Change \parskip only inside enumerate & itemize environment

Question

Is there any way that I can change \\parskip to a different value inside certain environments, namely enumerate and itemize.

I wan

Answer 1

The following addition to the preamble updates enumerate to make the suggested change:

\let\oldenumerate\enumerate% Keep a copy of \enumerate (or \begin{enumerate})
\let\endoldenumerate\endenumerate% Keep a copy of \endenumerate (or \end{enumerate})
\renewenvironment{enumerate}
  {\begin{oldenumerate}
     \setlength{\parskip}{0pt}}% Adjust \parskip to suit your needs
  {\end{oldenumerate}}

Here is a complete minimal example showing the adjustment when setting \parskip to 0pt:

\documentclass{article}
\begin{document}

\begin{enumerate}
  \item First line

    Second line
\end{enumerate}

\let\oldenumerate\enumerate
\let\endoldenumerate\endenumerate
\renewenvironment{enumerate}
  {\begin{oldenumerate}
     \setlength{\parskip}{0pt}}
  {\end{oldenumerate}}

\begin{enumerate}
  \item First line

    Second line
\end{enumerate}

\end{document}

One would do exactly the same for itemize.