I am stuck with the following one where I want to input a file with a name in the line of `\jobnameQ.tex`. 

Here is my MWE excerpted from a bigger picture.

```
\documentclass{article}

\usepackage{lipsum}

\usepackage{filecontents}

\def\csinput{\expandafter\input{\csname\jobname Q.tex\endcsname}}

\begin{document}

\begin{filecontents}{\jobname Q.tex}
  \lipsum[1]
\end{filecontents}

\csinput

\end{document}

```

This does not input any file and does not produce any output.

However, I know that if I define `\csinput` in the manner

```
\def\csinput#1{\input{\jobname#1.tex}}

```

and call it like this, 
`\csinput{Q}` it will work. 

I would like to know why the first methodology does not work. (And how it can be remedied.)