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diff --git a/lecture-notes/basic-python/slides/strings_loops_lists.tex b/lecture-notes/basic-python/slides/strings_loops_lists.tex new file mode 100644 index 0000000..26d7b54 --- /dev/null +++ b/lecture-notes/basic-python/slides/strings_loops_lists.tex @@ -0,0 +1,457 @@ +\section{Strings} + +\begin{frame}[fragile] + \frametitle{What are Strings?} + \begin{itemize} + \item Anything quoted is a string + \item Single quotes, double quotes or triple single/double quotes + \item Any length --- single character, null string, \ldots + \end{itemize} + \begin{lstlisting} + In[]: 'This is a string' + In[]: "This is a string too' + In[]: '''This is a string as well''' + In[]: """This is also a string""" + In[]: '' # empty string + \end{lstlisting} +\end{frame} + +\begin{frame}[fragile] + \frametitle{Why so many?} + \begin{itemize} + \item Reduce the need for escaping + \end{itemize} + \begin{lstlisting} + In[]: "Python's strings are powerful!" + In[]: 'He said, "I love Python!"' + \end{lstlisting} + \begin{itemize} + \item Triple quoted strings can be multi-line + \item Used for doc-strings + \end{itemize} +\end{frame} + +\begin{frame}[fragile] + \frametitle{Assignment \& Operations} + \begin{lstlisting} + In[]: a = 'Hello' + In[]: b = 'World' + In[]: c = a + ', ' + b + '!' + \end{lstlisting} + \begin{itemize} + \item Strings can be multiplied with numbers + \end{itemize} + \begin{lstlisting} + In[]: a = 'Hello' + In[]: a * 5 + \end{lstlisting} +\end{frame} + +\begin{frame}[fragile] + \frametitle{Accessing Elements} + \begin{lstlisting} + In[]: print a[0], a[4], a[-1], a[-4] + \end{lstlisting} + \begin{itemize} + \item Can we change the elements? + \end{itemize} + \begin{lstlisting} + In[]: a[0] = 'H' + \end{lstlisting} + \begin{itemize} + \item Strings are immutable! + \end{itemize} +\end{frame} + +\begin{frame}[fragile] + \frametitle{Problem - Day of the Week?} + \begin{itemize} + \item Strings have methods to manipulate them + \end{itemize} + \begin{block}{Problem} + Given a list, \texttt{week}, containing names of the days of the + week and a string \texttt{s}, check if the string is a day of the + week. We should be able to check for any of the forms like, + \emph{sat, saturday, Sat, Saturday, SAT, SATURDAY} + \end{block} + \begin{itemize} + \item Get the first 3 characters of the string + \item Convert it all to lower case + \item Check for existence in the list, \texttt{week} + \end{itemize} +\end{frame} + +\begin{frame}[fragile] + \frametitle{Slicing} + \begin{lstlisting} + In[]: q = "Hello World" + In[]: q[0:3] + In[]: q[:3] + In[]: q[3:] + In[]: q[:] + In[]: q[-1:1] + In[]: q[1:-1] + \end{lstlisting} + \begin{itemize} + \item One or both of the limits, is optional + \end{itemize} +\end{frame} + +\begin{frame}[fragile] + \frametitle{Striding} + \begin{lstlisting} + In[]: q[0:5:1] + In[]: q[0:5:2] + In[]: q[0:5:3] + In[]: q[0::2] + In[]: q[2::2] + In[]: q[::2] + In[]: q[5:0:-1] + In[]: q[::-1] + \end{lstlisting} +\end{frame} + +\begin{frame}[fragile] + \frametitle{String Methods} + \begin{lstlisting} + In[]: s.lower() + In[]: s.upper() + s.<TAB> + \end{lstlisting} + \begin{itemize} + \item \alert{Strings are immutable!} + \item A new string is being returned + \end{itemize} +\end{frame} + +\begin{frame}[fragile] + \frametitle{Solution - Day of the Week?} + \begin{lstlisting} + In[]: s.lower()[:3] in week + \end{lstlisting} + OR + \begin{lstlisting} + In[]: s[:3].lower() in week + \end{lstlisting} +\end{frame} + +\begin{frame}[fragile] + \frametitle{\texttt{join} a list of strings} + \begin{itemize} + \item Given a list of strings + \item We wish to join them into a single string + \item Possibly, each string separated by a common token + \end{itemize} + \begin{lstlisting} + In[]: email_list = ["info@fossee.in", + "enquiries@fossee.in", + "help@fossee.in"] + \end{lstlisting} + \begin{lstlisting} + In[]: '; '.join(email_list) + In[]: ', '.join(email_list) + \end{lstlisting} +\end{frame} + +\section{Conditionals} + +\begin{frame}[fragile] + \frametitle{\texttt{if-else} block} + \begin{lstlisting} + In[]: a = 5 + In[]: if a % 2 == 0: + ....: print "Even" + ....: else: + ....: print "Odd" + \end{lstlisting} + \begin{itemize} + \item A code block -- \texttt{:} and indentation + \item Exactly one block gets executed in the \texttt{if-else} + \end{itemize} +\end{frame} + + +\begin{frame}[fragile] + \frametitle{\texttt{if-elif-else}} + \begin{lstlisting} + In[]: if a > 0: + ....: print "positive" + ....: elif a < 0: + ....: print "negative" + ....: else: + ....: print "zero" + \end{lstlisting} + \begin{itemize} + \item Only one block gets executed, depending on \texttt{a} + \end{itemize} +\end{frame} + +\begin{frame}[fragile] + \frametitle{\texttt{else} is optional} + \begin{lstlisting} + In[]: if user == 'admin': + ....: admin_Operations() + ....: elif user == 'moderator': + ....: moderator_operations() + ....: elif user == 'client': + ....: customer_operations() + \end{lstlisting} + \begin{itemize} + \item Note that there is no \texttt{else} block + \end{itemize} +\end{frame} + +\begin{frame}[fragile] + \frametitle{Ternary operator} + \begin{itemize} + \item \texttt{score\_str} is either \texttt{'AA'} or a string of one + of the numbers in the range 0 to 100. + \item We wish to convert the string to a number using \texttt{int} + \item Convert it to 0, when it is \texttt{'AA'} + \item \texttt{if-else} construct or the ternary operator + \end{itemize} + \begin{lstlisting} + In[]: if score_str != 'AA': + ....: score = int(score_str) + ....: else: + ....: score = 0 + \end{lstlisting} + \begin{lstlisting} + In[]: ss = score_str + In[]: score = int(ss) if ss != 'AA' else 0 + \end{lstlisting} +\end{frame} + + +\begin{frame}[fragile] + \frametitle{\texttt{pass}} + \begin{itemize} + \item \texttt{pass} is a syntactic filler + \item When a certain block has no statements, a \texttt{pass} is + thrown in + \item Mostly, when you want to get back to that part, later. + \end{itemize} +\end{frame} + +\section{Loops} + +\begin{frame}[fragile] + \frametitle{\texttt{while}} + \begin{itemize} + \item Print squares of all odd numbers less than 10 using + \texttt{while} + \end{itemize} + \begin{lstlisting} + In[]: i = 1 + + In[]: while i<10: + ....: print i*i + ....: i += 2 + \end{lstlisting} + \begin{itemize} + \item The loops runs as long as the condition is \texttt{True} + \end{itemize} +\end{frame} + +\begin{frame}[fragile] + \frametitle{\texttt{for}} + \begin{itemize} + \item Print squares of all odd numbers less than 10 using + \texttt{for} + \end{itemize} + \begin{lstlisting} + In[]: for n in [1, 2, 3]: + ....: print n + \end{lstlisting} + \begin{itemize} + \item \texttt{for} iterates over each element of a sequence + \end{itemize} + \begin{lstlisting} + In[]: for n in [1, 3, 5, 7, 9]: + ....: print n*n + + In[]: for n in range(1, 10, 2): + ....: print n*n + \end{lstlisting} + \begin{itemize} + \item \alert{range([start,] stop[, step])} + \item Returns a list; Stop value is not included. + \end{itemize} +\end{frame} + + +\begin{frame}[fragile] + \frametitle{\texttt{break}} + \begin{itemize} + \item breaks out of the innermost loop. + \item Squares of odd numbers below 10 using \texttt{while} \& + \texttt{break} + \end{itemize} + \begin{lstlisting} + In[]: i = 1 + + In[]: while True: + ....: print i*i + ....: i += 2 + ....: if i>10: + ....: break + \end{lstlisting} +\end{frame} + +\begin{frame}[fragile] + \frametitle{\texttt{continue}} + \begin{itemize} + \item Skips execution of rest of the loop on current iteration + \item Jumps to the end of this iteration + \item Squares of all odd numbers below 10, not multiples of 3 + \end{itemize} + \begin{lstlisting} + In[]: for n in range(1, 10, 2): + ....: if n%3 == 0: + ....: continue + ....: print n*n + \end{lstlisting} +\end{frame} + + +\section{Lists} + +\begin{frame}[fragile] + \frametitle{Creating Lists} + \begin{lstlisting} + In[]: empty = [] + + In[]: p = ['spam', 'eggs', 100, 1.234] + In[]: q = [[4, 2, 3, 4], 'and', 1, 2, 3, 4] + \end{lstlisting} + \begin{itemize} + \item Lists can be empty, with no elements in them + \item Lists can be heterogeneous -- every element of different kind + \end{itemize} +\end{frame} + +\begin{frame}[fragile] + \frametitle{Accessing Elements} + \begin{lstlisting} + In[]: print p[0], p[1], p[3] + + In[]: print p[-1], p[-2], p[-4] + In[]: print p[10] + \end{lstlisting} + \begin{itemize} + \item Indexing starts from 0 + \item Indexes can be negative + \item Indexes should be in the valid range + \end{itemize} +\end{frame} + +\begin{frame}[fragile] + \frametitle{Accessing Elements \& length} + \begin{lstlisting} + In[]: print p[0], p[1], p[3] + + In[]: print p[-1], p[-2], p[-4] + In[]: print len(p) + In[]: print p[10] + \end{lstlisting} + \begin{itemize} + \item Indexing starts from 0 + \item Indexes can be negative + \item Indexes should be within the \texttt{range(0, len(p))} + \end{itemize} +\end{frame} + + +\begin{frame}[fragile] + \frametitle{Adding \& Removing Elements} + \begin{itemize} + \item The append method adds elements to the end of the list + \end{itemize} + \begin{lstlisting} + In[]: p.append('onemore') + In[]: p + In[]: p.append([1, 6]) + In[]: p + \end{lstlisting} + \begin{itemize} + \item Elements can be removed based on their index OR + \item based on the value of the element + \end{itemize} + \begin{lstlisting} + In[]: del p[1] + In[]: p.remove(100) + \end{lstlisting} + \begin{itemize} + \item \alert{When removing by value, first element is removed} + \end{itemize} +\end{frame} + + +\begin{frame}[fragile] + \frametitle{Concatenating lists} + \begin{lstlisting} + In[]: a = [1, 2, 3, 4] + In[]: b = [4, 5, 6, 7] + In[]: a + b + In[]: print a+b, a, b + \end{lstlisting} + \begin{itemize} + \item A new list is returned; None of the original lists change + \end{itemize} + \begin{lstlisting} + In[]: c = a + b + In[]: c + \end{lstlisting} +\end{frame} + +\begin{frame}[fragile] + \frametitle{Slicing \& Striding} + \begin{lstlisting} + In[]: primes = [2, 3, 5, 7, 11, 13, 17, 19, 23, 29] + In[]: primes[4:8] + In[]: primes[:4] + + In[]: num = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13] + In[]: num[1:10:2] + In[]: num[:10] + In[]: num[10:] + In[]: num[::2] + In[]: num[::-1] + \end{lstlisting} +\end{frame} + +\begin{frame}[fragile] + \frametitle{Sorting} + \begin{lstlisting} + In[]: a = [5, 1, 6, 7, 7, 10] + In[]: a.sort() + In[]: a + \end{lstlisting} + \begin{itemize} + \item \texttt{sort} method sorts the list in-place + \item Use \texttt{sorted} if you require a new list + \end{itemize} + \begin{lstlisting} + In[]: a = [5, 1, 6, 7, 7, 10] + In[]: sorted(a) + In[]: a + \end{lstlisting} +\end{frame} + +\begin{frame}[fragile] + \frametitle{Reversing} + \begin{lstlisting} + In[]: a = [5, 1, 6, 7, 7, 10] + In[]: a.reverse() + In[]: a + \end{lstlisting} + \begin{itemize} + \item \texttt{reverse} method reverses the list in-place + \item Use \texttt{[::-1]} if you require a new list + \end{itemize} + \begin{lstlisting} + In[]: a = [5, 1, 6, 7, 7, 10] + In[]: a[::-1] + In[]: a + \end{lstlisting} +\end{frame} |