Python 3 Programming

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Python

Introduction to Python

Python is a high-level, interpreted, interactive and object-oriented scripting language which finds its application in many areas like –

  • Webscripting
  • 3d Modelling (Blender)
  • Desktop Applications – Games (Pygame)
  • Scientific usage (SciPy/NumPy)

Python source code is available under the GNU General Public License (GPL). There are two major Python versions, Python 2 and Python 3.

Python features

Python Common Features

  • Open Source and Simple to use
  • Very powerful and Ubiquitous
  • Supports broad standard library
  • Supports interactive testing and debugging
  • Established interface with all major DB’s
  • Runs on variety of hardware platforms

Technical features of Python

  • Object-oriented (supports both functional and structured programming)
  • Dynamically and strongly typed
  • Whitespace delimited (Indentation)
  • Scripting language which supports large applications.
  • High-level dynamic data types and supports dynamic type checking
  • Automatic garbage collection
  • Interpreted makes compiler interact with developer.
  • Easy integration with C, C++, COM, ActiveX, CORBA and Java.

Python Implementations

  • CPython – Python implementation on standard C language.
  • Jython – Python implementation with Java virtual machine to blend with Java.
  • Pypy – Python implemented in Python and its Just-in time compiler making it fastest.
  • Iron Python – for windows, which implements common runtime libraries to interface with .NET.

Difference between Python2 & Python3

Python versions

  • Two main Python current versions
  • At the time of this writing: 2.7.14 and 3.6.4
  • Small but significant differences

Python 2

  • Is still in current use
  • Will be moved to maintenance after its final release 2.7.x
  • Some updates from Python 3.x have been backported to 2.7
  • Not fully compatible with Python 3

Python 3

  • Intentionally broke compatibility with 2.x in order to make things better
  • Most modules have now been updated with 3.x versions
  • Should be the default for any new project you start

Reasons to Use Python 3

  • From Python.org: “Short version : Python 2.x is legacy, Python 3.x is the present future of the language”
  • Unless you need a 2.x module, use Python 3

Some sample differences:

Print:

  • Python 2 treats “print” as statement rather a function.
  • Python 3 explicitly treats “print” as a function.

Integer Division:

  • Python 2 treats numbers without any digits. (Output of expression 3 / 2 is 1, not 1.5). To get the result 1.5, you would have to write 3.0 / 2.0.
  • Python 3 evaluates 3 / 2 as 1.5 by default, which is more intuitive for new programmers.

List Comprehension Loop Variables: Common name for the variables that is iterated over in a list comprehension as a global variable get interchanged. This is fixed in Python 3.
Unicode Strings: By default Python 3 stores strings as Unicode unlike Python 2.
Raising Exceptions: Python 3 requires different syntax for raising exceptions.

  • Python 2:raise IOError, “some error message”
  • Python3: raise IOError(“some error message”)

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