PANDAS中的错误：在基于整数索引的索引上只能有整数索引器

Question

我有一个数据框“ final”，如下所示”

                                                 link  module
0   "getstart.pdf" target="_blank"><span class="tr...  MATLAB
1   "matlab_env.pdf" target="_blank"><span class="...  MATLAB
2   "import_export.pdf" target="_blank"><span clas...  MATLAB
3   "math.pdf" target="_blank"><span class="tradem...  MATLAB
4   "data_analysis.pdf" target="_blank"><span clas...  MATLAB
5   "matlab_prog.pdf" target="_blank"><span class=...  MATLAB
6   "matlab_oop.pdf" target="_blank"><span class="...  MATLAB
7   "graphg.pdf" target="_blank"><span class="trad...  MATLAB
8   "visualize.pdf" target="_blank"><span class="t...  MATLAB
9   "buildgui.pdf" target="_blank"><span class="tr...  MATLAB
10  "apiext.pdf" target="_blank"><span class="trad...  MATLAB
11  "apiref.pdf" target="_blank"><span class="trad...  MATLAB
12  "matfile_format.pdf" target="_blank"><span cla...  MATLAB
13  "matlab_refbook.pdf" target="_blank"><span cla...  MATLAB
14  "graphics_changes.pdf" target="_blank"><span c...  MATLAB
15  "rn.pdf" target="_blank"><span class="trademar...  MATLAB
16  "../otherdocs/ode_suite.pdf" target="_blank"><...  MATLAB
17  "../otherdocs/simax.pdf" target="_blank">Spars...  MATLAB

我想用以下代码提取每一行中包含的PDF文件的名称：

for index, row in final.iterrows():
    end = final.at[row, 'link'].rfind('.pdf')+4
    str = final['link'][row][1: end] 

我跑步并在Pycharm中收到一条错误消息：

另一方面，如果我将此代码应用于特定的行，它将运行平稳：

end = final.at[7, 'link'].rfind('.pdf')+4
str = final['link'][7][1: end]

请帮助我解决此错误！谢谢您的帮助！