added self to the Python04ex07 Komparator (#214)

Author: PlumeRoberts

module04/subject/en.subject.tex

@@ -640,15 +640,15 @@ \section*{Instructions}
 Write a class called \texttt{Komparator} whose constructor takes as an argument a pandas.DataFrame which contains the dataset.
 The class must implement the following methods, which take as input two variable names:
 \begin{itemize}
-  \item \texttt{compare\_box\_plots(categorical\_var, numerical\_var)}: displays a series of box plots 
+  \item \texttt{compare\_box\_plots(self, categorical\_var, numerical\_var)}: displays a series of box plots 
   to compare how the distribution of the numerical variable changes if we only consider 
   the subpopulation which belongs to each category. 
   There should be as many box plots as categories. 
   For example, with Sex and Height, we would compare 
   the height distributions of men vs. women with two box plots.
-  \item \texttt{density(categorical\_var, numerical\_var)}: displays the density of the numerical variable.
+  \item \texttt{density(self, categorical\_var, numerical\_var)}: displays the density of the numerical variable.
   Each subpopulation should be represented by a separate curve on the graph.
-  \item \texttt{compare\_histograms(categorical\_var, numerical\_var)}: plots the numerical variable in a separate histogram for each category.
+  \item \texttt{compare\_histograms(self, categorical\_var, numerical\_var)}: plots the numerical variable in a separate histogram for each category.
   As an extra, you can use overlapping histograms with a color code.
 \end{itemize}