Welcome!

Python SIG – Students with programming experience (PYA) –

Class 1 – 12-9-15

Ask doubts and give feedback

Let’s learn Python

hello world!

• The traditional first program• In Python 2:–print ‘hello world!’

• In Python 3:–print(‘hello world!’)

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]

2 vs 3

• Difference in print – statement, NOT function• Libraries, libraries, libraries

Why 2 then?

• Tools & support – 2to3, future module• Libraries, libraries, libraries. Example:

Web development• Easy to learn the other

What is code?

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]

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)

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

Python implementations

• CPython – reference implementation• Others:

PyPy – Python in Python - compiledIronPython - .NET comaptibleJython – JVM compatible

• Further reading:http://www.toptal.com/python/why-are-there-so-many-pythons

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__

Obligatory xkcd reference [5]

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

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))

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

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)

Assignment statements

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

(Important) Built-in types

• boolean• int • float• string• list• tuple• dictionary

General idea

• Flexibility in Python• Lists >> Arrays• Methods – making things simpler

Mutability

• What is it?• Why is it important?

Immutable

• int • float• string• tuple

Mutable

• list• dictionary

Operations

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

Boolean

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

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

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

In-class assignment

• Start coding!• Use help() and dir()• Use the offline docs

Thanks!

Pranav S Bijapur, ECE, BMSCE, Bangalore

b.pranavshankar@gmail.com Telegram - @pranavsb

References

1 - https://wiki.python.org/moin/Python2orPython3

2 -https://en.wikiquote.org/wiki/Martin_Fowler

3 -http://www.diveintopython.net/getting_to_know_python/everything_is_an_object.html

References

4 - https://wiki.python.org/moin/PythonImplementations

5 -https://www.xkcd.com/353/