Why Learn Python?

Prentice Wongvibulsin <me@prenticew.com>

http://talks.prenticew.com/pytalk09

Motivation

Why bother learning a new language?

• I already know Java!

The right language for the right job.

• Pick the right language to get the job done right.

Overview

Objective

• Intended audience: familiar with some other programming language.
• Goal: To motivate you to learn and use Python.
• Method: I will attempt to cover all the interesting and uninteresitng pieces of Python so that you may see what the language has to offer.

Lets get started...

• Interactive Top-Level
• You can follow along using Python's interactive top-level.
• IDLE for Windows and Python shell for *nix
• Source files
• Standard extension is .py
• Standard scripts are #!/usr/bin/python

Numbers

• integers:

  1, 2, 3 ... etc

• floats:

  1.0, 2.1, 3.2 ... etc

• complex:

  (1+0j), (2+3j) ... etc

• Built-in math functions:

  abs... etc

Comments

• Comments begin with the # symbol

Variables

• type checking at run-time (not compile time)
• duck typing (dynamically typed)
• strongly typed

Structure

if (x)
{
   if (y)
   {
      f1();
   }
   f2();
}

if x:
   if y:
      f1()
   f2()

Import

• Import python modules, functions or objects

Strings

• single or double quotes
• built-in string functions
• multiline strings

Lists

• Lists are surrounded by brackets and accessed with brackets

Example:

>>> l = [1,2,3,4,5,6,7,8]
>>> l[2:3]
[3]
>>> l[:3]
[1, 2, 3]
>>> l[4:]
[5, 6, 7, 8]
>>> l[:-1]
[1, 2, 3, 4, 5, 6, 7]

Map

• map(function, sequence)

Example:

>>> l = [1,-2,3,-5,10,-99]
>>> map(abs,l)
[1, 2, 3, 5, 10, 99]

Tuples

• Tuples are surrounded by parentesis and accessed the same way as lists or by expansion.

  x = (1,2,3)
  a=x[0]
  a,b,c = x
  

• Tuples are immutable.
• Tuples can be returned by functions.

  def myFc():
     ...
     return a,b,c
  a,b,c = myFc()
  

len

• len(myTupple)
• len(myList)
• len(myStr)

Dictionaries

• associative array (hash table-like)

Example:

>>> dict = {"key1":100,"key2":200}
>>> dict["key1"]
100

Formatting Strings

• Single or double quotes (no difference).

Example:

str1 = "hello"
str2 = "world"
str3 = "%s, %s." % (str1,str2)

print

Example:

>>> print "hello world"
hello world
>>> i=1
>>> print "the answer is %d" % i
the answer is 1

if

Example:

if b1:
	a=1
elif b2:
	a=2
else:
	a=3

for

Example:

>>> for i in range(5):
...     print i
... 
0
1
2
3
4
>>> for i in [1,2,4,5]:
...     print i
... 
1
2
4
5
>>> import random
>>> [random.randint(0,10) for i in range(5)]
[2, 5, 8, 5, 6]

try-except and raise (Exception Handling)

Example:

try:
	#something potentially bad
except:
	#catch all
    
try:
	#something potentially bad
except ExceptionClass:
	#catch ExceptionClass only

functions

• functions are objects
• functions can have multiple return types

Example:

>>> def myFc(arg1, arg2, arg3="blah"):
...     return arg1, arg2, arg3
... 
>>> print myFc(1,2)
(1, 2, 'blah')
>>> print myFc(arg1=1,arg2="hello")
(1, 'hello', 'blah')

lambda (Anonymous Functions)

• Can not contain statements

Example:

>>> increment = lambda x:x+1
>>> increment(1)
2
>>> def longFc(a,b,c,d):
...     pass
... 
>>> shortFc = lambda x,y:longFc(1,x,y,4)
>>> 
>>> myList = [1,2,3]
>>> map(lambda x:x**2,myList)
[1, 4, 9]

Sorting Lists

Example:

>>> print sorted([5, 2, 3, 1, 4])
[1, 2, 3, 4, 5]

>>> a = [5, 2, 3, 1, 4]
>>> a.sort()
>>> print a
[1, 2, 3, 4, 5]

>>> a = [5, 2, 3, 1, 4]
>>> a.sort(lambda x, y: x-y)
>>> print a
[1, 2, 3, 4, 5]

Classes

Example:

class myClass:
	def __init__(self):
    	self.classVar1 = 1
    
    def myFc(self,arg1):
    	pass
        
    def __str__(self):
    	return "myClass"

Inheritance

Example:

class derivedClass(myClass):
	def __init__(self):
    	myClass.__init__(self)

exec

• Use carefully! Potentially very insecure.

Example:

>>> python_code = "print 'hello'"
>>> exec python_code
hello

Modules and Packages

• myModule.py
• import myModule
• __init__.py

Package Structure

Example: