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# Exercise 2 : Python Basics

## Output to terminals

- print
**“hello world”** - print
**1+1**

## Variables

- integer, strings, float
- convert integer to strings and vice versa
**str(5)****int(age)**

- 5/3 =
**1.6666**(float) or**1**(int) - calculate the string length
**len()**

## Declaration (Comments)

- # comments out a line of code
- “”“ paragraph ”“” comments out one or more lines of code

## Statement

- age = 10
- print age

## Keywords

The following is a list of keywords for the Python programming language.

and | del | from | not | while |

as | elif | global | or | with |

assert | else | if | pass | yield |

break | except | import | class | |

exec | in | raise | continue | finally |

is | return | def | for | lambda |

try |

import keyword print "Python keywords: ", keyword.kwlist

## Operators

Symbol | Type | What it Does |

+ | Mathematical | Addition |

- | Mathematical | Subtraction |

* | Mathematical | Multiplication |

/ | Mathematical | Division |

% | Modulos | Returns the remainder from a division |

& | Logical | And |

pipe | Logical | Or |

« | Shift | Left Shift |

» | Shift | Right Shift |

~ | Logical | Bitwise Negation |

< | Comparison | Less than |

> | Comparison | Greater than |

== | Comparison | Equal to |

!= | Comparison | Not Equal To |

>= | Comparison | Greater than or Equal To |

⇐ | Comparison | Less than or Equal To |

= | Assignment | Assigns a value |

+= | Assignment | Adds and assigns a value |

-= | Assignment | Subtracts and Assigns a value |

*= | Assignment | Multiplies and assigns a value |

/= | Assignment | Divides and assigns a value |

%= | Assignment | Modulus and assigns |

» | Assignment | Shifts and assigns |

« | Assignment | Shifts and assigns |

And | Boolean | |

Or | Boolean | |

Not | Boolean |

other operators are

TruncatingDivision [//] Mathematical Powers [**] Bitwise XOR [^] Truncate Divides and assigns a value [//=] Powers and assigns [**=]

## Functions() and importing

def increment(x): return x+1 import math math.sqrt(4)

** Always remember the flow of execution - the identation**

## Conditions and Recursions

- Boolean & logical expressions
- 26 == 26
- True
- !=, >, <; >=, ⇐, %, and, …

- Alternative executions
- if, else, elif,
- Nested layers

- return, continue

## Iterations/loops

- while n > 20:
- for i in range(0, 20):
- for char in fruit:

while i < n: print txt for x in range(0,20): print x*x fruit = "Banana" for char in fruit: print char

**Nested loops**

for x in xrange(1,11): for y in xrange(1,11): print '%d * %d = %d' % (x,y,x*y)

**Early exit**

for x in xrange(3): if x==1: break

**For..Else**

for x in xrange(3): print x else: print 'Final x = %d' % (x)

**Strings as an iterable**

string = "Hello World" for x in string: print x

**Lists as an iterable**

collection = ['hey',5,'d'] for x in collection: print x

**Lists of lists**

list_of_lists = [ [1, 2, 3], [4, 5, 6], [7, 8, 9]] for list in list_of_lists: for x in list: print x

**Creating your own iterable**

class Iterable(object): def __init__(self,values): self.values = values self.location = 0 def __iter__(self): return self def next(self): if self.location == len(self.values): raise StopIteration value = self.values[self.location] self.location += 1 return value

## Classes

- Class Area:
- def square_area(w, h):
- area = w*h
- return area

- import Area()
- ar = Area.Area()
- print ar.squre_area(20, 20)

## Other

**Lot more stuffs can be explored and you have a vast internet.**

## Tutorial

Download this Exercise 2 Code Skeleton and follow the class tutorial.

solution to the skeleton: Exercise2_Solution

## Important sources and references

[1] http://rur-ple.sourceforge.net/en/interpreter.htm

[2] http://en.wikibooks.org/wiki/Python_Programming/Variables_and_Strings

[3] http://zetcode.com/tutorials/pythontutorial/keywords/

[4] http://www.devshed.com/c/a/Python/Python-Operators/

[5] http://docs.python.org/tutorial/inputoutput.html

[6] http://www.penzilla.net/tutorials/python/functions/