May be not exactly what you need, but when I needed to get the decimal value of the byte d8 (it was a byte giving an offset in a file) i did:

a = (data[-1:])          # the variable 'data' holds 60 bytes from a PE file, I needed the last byte
                         #so now a == '\xd8'  , a string
b = str(a.encode('hex')) # which makes b == 'd8' , again a string
c = '0x' + b             # c == '0xd8' , again a string
int_value = int(c,16)    # giving me my desired offset in decimal: 216

                         #I hope this can help someone stuck in my situation

Answer 5

Just example to emphasize a procedure of turning regular string into binary string and back:

sb = "a0" # just string with 2 characters representing a byte
ib = int(sb, 16) # integer value (160 decimal)
xsb = chr(ib) # a binary string (equals '\xa0')

Now backwards

back_sb = xsb.encode('hex')
back_sb == sb # returns True