Merge lp:~nickmeek/practical-programming/2014 into lp:practical-programming

[Nick Meek]

Lectures 8 and 9

[lp:~nickmeek/practical-programming/2014]

102. By Nick Meek on 2013-12-17

Added a few easy exercises

103. By Nick Meek on 2013-12-17

Pull from repo

Unmerged revisions

103. By Nick Meek on 2013-12-17

Pull from repo

102. By Nick Meek on 2013-12-17

Added a few easy exercises

101. By Nick Meek on 2013-12-17

Pull from repo

100. By Nick Meek on 2013-12-17

Editing exercises again

99. By Nick Meek on 2013-12-16

Mainly changes to exercises. I inserted a few at the beginning to emphasis the read a file, process the contents, write out a new file process.

=== modified file 'files_modules.tex'
--- files_modules.tex	2013-12-16 00:09:32 +0000
+++ files_modules.tex	2013-12-17 02:10:38 +0000
@@ -126,6 +126,7 @@
 \end{pythonInteractive}
 
 \section{Processing things from a file}
+\label{section-processing-from-file}
 
 You would normally read information from a file in a Python program
 because you want to do something with it.  Let's try counting the
@@ -371,41 +372,83 @@
   location of a file.
 \item[text file:] A file that contains printable characters organized
   into lines separated by newline characters.
-\item[list:] A sequence of values separated by commas and surrounded by square braces. E.g. \pythoninline{[1, 2, 3]} or \pythoninline{['comma', 'separated', 'values']}.
+\item[list:] A sequence of values separated by commas and surrounded 
+by square braces. E.g. \pythoninline{[1, 2, 3]} or \pythoninline{['comma', 'separated', 'values']}.
 \end{description}
 
 \section{Laboratory exercises}
 
 \begin{enumerate}
+
 \item Write a program/script that will open a file (you can specify
   the filename in your code) for reading and print its
   contents to the screen. 
-\item Extend your program from the first question so that it asks the
-  user for a file to print, and then prints out the contents of that
-  file. 
+
+\item Extend your program so that at the end of printing out the 
+contents of the file it also prints the number of words in the string. 
+For instance if the file contained 
+the string "Be as happy as possible" the output would look like:
+
+\begin{minipage}{\textwidth}
+\begin{pythonInteractive}
+Be as happy as possible
+Words = 5
+\end{pythonInteractive}
+\end{minipage}
+
+\item Extend your program so that at the end of printing out the 
+contents of the file prints the number of words in the string 
+\emph{and} the average word length. 
+For instance if the file contained 
+the string "Be as happy as possible" the output would look like:
+
+\begin{minipage}{\textwidth}
+\begin{pythonInteractive}
+Be as happy as possible
+Words = 5 Average Length = 3.8
+\end{pythonInteractive}
+\end{minipage}
+\emph{Hint}: Once you have the words in a list you can iterate (step) through 
+the list using a \pythoninline{for} loop to access each word in turn and add its 
+length to a running total. 
+
+\item Extend your program so that it creates a new string containing the
+text from the file with the word count and average word length added to the end.
+ It should then write the string to a new file. For instance, if the original input 
+ file was called \pythoninline{infile.txt} then the new file should be 
+ called \pythoninline{infile\_new.txt}.
+  
+\item Extend your program further so that it asks the
+  user for a file to print - rather than having it hard-coded in the program.   
+  
 \item Extend your program so that it first prints out all the files in
   the current working directory before asking for a file to print.
   \emph{Hint:} use the \pythoninline{os.listdir(".")} function to list
   the files in the current directory (don't forget to
   \pythoninline{import os} first). \label{ex-fm-listfiles}
+  
 \item Put the code from Section \ref{sec-files-unifying} into a script and run
   it to see that it works. Now extend the program so that it asks the
   user for a web-page to open, then opens it and prints all the links
   in that page. \label{ex-fm-web}
+  
 \item \emph{Extension Exercise:} Extend your answer from Question
   \ref{ex-fm-listfiles} so that if the requested file is a directory
   it will list the contents of the directory instead of printing the
   contents of a file. Make use of the function
   \pythoninline{os.path.isdir} to tell if a given file is a directory.
+  
 \item \emph{Extension Exercise:} Modify your program from Question
   \ref{ex-fm-web} so that it lists all links in the web page, then
   prints all the links in one of those web pages as well.
+  
 \item \emph{Extension Exercise:} Adapt \myurl{film\_critic.py} from
   Exercise \ref{sec-ff-critic} and instead of printing the program's
   output to the screen, write it to a new file called
   \myurl{new\_file.txt}.
   Make sure the output still contains line breaks in the appropriate
-  places. 
+  places.
+  
 \item \emph{Extension Exercise:} Write a program that reads in a file
   and calculates the average word length. The code at the end of
   Section \ref{sec-files-unifying} in the book is a good starting place. 

=== modified file 'iteration.tex'
--- iteration.tex	2013-11-21 22:47:36 +0000
+++ iteration.tex	2013-12-17 02:10:38 +0000
@@ -51,7 +51,8 @@
 x = x + 1
 \end{python}
 This means get the current value of \pythoninline{x}, add one, and
-then update \pythoninline{x} with the new value.
+then update \pythoninline{x} with the new value. We have seen this before
+ in Section \ref{section-looping-and-counting}.
 If you try to update a variable that doesn't exist, you get an error,
 because Python evaluates the expression on the right side of the
 assignment operator before it assigns the resulting value to the name
@@ -127,8 +128,10 @@
 computers do well and people do poorly.
 Repeated execution of a set of statements is called \myidx{iteration}.
 Because iteration is so common, Python provides several language 
-features to make it easier. The first feature we are going to look at
-is the \pythoninline{while} statement.
+features to make it easier. We have already seen this with the \pythoninline{for} loop. 
+The \pythoninline{for} loop is a specialist loop that hides some detail from us and can 
+only be used to iterate through compound data types, like strings and lists. 
+Now we will look at a more general form of the loop the \pythoninline{while} statement.
 
 Here is a function called countdown that demonstrates the use of the
 \pythoninline{while} statement:
@@ -410,6 +413,15 @@
 
 \begin{enumerate}
 
+\item Recall the \pythoninline{pow} function. Write a function \pythoninline{my\_pow} 
+which takes two integer argument and using a \pythoninline{while} loop 
+raises the first to the power of the second.
+
+\item Recall the \% (mod) operator which calculates the remainder when one number is 
+divided by another; for instance 10 \% 3 = 1. Write a function \pythoninline{my\_mod}
+which provides the same functionality but uses a \pythoninline{while} loop. For example 
+\pythoninline{my\_mod(10, 3)} would return 1.
+
 \item Recall \pythoninline{num\_digits} from page
 \pageref{sec-counting-digits}.  What will
   \pythoninline{num\_digits(0)} return? Modify it to return

=== modified file 'strings.tex'
--- strings.tex	2013-12-16 00:56:20 +0000
+++ strings.tex	2013-12-17 02:10:38 +0000
@@ -311,7 +311,7 @@
 \end{minipage}
 Test this function to confirm that it does what we wanted it to do.
 
-\section{Looping and counting}
+\section{Looping and counting}\label{section-looping-and-counting}
 The following program counts the number of times the letter
 \pythoninline{a} appears 
 in a string and is an example of a counter pattern (more counter