--- a/day2/cheatsheet2.tex Mon Nov 23 10:55:43 2009 +0530
+++ b/day2/cheatsheet2.tex Tue Nov 24 11:00:52 2009 +0530
@@ -26,64 +26,207 @@
\large{FOSSEE}
\end{center}
\section{Basic Looping}
-\typ{while}
+\subsection{\typ{while}}
\begin{lstlisting}
In []: a, b = 0, 1
-In []: while b < 10:
+In []: while b < 10:
...: print b,
...: a, b = b, a + b # Fibonacci Sequence
+ ...:
\end{lstlisting}
+Basic syntax of \typ{while} loop is:
+\begin{lstlisting}
+while condition:
+ statement1
+ statement2
+\end{lstlisting}
+All the statements are executed, till the condition statement evaluates to True.
+\subsection{\typ{for} and \typ{range}}
+\typ{range(start, stop, step)}\\
+returns a list containing an arithmetic progression of integers.\\
+Of the arguments mentioned above, both start and step are optional.\\
+For example, if we skip third argument, i.e \typ{step}, then default value is 1. So:
+\begin{lstlisting}
+In []: range(1,10)
+Out[]: [1, 2, 3, 4, 5, 6, 7, 8, 9]
+\end{lstlisting}
+\textbf{Note:} stop value is not included in the list.\\
+Similarly if we don't pass \typ{start} argument, default is taken to be 0.
+\begin{lstlisting}
+In []: range(10)
+Out[]: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
+\end{lstlisting}
+In case \typ{step} is mentioned, the jump between consecutive members of the list would be equal to that.
+\begin{lstlisting}
+In []: range(1,10,2)
+Out[]: [1, 3, 5, 7, 9]
+\end{lstlisting}
+%Notice the jump between two consecutive elements is 2, i.e step.\\
\typ{for} and \typ{range}\\
-\typ{range([start,] stop[, step])}
+As mentioned previously \typ{for} in Python is used to iterate through the list members. So \typ{for} and \typ{range} can be used together to iterate through required series. For example to get square of all numbers less then 5 and greater then equal to 0, code can be written as:
\begin{lstlisting}
-In []: for i in range(3, 10, 2):
+In []: for i in range(5):
....: print i, i * i
+ ....:
+ ....:
+0 0
+1 1
+2 4
3 9
-5 25
-7 49
-9 81
+4 16
+\end{lstlisting}
+
+\section{list}
+\begin{lstlisting}
+In []: num = [1, 2, 3, 4] # Initializing a list
+In []: num
+Out[]: [1, 2, 3, 4]
+\end{lstlisting}
+\subsection{Accessing individual elements}
+\begin{lstlisting}
+In []: num[1]
+Out[]: 2
+\end{lstlisting}
+\textbf{Note:} Index of list starts from 0.
+\begin{lstlisting}
+In []: num[5] # ERROR: throws a index error
+IndexError: list index out of range
+In []: num[-1]
+Out[]: 4
\end{lstlisting}
-List methods (Contd.)
+\textbf{Note: }\typ{-1} points the last element in a list. Similarly to access third last element of a list one can use:
+\begin{lstlisting}
+In []: num[-3]
+Out[]: 2
+\end{lstlisting}
+\subsection{Adding lists and elements}
+\begin{lstlisting}
+In []: num += [9, 10, 11] # Adding two lists
+In []: num
+Out[]: [1, 2, 3, 4, 9, 10, 11]
+\end{lstlisting}
+\typ{list} provides \typ{append} function to append objects at the end.
+\begin{lstlisting}
+In []: num = [1, 2, 3, 4]
+In []: num.append(-2)
+In []: num
+Out[]: [1, 2, 3, 4, -2]
+\end{lstlisting}
+%% In []: num += [-5]
+%% In []: num
+%% Out[]: [1, 2, 3, 4, -2, -5]
+Working of \typ{append} is different from \typ{+} operator on list. Till here both will behave as same. But in following case:
\begin{lstlisting}
In []: num = [1, 2, 3, 4]
-In []: num.append([9, 10, 11])
+
+In []: num + [9, 10, 11]
+Out[]: [1, 2, 3, 4, 9, 10, 11]
+
+In []: num.append([9, 10, 11]) # appending a list to a list
+
In []: num
-Out[]: [1, 2, 3, 4, [9, 10, 11]]
+Out[]: [1, 2, 3, 4, [9, 10, 11]] # last element is a list
+\end{lstlisting}
+when one attempts to append a list(in above case [9, 10, 11]) to a list(num) it adds list as a single element. So the resulting list will have a element which itself is a list. But \typ{+} operator would simply add the elements of second list.\\
+\subsection{Miscellaneous}
+\begin{lstlisting}
In []: num = [1, 2, 3, 4]
-In []: num.extend([5, 6, 7])
+In []: num.extend([5, 6, 7]) # extend list by adding elements
In []: num
Out[]: [1, 2, 3, 4, 5, 6, 7]
-In []: num.reverse()
+In []: num.reverse() # reverse the current list
In []: num
Out[]: [7, 6, 5, 4, 3, 2, 1]
-In []: num.remove(6)
+In []: num.remove(6) # removing first occurrence of 6
In []: num
+Out[]: [7, 5, 4, 3, 2, 1]
+In []: len(num) # returns the length of list
+Out[]: 6
+In []: a = [1, 5, 3, 7, -2, 4]
+In []: min(a) # returns smallest item in a list.
+Out[]: -2
+In []: max(a) # returns largest item in a list.
+Out[]: 7
\end{lstlisting}
-Slicing: \typ{list[initial:final:step]}
+
+\subsection{Slicing}
+General syntax for getting slice out of a list is \\
+\typ{list[initial:final:step]}
\begin{lstlisting}
-In []: a[1:-1:2]
+In []: a = [1, 2, 3, 4, 5]
+In []: a[1:-1:2]
Out[]: [2, 4]
+\end{lstlisting}
+Start slice from second element(1), till the last element(-1) with step size of 2.
+\begin{lstlisting}
In []: a[::2]
Out[]: [1, 3, 5]
+\end{lstlisting}
+Start from beginning(since \typ{initial} is blank), till last of list(this time last element is included, as \typ{final} is blank), with step size of 2.\\
+Apart from using \typ{reverse} command on list, one can also use slicing in special way to get reverse of a list.
+\begin{lstlisting}
+In []: a[-1:-4:-1]
+Out[]: [5, 4, 3]
+\end{lstlisting}
+Above syntax of slice can be expressed as, ``start from last element(\typ{-1}), go till fourth last element(\typ{-4}), with step size \typ{-1}, which implies, go in reverse direction. That is, first element would be \typ{a[-1]}, second element would be \typ{a[-2]} and so on and so forth.''\\
+So to get reverse of whole list one can write following slice syntax:
+\begin{lstlisting}
In []: a[-1::-1]
Out[]: [5, 4, 3, 2, 1]
\end{lstlisting}
-Tuples(Immutable lists)
+Since \typ{final} is left blank, it will traverse through whole list in reverse manner.\\
+\textbf{Note:} While \typ{reverse} reverses the original list, slicing will just result in a instance list with reverse of original, which can be used and worked upon independently.
+%%Should we include list copy concept here?
+\subsection{Containership}
+\typ{in} keyword is used to check for containership of any element in a given list.
\begin{lstlisting}
-In []: t = (1, 2, 3, 4, 5, 6, 7, 8)
-In []: t[0] + t[3] + t[-1]
+In []: a = [2, 5, 4, 6, 9]
+In []: 4 in a
+Out[]: True
+
+In []: b = 15
+In []: b in a
+Out[]: False
+\end{lstlisting}
+\section{Tuples}
+Tuples are sequences just like Lists, but they are \textbf{immutable}, or items/elements cannot be changed in any way.
+\begin{lstlisting}
+In []: t = (1, 2, 3, 4, 5, 6, 7, 8)
+\end{lstlisting}
+\textbf{Note:} For tupels we use parantheses in place of square brackets, rest is same as lists.
+\begin{lstlisting}
+In []: t[0] + t[3] + t[-1] # elements are accessed via indices
Out[]: 13
In []: t[4] = 7 # ERROR: tuples are immutable
\end{lstlisting}
-Sets
+\textbf{Note:} elements cant be changed!
+\section{Dictionaries}
+statistics section?
+\section{Sets}
+are an unordered collection of unique elements.\\
+Creation:
+\begin{lstlisting}
+In []: s = set([2,4,7,8,5]) # creating a basic set
+In []: s
+Out[]: set([2, 4, 5, 7, 8])
+In []: g = set([2, 4, 5, 7, 4, 0, 5])
+In []: g
+Out[]: set([0, 2, 4, 5, 7]) # No repetition allowed.
+\end{lstlisting}
+Some other operations which can be performed on sets are:
\begin{lstlisting}
In []: f = set([1,2,3,5,8])
In []: p = set([2,3,5,7])
In []: f | p # Union of two sets
Out[]: set([1, 2, 3, 5, 7, 8])
-In []: g = set([2, 4, 5, 7, 4, 0, 5])
-In []: g
-Out[]: set([2, 4, 5, 7, 0]) # No repetition allowed.
+In []: f & p # Intersection of two sets
+Out[]: set([2, 3, 5])
+In []: f - p # Elements in f not is p
+Out[]: set([1, 8])
+In []: f ^ p # (f - p) | (p - f)
+Out[]: set([1, 7, 8]))
+In []: set([2,3]) < p # Test for subset
+Out[]: True
\end{lstlisting}
\end{document}