Python Rediscovered

7/31/2019 Python Rediscovered

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Python Rediscovered

Lecture 1


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Introduction ?

Why Python ?What can you as a user do with pythonWhat I love so much . Why I chose it .

The Calculator we all strive for ;)

The Debate of the Language style ! < DO NOT CARE > Not Compiled / Interpreted- Its a implementation

detail.

Free loosely typed scripting beauty !Open Source ! The Speed Debate ! Its every where , all platform , including Droids !Guido Van Rossum and the PEP


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Hello World and the InterpreterConsole!

print "hello world "or

print ("Hello World")

Playing with code , the beauty of an interpreter : help docs teach yourself , fool around !

Running the code the python file , and compilation USE AN IDE ! Indentation !


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The Teachers Calculator Challenge !

print(eval(input("Enter a valid expression : ")))

# exits on Ctr+C# Such lines are comments ! (''' for multiline)while True :

try :print(eval(input("Enter a valid expression : ")))except NameError :print("Enter a valid expression you twit ! ")

except KeyboardInterrupt :

exit()


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Variables and Expressions

Data Types - The New paradigm , its not an abstract world

Think of it logically, say a trip to the market !What possible things do you encounter ?

Currency -> Numbers -> Math -> Operations -> We need atype .

(note to 2.x devs : long is depreciated ) 23456789 ** 4567 is valid !

Names of things -> characters -> One More Decisions, To Do Or Not To Do THAT Is The Question

? BooleanQuantities and the List, your phonebook when you forget

what mama told you !


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Expression !Golden Rule for a Programmer #iForgot

Yes the computer is one dumb piece of shit ! BE EXPLICIT or ISTHAT SO ?

Each one of these morph depending on type ! + , -,*

/ and // ** != , ! , ^ , & , and or

Beauty of assignments in python ! a,b = b,a is VALID so is a,b,c= (110,220,130) a,b = b, a+b

type() function ! Libraries

math , cmath , numpy ..


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Interaction

Input : input () readlines() raw_input () # DEPRECATED !

Output : print ()

the formatting : Classic Style %d %s using format() format "%[padding_type][width][.[precession]]%[type]write ()


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Functions

Type()

Typecasters: int(), float(), etc. len(), sort(), sorted()Other ways of typecasting: minute/60.0Math funcs: sqrt, log, exp, etc. Composition of functions Function defintion Fruitful functions to practise:

Area of all stuff Euclidean distance

Isdivisible counting elements gcd

Recursion (Programming inception): Factorial Fibonacci


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Iteration and conditional flow

for loop range and xrange loop over lists, strings, all iterable objects nested fors

while loop nested whiles if else nested ifs break and continue and pass


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Strings - The Fortress of Python'sInvincibility

Never ever has it been easier to deal with strings - reason whyits the language of the future , AI, machine learning , NLP.String "Methods" :

ctype.h -> s.digits, .letters,.[]case , .lower(), startswith() s.find (sub) s.join # do not use '+' a list method ! s.split () s.replace() s.strip(), lstrip, rstrip

The Unicode debate ! #extars


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Lists a = [1,2,3]

b = [1,2,"asdsad"] c = [1,2,[1,2],[3,4],"sadas",(8,9)] iterating over lists appending to list - a.append("asda") list slicing indices negative index list cloning vs aliasingmatrices

Handling two dimensional lists common funcs - insert(i,x),index(x),remove(x),sort(),

reverse(), del a[0] string.split() and string.join()


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Tuples

a = (1,2,3) or just a=1,2,3 the idea behind a,b = b,a or x,y = int(x),int(y) similar to lists immutable

('a') vs ('a',) similar slicing as lists return tuples in functions


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Sets

a = [1,1,2,1,3,3] b = set(a) c = [1,1,3,4,5] d = set(c)

e = a& b (intersection) f = a|b (union) g = a-b (difference) h = a^b (symmetric difference)membership testing - "book" in ["house","book","dog"] 'z' in 'abracadabra'


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Iterators and list comprehensions

try combinations and permutations - don't return list butiterator

need to iterate over iterator to get all values the yield keyword - the intermediary return

list comprehensions - shortcut to generate lists of varioustypes of sequences

[x**2 for x in xrange(10) [(x,y) for x in [1,2] for y in [3,4] if x!= y]


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Dictionaries - We the People !

Kill the abstraction, lets name it !

Think Phonebook !

a = [xxxx,sathe,marcus]b =[123,1345,2225]what if i want a no ? b[a.index("marcus")] !!!

numbers ['marcus'] - Cool right !book = { 'marcus': 1123 , 'sathe' : { 'room' : 105, 'hometown';"bombay "}}

Sudden relavance !


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Dictionary Methods

.clear() .copy() .fromkeys(list) Using them

.get() .has_key() like the in() items() and values()

Note : iteritems/values is depreciated items is nowa iterator

.pop() .setdefault()

defaultdict(type) #example


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Looping techniques and variable args

dictionary - iteritems - for i,k in dictname.iteritems(): enumerate - lists - for k,v in enumerate(list): zip and izip - for q,a in zip(list1,list2): *args and **kwargs

def test_var_args(farg,*args):print "fomral arg",fargfor arg in args:

print "another arg:",argtest_var_args(1,"two",3,[1,2,3,4])

def test_var_kwargs(farg, **kwargs):print "formal arg:", fargfor key in kwargs:

print "another keyword arg: %s: %s" % (key, kwargs[key])test_var_kwargs(farg=1, myarg2="two", myarg3=3)

sys


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Stacks and Queues via lists

Stacks functions - append and pop

Queues need deque

from collections import deque deque list and use append and popleft queue = deque([1,2,3,4])


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Classes and Objects

Damn I Hate these slides !

Lets go a bit hands on !


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Classes and Methods

__init__(), __str__(), __repr__()others


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__str__ vs __rep__

repr - debugging representation

str - string representation and printableclass Foo:... def __str__(self):... return '__str__'... def __repr__(self):... return '__repr__'

__str__ falls back on __rep__>>> class Foo:... def __repr__(self):... return '__repr__'

>>> class Point:... def __init__(self, x, y):... self.x, self.y = x, y... def __repr__(self):... return 'Point(x=%s, y=%s)' % (self.x, self.y)


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Inheritance

class animal, dog, cat, and some other animalmethod overriding super(subclass, self).func() Base.func(self) class animal(object):

def __init__(self,name):self.name = name

def shout(self):print "I shout\n"+"I am called "+self.name

class bird(object):def __init__(self,name):

self.name = namedef chirp(self):

print "I chirp"class cat(animal):

def shout(self):animal.shout(self)print "I meow\n"+"I am called "+self.name


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Inheritance continued

class bat(animal,bird):def shout(self):

super(bat,self).shout()print "I bark\n"+"I am called "+self.name

a = animal("asd")b = bat("saddd")c = cat("sdsadad")a.shout()b.shout()c.shout()b.chirp()

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