Becoming a Pythonist

Becoming a PythonistBecoming a Pythonist

What is Python?
Python is a high-level, interpreted, interactive and object oriented-
scripting language
Python is a case sensitive programming language
Very clear syntax + large and comprehensive standard library
Can run on many platform: Windows, Linux, Mactonish

History of Python
Created in 1990 by Guido Von Rossum
Python is derived from many other languages, including ABC,
Modula-3, C, C++, Algol-68, SmallTalk, and Unix shell and other
scripting languages.

Why Python?
 Python is robust
 Python is flexible
 Designed to be easy to learn and use
 Clean, clear syntax
 Very few Keywords
 Highly Portable
 Python reduces time to market
 Python is free

Productivity
 Reduced development time
code is 2-10x times shorter than C, C++, Java
 Improved Program Maintenance
Code is extremely readable
 Less Training
Language is very easy to learn

What is it used for?
 Web Scripting
 Database applications
 GUI Applications
 Steering scientific Applications
 XML Processing
 Gaming, Images, Serial Ports, Robots and More..

Python Vs Java
 Code 5-10 times more concise
 Dynamic typing
 Much Quicker Development
No compilation Phase
Less typing
 Yes, it runs slower
But development is faster
 Python with Java - Jython

Advantages
Readability
It Is Simple to Get Support
Fast to Learn
Reusability
Software quality
Developer Productivity
Program Portability
Support Libraries
Enjoyment

Interactive “Shell”
 Great for learning the language
 Great for experimenting with the library
 Type statements or expressions at prompt:
 $python
>>> print “Hello, World”
Hello, World
>>>

Variable Types
 Int a=1 a=1
 a=2 a=2
 Int b = a b=a

Basic Datatypes
Integers (default for numbers)
z = 5 / 2 # Answer is 2, integer division.
Floats
x = 3.456
Strings
Can use “” or ‘’ to specify. “abc” ‘abc’ (Same thing.)
“““a‘b“c”””
Boolean
True and False

Whitespace and Comment
 There are no braces to indicate blocks of code for class and
function definitions or flow control
 Standard indentation is 4 spaces or one tab
# First comment
if True:
print "True"
else:
print "False"

Look at a sample of code…
x = 34 - 23 # A comment.
y = “Hello” # Another one.
z = 3.45
if z == 3.45 or y == “Hello”:
x = x + 1
y = y + “ World” # String concat.
print x
print y
>>> 12
>>> Hello World

String Operations
>>> “hello”.upper()
‘HELLO’
>>> print “%s xyz %d” % (“abc”, 34)
abc xyz 34
>>> names = [“Ben", “Chen", “Yaqin"]
>>> ", ".join(names)
‘Ben, Chen, Yaqin‘
>>> " ".join(names)
'BenChenYaqin'

Lists
 Lists are similar to arrays in C
 It can store same data type as well as different data type.
list = [ 'abcd', 786 , 2.23, 'john', 70.2 ]
>>> list[0]
'abcd'
>>> len(list)
5
>>> [1,2,3]+[4,5,6]
[1,2,3,4,5,6]
>>> range(1,5)
[1,2,3,4]

Built-in List Functions & Methods:
list = ['dora', 55, 'ram', 355.8]
>>> list.append(obj) : list.append('guru') → ['dora', 55, 'ram', 355.8,
'guru']
>>>list.count(obj) : list.count('ram') →1
>>>list.index(obj) : list.index(55) → 1
>>>list.remove(obj) : list.remove(355.8) → ['dora', 55, 'ram', 'guru']
>>>list.reverse() : list.reverse() → ['guru', 'ram', 55, 'dora']
>>>list.pop() : list.pop() → ['guru', 'ram', 55]
>>>list[0:2] : list[0:2] → ['guru', 'ram']

Tuples
 Tuples are sequences, just like lists.
 Tuples cannot be updated
 read-only lists
>>>tuple = ( 'abcd', 786 , 2.23, 'john', 70.2 )
>>> tuple[0]
'abcd'
>>> len(tuple)
5
>>> (1,2,3)+(4,5,6)
(1,2,3,4,5,6)
>>>min(tuple)
2.23

Dictionary
 Dictionaries consist of pairs of keys and their corresponding
values.
 Duplicate key is not allowed.
 Keys must be immutable.
 Dictionaries are indexed by keys.
>>> dict = {'Name': 'Zara', 'Age': 7, 'Class': 'First'};
>>>dict['Name']
Zara
>>>del dict['Name']
{'Age': 7, 'Class': 'First'}
>>>len(dict)
2

Built-in Dictionary Functions
dict = {'Name': 'Zara', 'Age': 7, 'Class': 'First'};
>>> dict.copy() : dict1 = dict.copy() → {'Name': 'Zara', 'Age':
7, 'Class': 'First'};
>>>dict.clear() : dict1.clear() →{}
>>>dict.get(key) : dict.get('Age') → 7
>>>dict.has_key(key) : dict.has_key('Age') → True
>>>dict.items() : dict.items() → [('Age', 7), ('Name',
'Zara'), ('Class', 'First')]
>>>dict.keys() : dict.keys() →['Age', 'Name', 'Class']
>>>dict.update(dict2) : dict.update(dict2)
>>>dict.values() : dict.values() → [7, 'Zara', 'First']

Python Loops
For Loop :
for n in range(1, 4):
print "This is the number"
While Loop:
n = 3
while n > 0:
print n, "is a nice number."
n = n – 1

Defining a Function
def sum(numbers):
"""Finds the sum of the numbers in a list."""
total = 0
for number in numbers:
total = total + number
return total
>>>sum(range(1, 5))
>>>10

Classes
 Classes usually have methods. Methods are functions which
always take an instance of the class as the first argument.
>>> Class Foo:
... def __init__(self):
... self.member = 1
... def get_member(self):
... return self.member
...
>>> f = Foo()
>>> f.get_member()
>>> 1

Python Modules
 Collection of stuff in foo.py file
 A module is a file consisting of Python code
 A module can define functions, classes, and variables.
 import math
content = dir(math)
['__doc__', '__file__', '__name__', 'acos', 'asin', 'atan', 'atan2', 'ceil', 'cos',
'cosh', 'degrees', 'e', 'exp', 'fabs', 'floor', 'fmod', 'frexp', 'hypot', 'ldexp',
'log','log10', 'modf', 'pi', 'pow', 'radians', 'sin', 'sinh', 'sqrt', 'tan', 'tanh']

Packages in Python
 Collection of modules in directory
 Must have __init__.py and contains subpackages.
 Consider a file Pots.py available in Phone directory.
Phone/Isdn.py file having function Isdn()
Phone/G3.py file having function G3()
 # Now import your Phone Package(__init__.py).
import Phone
Phone.Pots()
Phone.Isdn()
Phone.G3()

Python Exceptions Handling
 An exception is a Python object that represents an error.
 When a Python script raises an exception, it must either handle
the exception immediately otherwise it would terminate and
come out.
 try:
----
except Exception :
---
else:
---
 try:
---
finally:
---

Web Frameworks for Python
 Collection of packages or modules which allow developers to
write Web applications
 Zope2
 Web2py
 Pylons
 TurboGears
 Django

Becoming a Pythonist

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