构建C语言的union

 ctype模块提供了三种不同的方式加载dll:cdll(),windll()和oledll(),在windows下，可用动态链接库msvcrt.dll为我们提供运行时c库，位于C:\WINDOWS\System32\下，在Linux下为libc.so.6

from ctypes import *
msvcrt=cdll.msvcrt
message_string="Hello world!\n"
msvcrt.printf("Testing: %s",message_string)

 模拟C语言的union，可写为：

#!/usr/bin/env python
from ctypes import *
class barley_amount(Union):
    _fields_=[
        ("barley_long",c_long),
        ("barley_int",c_int),
        ("barley_char",c_char * 8),
    ]
value=raw_input("Enter the amount of barley to put into the beer vat:")
my_barley=barley_amount(int(value))
print "Barley amount as a long: %ld" % my_barley.barley_long
print "Barley amount as an int: %d" % my_barley.barley_int
print "Barley amount as a char: %s" % my_barley.barley_char