为什么加载 libc 共享库会出现“'LibraryLoader' object is not callable”错误？

Question

来自https://en.wikipedia.org/wiki/Foreign_function_interface

ctypes 模块可以从共享库/DLL 加载 C 函数 即时并在之间自动转换简单的数据类型 Python和C语义如下：

import ctypes
libc = ctypes.CDLL( '/lib/libc.so.6' )   # under Linux/Unix
t = libc.time(None)                      # equivalent C code: t = time(NULL)
print t

在 Lubuntu 18.04 上

$ whereis libc
libc: /usr/lib/x86_64-linux-gnu/libc.a /usr/lib/x86_64-linux-gnu/libc.so /usr/share/man/man7/libc.7.gz

$ locate libc.so
/lib/i386-linux-gnu/libc.so.6
/lib/x86_64-linux-gnu/libc.so.6
/usr/lib/x86_64-linux-gnu/libc.so

$ ls -l /usr/lib/x86_64-linux-gnu/libc.so
-rw-r--r-- 1 root root 298 Apr 16 16:14 /usr/lib/x86_64-linux-gnu/libc.so

我想知道为什么加载 libc 共享库会出现“'LibraryLoader' object is not callable”错误？

$ python3 --version
Python 3.6.5

$ python3

>>> import ctypes
>>> libc=ctypes.cdll("/usr/lib/x86_64-linux-gnu/libc.so")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'LibraryLoader' object is not callable


>>> libc=ctypes.cdll("/lib/x86_64-linux-gnu/libc.so.6")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'LibraryLoader' object is not callable


>>> libc=ctypes.cdll("/lib/i386-linux-gnu/libc.so.6")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'LibraryLoader' object is not callable

另见https://unix.stackexchange.com/questions/449107/what-differences-and-relations-are-between-the-various-libc-so

Answer 1

您将小写 cdll（即 LibraryLoader）与大写 CDLL（共享库的构造函数）混淆了。

此代码将按预期工作：

libc = ctypes.CDLL("/lib/x86_64-linux-gnu/libc.so.6")