Python Structure & Union

>>> class myclass(Union):

...     _fields_ = [("c_long", c_long),("c_char", c_char*8)]

...

>>> s = myclass(2)

>>> s

<__main__.myclass object at 0x01D2B800>

>>> s = myclass('ssss')  ### This Error I still can not figure out, why a structure can not ###constructed with a string as defined

Traceback (most recent call last):

  File "<stdin>", line 1, in <module>

TypeError: an integer is required

>>> s = myclass(22)

>>> s  ### s is just a pointer to the sturcture; if you wanna access it, you need use dot operator

<__main__.myclass object at 0x01D2B8A0>

>>> print(s)

<__main__.myclass object at 0x01D2B8A0>

>>> print(byref(s)) ### just like the location of the pointer s

<cparam 'P' (01D2B8C8)>

>>> print("helld{}".format(s))

helld<__main__.myclass object at 0x01D2B8A0>

>>> print("helld{:d}".format(s))

Traceback (most recent call last):

  File "<stdin>", line 1, in <module>

ValueError: Unknown format code 'd' for object of type 'str'

>>> print("helld{:ld}".format(s))

Traceback (most recent call last):

  File "<stdin>", line 1, in <module>

ValueError: Invalid conversion specification

>>> print("helld{:d}".format(s))

Traceback (most recent call last):

  File "<stdin>", line 1, in <module>

ValueError: Unknown format code 'd' for object of type 'str'

 

### Definition of the stucture in Python

>>> class myStructure(Structure):

...     _fields_ = [("int", c_int),("long", c_long),("char", c_char*8)]

...

>>> s = myStructure("good")

Traceback (most recent call last):

  File "<stdin>", line 1, in <module>

TypeError: an integer is required

>>> s = myStructure(22, 22, "dddd")

Traceback (most recent call last):

  File "<stdin>", line 1, in <module>

TypeError: expected string, str found

### for construction, the third argument is char, thus we need a prefix b attached

>>> s = myStructure(22, 22, b"ssss")

 

>>> print(s.int)

22

 

>>> s = myclass(2222222)

>>> s.c_char

b'\x8e\xe8!'

>>> s.c_long

2222222

>>>