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| -rw-r--r-- | day2/cheatsheet2.tex | 187 |
1 files changed, 165 insertions, 22 deletions
diff --git a/day2/cheatsheet2.tex b/day2/cheatsheet2.tex index 1504e3c..05f248d 100644 --- a/day2/cheatsheet2.tex +++ b/day2/cheatsheet2.tex @@ -26,64 +26,207 @@ showstringspaces=false \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} +\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} -List methods (Contd.) +%% 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} |