\documentclass[12pt]{article}

\title{Python: Basics}

\author{FOSSEE}

\usepackage{listings}

\lstset{language=Python,

    basicstyle=\ttfamily,

commentstyle=\itshape\bfseries, 

showstringspaces=false

}

\newcommand{\typ}[1]{\lstinline{#1}}

\usepackage[english]{babel}

\usepackage[latin1]{inputenc}

\usepackage{times}

\usepackage[T1]{fontenc}

\usepackage{ae,aecompl}

\usepackage{mathpazo,courier,euler}

\usepackage[scaled=.95]{helvet}

\begin{document}

\date{}

\vspace{-1in}

\begin{center}

\LARGE{Python: Basics}\\

\large{FOSSEE}

\end{center}

\section{Data types}

\subsection{int and float}

A whole number is a \typ{int} variable.

\begin{lstlisting}

In []: a = 13

In []: type(a)

Out[]: <type 'int'>

In []: b = -2

In []: type(b)

Out[]: <type 'int'>

In []: c = 500000000

In []: type(c)

Out[]: <type 'int'>

\end{lstlisting}

A number with decimal is a \typ{float}.

\begin{lstlisting}

In []: p = 3.141592

In []: type(p)

Out[]: <type 'float'>

\end{lstlisting}

\subsection{Complex Numbers}

\begin{lstlisting}

In []: c = 3+4j  #coeff of j specifies imaginary part

In []: abs(c) #absolute value of complex number

Out[]: 5.0

In []: c.imag #accessing imaginary part of c

Out[]: 4.0

In []: c.real #accessing real part of c

Out[]: 3.0

\end{lstlisting}

\newpage

\subsection{Boolean}

\begin{lstlisting}     

In []: a = False

In []: b = True

In []: c = True

In []: (a and b) or c #Boolean operations

Out[]: True

\end{lstlisting}

\textbf{Note:} Python is case sensitive language, \typ{True} is \typ{bool} type, but \typ{true} would be a variable. and hence following assignment fails:\\

\typ{In []: a = true}\\

\subsection{Strings}

  \begin{lstlisting}

In []: w = "hello" #w is string variable

In []: print w[1]

Out[]: e

In []: print w[-1] #last character of string

Out[]: o

  \end{lstlisting}

\textbf{Note:} For a string variable, individual elements can be accessed using indices.\\

\textbf{Note:} All slicing and striding operations works with strings as well.

  \begin{lstlisting}

In []: len(w) #function to calculate length of string

Out[]: 5

In []: w[0] = 'H' # ERROR: Strings are immutable 

  \end{lstlisting}

\subsection{String methods}

  \begin{lstlisting}

In []: a = 'Hello World' 

In []: a.startswith('Hell') # 'a' starts with 'Hell'

Out[]: True

In []: a.endswith('ld') # 'a' ends with 'ld'

Out[]: True

In []: a.upper() # all characters to upper case

Out[]: 'HELLO WORLD'

In []: a.lower() # all characters to lower case

Out[]: 'hello world'

In []: ''.join(['a', 'b', 'c'])

Out[]: 'abc'

  \end{lstlisting}

\typ{join} function joins all the list member passed as argument with the string it is called upon. In above case it is \typ{empty string}.

\begin{lstlisting}

In []: ' '.join(['a','b','c'])

Out[]: 'a b c'  

In []: ','.join(['a','b','c'])

Out[]: 'a,b,c'

\end{lstlisting}

\subsection{String formatting}

  \begin{lstlisting}

In []: x, y = 1, 1.234 #initializing two variables

In []: 'x is %s, y is %s' %(x, y)

Out[]: 'x is 1, y is 1.234'

  \end{lstlisting}

\textbf{Note:} \typ{\%s} used in above formatting specifies \typ{'str'} representation of variables. One can also try:\\

\typ{\%d} for \typ{int} representation\\

\typ{\%f} for \typ{float} representation

\begin{lstlisting}

In []: 'x is %f, y is %f' %(x, y)

Out[]: 'x is 1.000000, y is 1.234000'

In []: 'x is %d, y is %d' %(x, y)

Out[]: 'x is 1, y is 1'

\end{lstlisting}

\subsection{Arithmetic Operators}

  \begin{lstlisting}

In []: 45 % 2 # Modulo operator

Out[]: 1

In []: 5 ** 3 # Power

Out[]: 125

In []: a = 5

In []: a += 1 #increment by 1, translates to a = a + 1

In []: a *= 2

  \end{lstlisting}

\subsection{String Operations}

\begin{lstlisting}

In []: s = 'Hello'

In []: p = 'World'

In []: s + p  #concatenating two strings

Out[]: 'HelloWorld'

In []: s * 4  #repeat string for given number of times

Out[]: 'HelloHelloHelloHello'

\end{lstlisting}

\subsection{Relational and Logical Operators}

\begin{lstlisting}

In []: p, z, n = 1, 0, -1 #initializing three variables

In []: p == n  #equivalency check

Out[]: False

In []: p >= n 

Out[]: True

In []: n < z < p #finding largest number among three

Out[]: True

In []: p + n != z

Out[]: False

\end{lstlisting}

\subsection{Built-ins}

\begin{lstlisting}

In []: int(17 / 2.0) #converts arguments to integer

Out[]: 8

In []: float(17 / 2) #argument is already integer(17 / 2 = 8)

Out[]: 8.0

In []: str(17 / 2.0) #converts to string

Out[]: '8.5'

In []: round( 7.5 ) 

Out[]: 8.0

\end{lstlisting}

\subsection{Console Input}

\begin{lstlisting}

In []: a = raw_input('Enter a value: ')

Enter a value: 5

\end{lstlisting}

\textbf{Note:} \typ{raw_input} always returns string representation of user input and hence:

\begin{lstlisting}

In []: type(a)

Out[]: <type 'str'>

\end{lstlisting}

To get integer or floating point of this input, one has to perform type conversion:\\

\typ{In []: b = int(a)}

\section{Conditionals}

\typ{if}

\begin{lstlisting}

In []: x = int(raw_input("Enter an integer:"))

In []: if x < 0:

  ...:     print 'Be positive!'

  ...: elif x == 0:

  ...:     print 'Zero'

  ...: elif x == 1:

  ...:     print 'Single'

  ...: else:

  ...:     print 'More'

\end{lstlisting}

Ternary Operator

\begin{lstlisting}

In []: a = raw_input('Enter number(Q to quit):')

In []: num = int(a) if a != 'Q' else 0

\end{lstlisting}

Above statement can be read as ``num is int of a, if a is not equal to 'Q', otherwise 0 ``

\section{Links and References}

\begin{itemize}

  \item Reference manual to describe the standard libraries  that are distributed with Python is available at \url{http://docs.python.org/library/} 

  \item To read more on strings refer to: \\ \url{http://docs.python.org/library/stdtypes.html#string-methods}

\end{itemize}

\end{document}