Extracting parts of a .sty file

Question

Can you load only some specific parts from a package while not loading the rest at all? For example, from the code below I wanted to load only the \newcommands

%theorems
\usepackage{theorem}
\newtheorem{teo}{Teorema}[section]
\newtheorem{cor}[teo]{Corol\'ario}
\newtheorem{lem}[teo]{Lema}
\newtheorem{prop}[teo]{Proposi\c{c}\~ao}
%********************************************************************
%newcommands
\providecommand{\sin}{} \renewcommand{\sin}{\hspace{2pt}\textrm{sen}}
\providecommand{\tan}{} \renewcommand{\tan}{\hspace{2pt}\textrm{tg}}
\newcommand{\N}{\mathbb{N}}
\newcommand{\Z}{\mathbb{Z}}
\newcommand{\Q}{\mathbb{Q}}
\newcommand{\R}{\mathbb{R}}
\newcommand{\C}{\mathbb{C}}

In my .tex file I would like to use for instance

\documentclass{article}
\usepackage['newcommands only']{file.sty}

or something similar to this.

Answer 1

You must add package options to decide via options which part should be loaded. A list of of nearly every keyval package can you find here: A big list of every keyval package

An example with kvoptions is:

\ProvidesPackage{file}

...

\RequirePackage{kvoptions}

\DeclareBoolOption{newcommand}
\DeclareBoolOption{theorem}

\ProcessKeyvalOptions*
....
\iffile@newcommand
   \providecommand{\sin}{} \renewcommand{\sin}{\hspace{2pt}\textrm{sen}}
   \providecommand{\tan}{} \renewcommand{\tan}{\hspace{2pt}\textrm{tg}}
   \newcommand{\N}{\mathbb{N}}
   \newcommand{\Z}{\mathbb{Z}}
   \newcommand{\Q}{\mathbb{Q}}
   \newcommand{\R}{\mathbb{R}}
   \newcommand{\C}{\mathbb{C}}
\fi
\iffile@theorem
   %use theorem
   \usepackage{theorem}
   \newtheorem{teo}{Teorema}[section]
   \newtheorem{cor}[teo]{Corol\'ario}
   \newtheorem{lem}[teo]{Lema}
   \newtheorem{prop}[teo]{Proposi\c{c}\~ao}
\fi
...
\endinput

EDIT:

In relation to the comments I present a whole minimal example. To test the different input methods use the commented usepackage.

\RequirePackage{filecontents}
\begin{filecontents}{mypackage.sty}
\ProvidesPackage{mypackage}
\RequirePackage{kvoptions}
 \SetupKeyvalOptions{%
   family=MyPack,
   prefix=MyPack@,%prefix of all command created by kvoptions
   }

\DeclareBoolOption{newcommand}
\DeclareBoolOption{theorem}

\ProcessKeyvalOptions*
\ifMyPack@newcommand
\RequirePackage{amsfonts}
   \providecommand{\sin}{} \renewcommand{\sin}{\hspace{2pt}\textrm{sen}}
   \providecommand{\tan}{} \renewcommand{\tan}{\hspace{2pt}\textrm{tg}}
   \newcommand{\N}{\mathbb{N}}
   \newcommand{\Z}{\mathbb{Z}}
   \newcommand{\Q}{\mathbb{Q}}
   \newcommand{\R}{\mathbb{R}}
   \newcommand{\C}{\mathbb{C}}
\fi
\ifMyPack@theorem
   %use theorem
   \usepackage{theorem}
   \newtheorem{teo}{Teorema}[section]
   \newtheorem{cor}[teo]{Corol\'ario}
   \newtheorem{lem}[teo]{Lema}
   \newtheorem{prop}[teo]{Proposi\c{c}\~ao}
\fi
\endinput
\end{filecontents}
\documentclass{article}
\usepackage{mypackage}
%\usepackage[newcommand]{mypackage}
%\usepackage[newcommand=true]{mypackage}
\usepackage{blindtext}
\begin{document}
\ifdefined\Q
 defined
\else
 not defined
\fi
\end{document}