143 \section{Tests: Getting started}

   144 \begin{frame}[fragile] 

   145   \frametitle{gcd revisited!}

   146   \begin{itemize}

   147   \item Open gcd.py

   148   \end{itemize}  

   149 \begin{lstlisting}

   150     def gcd(a, b):

   151         if a % b == 0: 

   152             return b

   153         return gcd(b, a%b)

   154 

   155     print gcd(15, 65)

   156     print gcd(16, 76)

   157 \end{lstlisting}

   158   \begin{itemize}

   159   \item python gcd.py

   160   \end{itemize}

   161 \end{frame}

   162 

   163 \begin{frame}[fragile] 

   164   \frametitle{Find lcm using our gcd module}

   165   \begin{itemize}

   166   \item Open lcm.py  

   167   \item $lcm = \frac{a*b}{gcd(a,b)}$

   168   \end{itemize}  

   169 \begin{lstlisting}

   170     from gcd import gcd    

   171     def lcm(a, b):

   172         return (a * b) / gcd(a, b)

   173     

   174     print lcm(14, 56)

   175 \end{lstlisting}

   176   \begin{itemize}

   177   \item python lcm.py

   178   \end{itemize}

   179   \begin{lstlisting}

   180 5

   181 4

   182 56

   183   \end{lstlisting}    

   184 \end{frame}

   185 

   186 \begin{frame}[fragile] 

   187   \frametitle{Writing stand-alone module}  

   188 Edit gcd.py file to:

   189 \begin{lstlisting}

   190     def gcd(a, b):

   191         if a % b == 0: 

   192             return b

   193         return gcd(b, a%b)

   194 

   195     if __name__ == "__main__":        

   196         print gcd(15, 65)

   197         print gcd(16, 76)

   198 \end{lstlisting}

   199   \begin{itemize}

   200   \item python gcd.py

   201   \item python lcm.py

   202   \end{itemize}

   203 \end{frame}

   204 

   205 \begin{frame}[fragile]

   206   \frametitle{More use of main}

   207   For automating tests.

   208   \begin{lstlisting}

   209 if __name__ == '__main__':

   210     for line in open('numbers.txt'):

   211         numbers = line.split()

   212         x = int(numbers[0])

   213         y = int(numbers[1])

   214         result = (int(numbers[2]))

   215         assert gcd(x, y) == result

   216   \end{lstlisting}  

   217 \end{frame}

   218 

   219 \section{Coding Style}

   220 \begin{frame}{Readability and Consistency}

   221     \begin{itemize}

   222         \item Readability Counts!\\Code is read more often than its written.

   223         \item Consistency!

   224         \item Know when to be inconsistent.

   225       \end{itemize}

   226 \end{frame}

   227 

   228 \begin{frame}[fragile] \frametitle{A question of good style}

   229   \begin{lstlisting}

   230     amount = 12.68

   231     denom = 0.05

   232     nCoins = round(amount/denom)

   233     rAmount = nCoins * denom

   234   \end{lstlisting}

   235   \pause

   236   \begin{block}{Style Rule \#1}

   237     Naming is 80\% of programming

   238   \end{block}

   239 \end{frame}

   240 

   241 \begin{frame}[fragile]

   242   \frametitle{Code Layout}

   243   \begin{itemize}

   244         \item Indentation

   245         \item Tabs or Spaces??

   246         \item Maximum Line Length

   247         \item Blank Lines

   248         \item Encodings

   249    \end{itemize}

   250 \end{frame}

   251 

   252 \begin{frame}{Whitespaces in Expressions}

   253   \begin{itemize}

   254         \item When to use extraneous whitespaces??

   255         \item When to avoid extra whitespaces??

   256         \item Use one statement per line

   257    \end{itemize}

   258 \end{frame}

   259 

   260 \begin{frame}{Comments}

   261   \begin{itemize}

   262         \item No comments better than contradicting comments

   263         \item Block comments

   264         \item Inline comments

   265    \end{itemize}

   266 \end{frame}

   267 

   268 \begin{frame}{Docstrings}

   269   \begin{itemize}

   270         \item When to write docstrings?

   271         \item Ending the docstrings

   272         \item One liner docstrings

   273    \end{itemize}

   274 More information at PEP8: http://www.python.org/dev/peps/pep-0008/

   275 \inctime{5}

   276 \end{frame}

   277 

   278 \section{Debugging}

   279 \subsection{Errors and Exceptions}

   280 \begin{frame}[fragile]

   281  \frametitle{Errors}

   282  \begin{lstlisting}

   283 In []: while True print 'Hello world'

   284  \end{lstlisting}

   285 \pause

   286   \begin{lstlisting}

   287   File "<stdin>", line 1, in ?

   288     while True print 'Hello world'

   289                    ^

   290 SyntaxError: invalid syntax

   291 \end{lstlisting}

   292 \end{frame}

   293 

   294 \begin{frame}[fragile]

   295  \frametitle{Exceptions}

   296  \begin{lstlisting}

   297 In []: print spam

   298 \end{lstlisting}

   299 \pause

   300 \begin{lstlisting}

   301 Traceback (most recent call last):

   302   File "<stdin>", line 1, in <module>

   303 NameError: name 'spam' is not defined

   304 \end{lstlisting}

   305 \end{frame}

   306 

   307 \begin{frame}[fragile]

   308  \frametitle{Exceptions}

   309  \begin{lstlisting}

   310 In []: 1 / 0

   311 \end{lstlisting}

   312 \pause

   313 \begin{lstlisting}

   314 Traceback (most recent call last):

   315   File "<stdin>", line 1, in <module>

   316 ZeroDivisionError: integer division 

   317 or modulo by zero

   318 \end{lstlisting}

   319 \end{frame}

   320 

   321 \begin{frame}[fragile]

   322   \frametitle{Handling Exceptions}

   323   Python uses \typ{try} and \typ{except} clause.

   324   %%Revisiting the raw\_input

   325   \begin{lstlisting}

   326 a = raw_input('Enter number(Q to quit):')

   327 try:

   328     num = int(a)

   329     print num

   330 except:

   331     if a == 'Q':

   332         print 'Exiting...'

   333     else:

   334         print 'Wrong input!'      

   335   \end{lstlisting}

   336   

   337   

   338 \end{frame}

   339 

   340 %% \begin{frame}[fragile]

   341 %%   \frametitle{Solving it with \typ{try} and \typ{except}}

   342 %% \vspace{-0.2in}

   343 %%   \begin{lstlisting}

   344 %% highest = 0

   345 %% for record in open('sslc1.txt'):

   346 %%     fields = record.split(';')

   347 %%     try:

   348 %%         total = 0

   349 %%         for score_str in fields[3:8]:

   350 %%             score = int(score_str)

   351 %%             total += score

   352 %%         if total > highest:

   353 %%             highest = total

   354 %%     except:        

   355 %%         pass

   356 %% print highest

   357 %%   \end{lstlisting}

   358 %% \end{frame}

   359 \subsection{Strategy}

   360 \begin{frame}[fragile]

   361     \frametitle{Debugging effectively}

   362     \begin{itemize}

   363         \item \typ{print} based strategy

   364         \item Process:

   365     \end{itemize}

   366 \begin{center}

   367 \pgfimage[interpolate=true,width=5cm,height=5cm]{DebugginDiagram.png}

   368 \end{center}

   369 \end{frame}

   370 

   371 \begin{frame}[fragile]

   372     \frametitle{Debugging effectively}

   373     \begin{itemize}

   374       \item Using \typ{\%debug} in IPython

   375     \end{itemize}

   376 \end{frame}

   377 

   378 \begin{frame}[fragile]

   379 \frametitle{Debugging in IPython}

   380 \small

   381 \begin{lstlisting}

   382 In []: import mymodule

   383 In []: mymodule.test()

   384 ---------------------------------------------

   385 NameError   Traceback (most recent call last)

   386 <ipython console> in <module>()

   387 mymodule.py in test()

   388       1 def test():

   389 ----> 2     print spam

   390 NameError: global name 'spam' is not defined

   391 

   392 In []: %debug

   393 > mymodule.py(2)test()

   394       0     print spam

   395 ipdb> 

   396 \end{lstlisting}

   397 \inctime{15} 

   398 \end{frame}

   399 

   400 \subsection{Exercise}

   401 \begin{frame}[fragile]

   402 \frametitle{Debugging: Exercise}

   403 \small

   404 \begin{lstlisting}

   405 science = {}

   406 

   407 for record in open('sslc1.txt'):

   408     fields = record.split(';')

   409     region_code = fields[0].strip()

   410 

   411     score_str = fields[6].strip()

   412     score = int(score_str) if score_str != 'AA' 

   413                            else 0

   414 

   415     if score > 90:

   416         science[region_code] += 1

   417 

   418 pie(science.values(), labels=science.keys())

   419 savefig('science.png')

   420 \end{lstlisting}

   421 \inctime{10}

   422 \end{frame}

   423 

   424 %% \begin{frame}

   425 %%     \frametitle{Testing}

   426    

   427 %%     \begin{itemize}

   428 %%         \item Writing tests is really simple!

   429 

   430 %%         \item Using nose.

   431 

   432 %%         \item Example!

   433 %%     \end{itemize}

   434 %% \end{frame}

   435 

   436 \section{Test Driven Approach}