NOTES

Declare Variables

Some Useful Functions

• print
• sys.stdout.write
• sys.stdin.readline
• bool, type
• string functions - upper, lower
• string formatting

Comments

• single line
• multi line

Datatypes

• String
• Integer
• Float
• Boolean
• Sets
• Dictionary
• Tuple
• List

Operators

• Logical: and, or, not
• Comparison Operators
• Arithmetic: +, -, *, /, // , **, enforce precedence ()

STRING

• immutable
• str yestype
• type(x)
• single quote , double quote, triple quotes
• 'a' + 4, 'a' * 3
• print() with use of \
• str.upper() and lower()
• str.split()
• string interpolation x = y + 'jain'
• float formatting and string formatting (value:width.precision)
• print('My name is rishabh {last} and I have {money:1.3f}'.format(last='jain',money=50.3145))
• from (future) import print_function

Numbers

• int, float, typecasting
• • , - , **, /, ** , //
• from decimal import Decimal as d

Boolean

• True False None

Variables

• x = 1, x = '', x = ''' '''

Lists

• mutable
• append, pop (stack)
• append, pop(0) (queue)
• insert(index, value)
• extend
• item in list
• list.join, list.sort, list.reverse
• create a list []
• add [].append()
• add list1 + list2
• slice a list
• remove from a list using .remove(value)
• new_list.sort()(In Place, returns None)
• reverse (In Place, returns None)
• sorted(), returns sorted , reversed returns iterator

Sets

• unordered collection of data
• hold unique values
• has add method
• x = set()
• you can also convert a list into a set
• Operations
  • Creation
  • Add Elements
  • Remove/Discard Elements
  • Intersection, Union, Difference, Symetric Difference, Superset/Subset

Tuples

• Create(10,)
• immutable
• Add new() = old() + (10,20)
• Unpack a tuple into multiple variables x,y,z = tupleSomething
• are like lists and preserver data integrity
• also used with print

Dictionaries

• keys are ordered in python3
• Use Immutable Keys, don't use lists
• add keys, delete keys using del
• del dict[key], del dict
• dict.pop(key)
• Keys list(dict.keys())
• key in {}
• Values list(dict.values())
• Create dicts dict(key1=10, key2=20)
• Create dicts dict([('age',10),('name','bob')])

Conditionals

• if / elif / else
• if condition: followed by indented next line
• 2 in / not in [12,20]

Ternary Operator

• x = 3 if a > b else 3

Loops

• for , while, usage of break, continue
• usage of pass in a function
• while COND: pass
• continue in the while loop to continue with the next iteration
• break to break the loop
• pass does nothing
• for var in list/tuple/dict.keys()
• iterate over a list of tuples for x,y in[(10,20),(30,40)]
• iterate over a dict for key,value in dict.items()

UserInput

• input('Enter a value')
• age = int(input("Enter Age"))

Functions

• def function_name():

• function can have return value

• args, kwargs , func_a(10, a=3)

• *args is a tuple

• **kwargs is a dictionary

• lambda

  • one line functions, annonymous functions
  • (lambda: print("hello"))()
  • x = lambda: a: a + 3, x(13)
  • age = lambda x, y: x + y, age(12,12)
  • (lambda x, y: x + y)(13,13)

• map, filter, reduce

  • map gives a gen
  • filter give a filter object
  • functools.reduce gives a value

• zip

  • returns a zip object, convert it into a list
  • returs a list of tuple of individual objects
  • zip(['a','b','c'],[10,20,30]) => [(a, 10), (b,20), (c,30)]

• file operations

  • read, write, append

• list_comprehension

  • list comprehensions to emulate map, filter
  • using ternary operators , condtions in lc

• Generators

• Decorators

• Regex

  • look for a substring within a string
  • validate a given string
  • methods in re
    • search (returns None if nothing found)
    • match (looks in the beg, returns None if nothing found)
    • split
    • findall (returns a list , [] if nothing found)
    • sub(replaceall)
  • sequence characters: \d \D \s \S \w \W \b \B
  • special characters: \ , . (any char except \n), ^, $, [A-Z][aZ][1-9] (R|R2) (R) [^g]
  • quantifiers: {m, n}, {m}, + , *, ?

Applications

• liniting: python3 -m pylint file.py

• unittest

  • functions should start with test
  • create a class that inherits unittest.TestCase
  • to run testcases use unittest.main() or python3 -m unittest file_name

• typehints

  • declaring variable type, x: int
  • declaring function return type, function(x: 4) -> int

Revision

1. NameError :if a variable does not exist

2. Conditional Operator x = 3 if 3 > 2 else 5

3. print("abc", end="\n")

4. Boolean Values: True/ False Everything has a boolean value bool(0), bool(-1)

5. Conditional Opearators: and, or, not

6. Comparison Operators: ==, !=, <=, >=

   1 < 2 and 2 < 3 is same as 1 < 2 < 3

7. a is b # True i.e a and b are the same object e.g a = [1,2,3] b=a

8. a == b # True i.e a is equal to b in value

9. Comments: #, """ """,

10. Numbers: int, float, /, // , 2 ** 3, enforce precedence (1 + 2) * 3

11. Strings, immutable, Slice, Step Size, String formatting, upper, lower, count,
    (Note: is None == None, almost does the same thing)

12. Sets , create a set, add element, discard element intersection, union, difference, symetric difference, discard/remove subset/superset <=, >=

13. Dictionary, keys should be immutable, keys can be strings, ints, floats , tuples Use x.get('key') Dictionary Expansion y = {"a": 10, **b} from collections import OrderedDict list(x.keys()), x.values(), x.items()

14. Lists are mutable l.append(5) l.pop() l.pop(0) l.insert(0,10) l.extend(b) in operator in lists

15. tuples are good for unpacking a, b = 2, 3 a, *b, c = [1,2,3,4,5]

16. Conditionals if , elif , else

17. Loops: for, while, break, continue using pass

18. function, documentation inside function arguments, and keyword arguments lambda expression map, filter, reduce, zip, zip + list, zip + list + dict enumerate, min, max function scope: L,E,G, B

19. List Comprehension LC with conditions (if / else) Generator Expression with LC Set Comprehension Dict Comprehension

20. Decorators Higher Order Function

21. Generator, yield keyword, lists /iterators, iter function on list , next function

22. File Operations using with to open files and perform read write and append

23. Exception Handling assert raise try/except/else/finally, print exception name custom excepotion

24. Classes

    • Class Variables
    • Instance Variables
    • Class Methods
    • Static Method
    • Regular Methods
    • Method Overloading
    • Private Vairables
    • Private Method
      • (How can private be not so private)
    • Magic Methods(str, del, len, )
    • Doc String Inside Classes/ Doc String Inside Methods

    Data Hiding

    • abstraction
    • encapsulation

    Polymorphism