为什么我会收到此错误“ImportError: dlopen(...): Symbol not found”？当我在 python 上导入我的库时答案

【问题标题】：Why do I get this error "ImportError: dlopen(...): Symbol not found"? when I import my library on python为什么我会收到此错误“ImportError: dlopen(...): Symbol not found”？当我在 python 上导入我的库时
【发布时间】：2020-10-11 00:02:31
【问题描述】：

我一直尝试在我的 python 项目中使用一些 C 代码和 CFFI，但是当我尝试构建然后导入我构建的库时 import _chebyshev_cffi ，我收到以下错误：

ImportError: dlopen(/Users/Username/Documents/code project/_chebyshev_cffi.cpython-35m-darwin.so, 2): Symbol not found: _elementary_clenshaw_step_real
Referenced from: /Users/Username/Documents/code project/_chebyshev_cffi.cpython-35m-darwin.so
Expected in: flat namespace

我不确定这里出了什么问题，我一直无法找到有关此错误的信息，如果能提供任何帮助，我将不胜感激。我正在使用 MacOS 和 python 的 anaconda 发行版，cffi 似乎安装正确。

编辑：我可能应该补充一点，我实际期望的函数前面不应该有下划线。它应该是 ” elementary_clenshaw_step_real 而不是 _elementary_clenshaw_step_real。以下是源代码：

#!/usr/bin/env python3
# -*- coding: utf-8 -*-
"""
Created on Tue Sep  3 17:00:38 2019

@author: anonymous
"""

from cffi import FFI
ffibuilder = FFI()

ffibuilder.cdef("void elementary_clenshaw_step_real(const int dim_x, const char * restrict boundary_condition, const double * restrict wfc, const double * restrict psi, double * restrict psi_old, const double c_coef, const double one_or_two, const int add_real, const double tunneling, const double * restrict disorder);")
ffibuilder.cdef("void chebyshev_clenshaw_real(const int dim_x, const int max_order, const char * restrict boundary_condition, double * wfc, double * psi, double * psi_old, const double tunneling, const double * disorder, const double *tab_coef, const double g_times_delta_t, const double e0_times_delta_t);")

ffibuilder.set_source("_chebyshev_cffi",
r"""
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#ifdef __ICC
#include <mathimf.h>
#else
#include <math.h>
#endif
#include <complex.h>

void __inline elementary_clenshaw_step_real(const int dim_x, const char * restrict boundary_condition, const double * restrict wfc, const double * restrict psi, double * restrict psi_old, const double c_coef, const double one_or_two, const int add_real, const double tunneling, const double * restrict disorder)
{
  int i; 
  if (add_real) {
    if (strcmp(boundary_condition,"periodic") == 0) {
      psi_old[0]=one_or_two*(disorder[0]*psi[0]-tunneling*(psi[1]+psi[dim_x-1]))+c_coef*wfc[0]-psi_old[0];
      psi_old[dim_x]=one_or_two*(disorder[0]*psi[dim_x]-tunneling*(psi[dim_x+1]+psi[2*dim_x-1]))+c_coef*wfc[dim_x]-psi_old[dim_x];
      psi_old[dim_x-1]=one_or_two*(disorder[dim_x-1]*psi[dim_x-1]-tunneling*(psi[0]+psi[dim_x-2]))+c_coef*wfc[dim_x-1]-psi_old[dim_x-1] ;
      psi_old[2*dim_x-1]=one_or_two*(disorder[dim_x-1]*psi[2*dim_x-1]-tunneling*(psi[dim_x]+psi[2*dim_x-2]))+c_coef*wfc[2*dim_x-1]-psi_old[2*dim_x-1];
    } else {
      psi_old[0]=one_or_two*(disorder[0]*psi[0]-tunneling*psi[1])+c_coef*wfc[0]-psi_old[0];
      psi_old[dim_x]=one_or_two*(disorder[0]*psi[dim_x]-tunneling*psi[dim_x+1])+c_coef*wfc[dim_x]-psi_old[dim_x];
      psi_old[dim_x-1]=one_or_two*(disorder[dim_x-1]*psi[dim_x-1]-tunneling*psi[dim_x-2])+c_coef*wfc[dim_x-1]-psi_old[dim_x-1] ;
      psi_old[2*dim_x-1]=one_or_two*(disorder[dim_x-1]*psi[2*dim_x-1]-tunneling*psi[2*dim_x-2])+c_coef*wfc[2*dim_x-1]-psi_old[2*dim_x-1];
    }  
#ifdef __clang__
#else
#pragma GCC ivdep
#ifdef __ICC
#pragma distribute_point
#endif
#endif
    for (i=1;i<dim_x-1;i++) {   
      psi_old[i]=one_or_two*(disorder[i]*psi[i]-tunneling*(psi[i+1]+psi[i-1]))+c_coef*wfc[i]-psi_old[i];
    }
#ifdef __clang__    
#else
#pragma GCC ivdep
#ifdef __ICC
#pragma distribute_point
#endif
#endif
    for (i=dim_x+1;i<2*dim_x-1;i++) {         
      psi_old[i]=one_or_two*(disorder[i-dim_x]*psi[i]-tunneling*(psi[i+1]+psi[i-1]))+c_coef*wfc[i]-psi_old[i];
    }    
  } else { 
    if (strcmp(boundary_condition,"periodic") == 0) {
      psi_old[0]=one_or_two*(disorder[0]*psi[0]-tunneling*(psi[1]+psi[dim_x-1]))-c_coef*wfc[dim_x]-psi_old[0];
      psi_old[dim_x]=one_or_two*(disorder[0]*psi[dim_x]-tunneling*(psi[dim_x+1]+psi[2*dim_x-1]))+c_coef*wfc[0]-psi_old[dim_x];
      psi_old[dim_x-1]=one_or_two*(disorder[dim_x-1]*psi[dim_x-1]-tunneling*(psi[0]+psi[dim_x-2]))-c_coef*wfc[2*dim_x-1]-psi_old[dim_x-1] ;
      psi_old[2*dim_x-1]=one_or_two*(disorder[dim_x-1]*psi[2*dim_x-1]-tunneling*(psi[dim_x]+psi[2*dim_x-2]))+c_coef*wfc[dim_x-1]-psi_old[2*dim_x-1];
    } else {
      psi_old[0]=one_or_two*(disorder[0]*psi[0]-tunneling*psi[1])-c_coef*wfc[dim_x]-psi_old[0];
      psi_old[dim_x]=one_or_two*(disorder[0]*psi[dim_x]-tunneling*psi[dim_x+1])+c_coef*wfc[0]-psi_old[dim_x];
      psi_old[dim_x-1]=one_or_two*(disorder[dim_x-1]*psi[dim_x-1]-tunneling*psi[dim_x-2])-c_coef*wfc[2*dim_x-1]-psi_old[dim_x-1] ;
      psi_old[2*dim_x-1]=one_or_two*(disorder[dim_x-1]*psi[2*dim_x-1]-tunneling*psi[2*dim_x-2])+c_coef*wfc[dim_x-1]-psi_old[2*dim_x-1];      
    }  
#ifdef __clang__
#else
#pragma GCC ivdep
#ifdef __ICC
#pragma distribute_point
#endif
#endif    
    for (i=1;i<dim_x-1;i++) {   
      psi_old[i]=one_or_two*(disorder[i]*psi[i]-tunneling*(psi[i+1]+psi[i-1]))-c_coef*wfc[i+dim_x]-psi_old[i];
    }
#ifdef __clang__
#else    
#pragma GCC ivdep
#ifdef __ICC
#pragma distribute_point
#endif
#endif
    for (i=dim_x+1;i<2*dim_x-1;i++) {         
      psi_old[i]=one_or_two*(disorder[i-dim_x]*psi[i]-tunneling*(psi[i+1]+psi[i-1]))+c_coef*wfc[i-dim_x]-psi_old[i];
    }        
  }    
  return;
}  

void chebyshev_clenshaw_real(const int dim_x, const int max_order,  const char * restrict boundary_condition, double * restrict wfc, double * restrict psi, double * restrict psi_old, const double tunneling, const double * restrict disorder, const double * restrict tab_coef, const double g_times_delta_t, const double e0_times_delta_t)
{
  int i, order;
  double argument;
  double cos_phase;
  double sin_phase;
  for (i=0;i<2*dim_x;i++) {
    psi[i] = tab_coef[max_order] * wfc[i];
  }
  elementary_clenshaw_step_real(dim_x, boundary_condition, wfc, psi, psi_old, tab_coef[max_order-1], 2.0, 0, tunneling, disorder);
// WARNING: max_order MUST be an even number, otherwise disaster guaranteed  
  for (order=max_order-2;order>1;order-=2) {  
//    printf("order = %d %d %lf %lf\n",order,(order+1)%2,tab_coef[order],tunneling); 
    elementary_clenshaw_step_real(dim_x, boundary_condition, wfc, psi_old, psi, tab_coef[order], 2.0, 1, tunneling, disorder);
    elementary_clenshaw_step_real(dim_x, boundary_condition, wfc, psi, psi_old, tab_coef[order-1], 2.0, 0, tunneling, disorder);
  }
  elementary_clenshaw_step_real(dim_x, boundary_condition, wfc, psi_old, psi, tab_coef[0], 1.0, 1, tunneling, disorder);
// apply nonlinear shift
  if (g_times_delta_t==0.0) {
    cos_phase=cos(e0_times_delta_t);    
    sin_phase=sin(e0_times_delta_t);
#ifdef __clang__
#else
#pragma GCC ivdep
#endif
    for (i=0;i<dim_x;i++) {
      wfc[i] = psi[i]*cos_phase+psi[i+dim_x]*sin_phase;
      wfc[i+dim_x] = psi[i+dim_x]*cos_phase-psi[i]*sin_phase;
   }  
  } else {
#ifdef __clang__
#else
#pragma GCC ivdep
#endif
    for (i=0;i<dim_x;i++) {
      argument =  e0_times_delta_t+g_times_delta_t*(psi[i]*psi[i]+psi[i+dim_x]*psi[i+dim_x]);
      wfc[i] = psi[i]*cos(argument)+psi[i+dim_x]*sin(argument);
      wfc[i+dim_x] = psi[i+dim_x]*cos(argument)-psi[i]*sin(argument);
    }
  }  
  return;
} 


""")

if __name__ == "__main__":
  ffibuilder.compile(verbose=True)

【问题讨论】：

嗨！为了让我们能够为您提供帮助，您需要提供更多详细信息，例如源代码。出现此错误的原因有很多。例如，gcc 可能没有将此.so 与您的实际库链接（您是否将库放在libraries=[] 中的set_source() 中？），但这只是许多可能性中的一种。前导下划线在您的系统上可能是正常的和预期的。
嗨，我在原始问题中添加了源代码。我没有提供任何图书馆，因为我不使用图书馆。感谢您的帮助。

标签： python importerror python-cffi

【解决方案1】：

问题在于用void __inline 声明函数。我不完全确定为什么，但它似乎同时使该函数“强制内联”（因此在编译后没有主体）和“非静态”（因此带有外部符号）。这可能是导致问题的原因。如果您删除__inline 或在void __inline 前面添加static，则一切正常。如果您询问有关 C 的问题，您可能会获得更多信息。

【讨论】：