This document serves as an introduction to Python programming, distinguishing between Python versions 2 and 3, and emphasizing the importance of code readability and understanding. It covers essential concepts like objects, data types, import mechanisms, and provides insights into Python's dynamic and interpreted nature. Additionally, it encourages learners to explore documentation and start coding as part of the learning process.

1. Welcome!
Python SIG – Students with
programming experience (PYA) –
Class 1 – 12-9-15

2. Ask doubts and give feedback

3. Let’s learn Python

4. hello world!
• The traditional first program
• In Python 2:
–print ‘hello world!’
• In Python 3:
–print(‘hello world!’)

5. 2 vs 3
• 2.7 last in 2 series
• 3 under development
• Ultimately, not much difference
• “The most drastic improvement is
the better Unicode support (with all
text strings being Unicode by
default)” [1]

6. 2 vs 3
• Difference in print – statement,
NOT function
• Libraries, libraries, libraries

7. Why 2 then?
• Tools & support – 2to3, future
module
• Libraries, libraries, libraries. Example:
Web development
• Easy to learn the other

8. What is code?

9. What is code?
• Any fool can write code that a computer can
understand. Good programmers write code
that humans can understand.
Martin Fowler, "Refactoring: Improving the
Design of Existing Code" [2]

10. Objects, objects everywhere!
• “Everything in Python is an object, and almost
everything has attributes and methods. All
functions have a built-in attribute __doc__,
which returns the doc string defined in the
function's source code.” [3]
From Dive Into Python by Mark Pilgrim
• help(int)

11. Python implementations
• Language and implementation – separate
issues
• Language == syntax
• “An "implementation" of Python should be
taken to mean a program or environment
which provides support for the execution of
programs written in the Python language” [4]
From wiki.python.org

12. Python implementations
• CPython – reference implementation
• Others:
PyPy – Python in Python - compiled
IronPython - .NET comaptible
Jython – JVM compatible
• Further reading:
http://www.toptal.com/python/why-are-
there-so-many-pythons

13. CPython
• Interpreted; with “bytecode” in between (like
Java)
• C heritage
• Examples:
– Can use numbers as boolean types; though a
separate boolean type exists
– __name__ == __main__

14. Obligatory xkcd reference [5]

15. Explaining the comic - why Python
is awesome
• Dynamic vs static typing
• Whitespace as indentation
• Strongly typed vs weakly typed languages
• REPLs – rapid prototyping
• Interpreted – line by line; easier to find errors

16. import - ing
• Libraries and packages
• Batteries included philosophy of Python
• import antigravity
• import this
• import lotsofotherawesomestuff
• import modulename (BTW, modules (== .py files))
• from modulename import methodname
(BTW, methods ((not exactly) == functions))

17. Python is just words
• and del from not while as elif global or with
assert else if pass yield break except import
print class exec in raise continue finally is
return def for lambda try
• + variables
• + structure that you create

18. User input
• Complex programs = input + efficient
computation + output
• raw_input, NOT input
• raw_input – reads as string, so convert when
required (strongly typed, remember?)
• Example:
– var = raw_input(prompt)

19. Assignment statements
• Assignment is =
• ( and equality is ==, but you know this right?)
• Variable names should be sensible
• varname = computation / input
• Depends on frame

20. (Important) Built-in types
• boolean
• int
• float
• string
• list
• tuple
• dictionary

21. General idea
• Flexibility in Python
• Lists >> Arrays
• Methods – making things simpler

22. Mutability
• What is it?
• Why is it important?

23. Immutable
• int
• float
• string
• tuple

24. Mutable
• list
• dictionary

25. Operations
• + - * / % and ** for exponentiation
• Also +=, -=, *=, /=
• Floating point arithmetic
– [int].0
– Or float()

26. Boolean
• True / False
• >
• <
• ==
• !=
• >=
• <=
• is , is not (same as id())

27. Strings
• Immutable
• Single or double, they don’t care
• Raw strings
• Escape sequences
• String slicing – string[start:stop:step]
• We count from 0 (why?)
• String methods

28. Read the documentation
• If you know programming, (which you say you
do) reading the documentation is the best way
to learn
• Don’t have to memorise, only know how to
find what you need

29. In-class assignment
• Start coding!
• Use help() and dir()
• Use the offline docs

30. Thanks!
Pranav S Bijapur,
ECE, BMSCE, Bangalore
b.pranavshankar@gmail.com
Telegram - @pranavsb

31. References
1 -
https://wiki.python.org/moin/Python2orPyth
on3
2 -
https://en.wikiquote.org/wiki/Martin_Fowler
3 -
http://www.diveintopython.net/getting_to_kn
ow_python/everything_is_an_object.html

32. References
4 -
https://wiki.python.org/moin/PythonImpleme
ntations
5 -
https://www.xkcd.com/353/