Networking, Python, BigData and Linux

from enum import IntEnum, Enum, unique import sys sys.stdout = open(__name__, 'w') class CountryCode1(Enum): Nepal = 977 India = 91 Pakistan = 92 Bangaladesh = 90 Bhutan = 93 Bhutan = 90 class CountryCode2(IntEnum): Nepal = 977 India = 91 Pakistan = 92 Bangaladesh = 90 Bhutan = 93 Bhutan = 90 def test_countryCode_1(): for i in CountryCode1: print ( "With enum Inherited from Enum => Country : {}, Code : {}" .format(i.name, i.value)) def test_countryCode_2(): try : for i in sorted (CountryCode1): print ( "With enum Inherited from Enum & Trying to Sort Enum Object => Country : {}, Code : {}" .format(i.name, i.value)) except Exception as e: print ( "With enum Inherited from Enum & Trying to Sort Enum Object: {}" .format(e)) de

Generators are very powerful in Python. Its created using 'yield' within the function. Here are three most important variants, where 'yield' makes a function a generator, a coroutine or  as a context manager: [Will explain each when i get time :) ] A. Using 'Yield' as a generator in function: def mygen(a=0, b=1):   while True:        yield b        a, b = b, a + b  c = mygen()  for i in range(10): print(c.next()) B. Using 'Yield' as co-routine: def mycoroutine():       v_count = 0 inv_count = 0      try:           while True:                   myinput = yield                  if isinstance(myinput, int):                          v_count = v_count + 1                  else:                          inv_count = inv_count + 1        except GeneratorExit:               print("You Sent {} valid digits and {} invalid chars:".format(v_count,inv_count))   mygen = mycoroutine()  mygen.next() for i in range(

Lets consider the following python code: class A: def do(self): print("From the class: A") class B(A): def do(self): print("From the class: B") class C(A): def do(self): print("From the class: C") class D(C): pass class E(D, B): pass class F(E): pass What would be the output of following? inst= F() inst.do() Well, to understand this we should know the method resolution order in python's inherited classes. In Python 2.x, the resolution algorithm is: Search Deep first & then Left to Right order. That is In above example, the Order would be F->E->D->C->A->B-A So the output will be : From the class: C However, In Python 3.x, the resolution algorithm is: Left to Right first & Deep. That is in above example the resolution order will be : F->E->D->B->C->A So the output will be : From the class: B For Details, refer to : https://en.wikipedia.org/wiki/C3_linearization

Memory Management in Python: 'Important points' Dynamic Allocation(on Heap Memory) -> Objects and values  Stack Memory => variables and Methods/Functions Everything in Python is object.  Python always uses heap to store the Ints, String values etc unlike the C. It maintains the reference counts if multiple variables are pointing to the same Objects. However for weak-refs the refcount is not incremented. Once the Reference count(sys.refcount=0) reaches zero python does Automatic Garbage collection immediately.  Refcounts are not thread safe.  The main reason GIL comes into play.  In Class, we can use __slot__ = ('x','y') etc to make the class immutable i.e not to allow to have new attributes/methods. In Complex data structure such as doubly LinkedList, DeQueue, Trees; in some cases due to cyclical references, Ref counts never reaches to Zero. In that case, Python uses Mark & sweep(Java Uses) Algorithm periodically by marking the only objec

What happens during Linux boot process ? Read here: https://www.thegeekstuff.com/2011/02/linux-boot-process What happens during the Login by  Non-privileged user post reboot? Init process (pid=1, uid =0 ) spwans the Login process  (pid-x,uid=0)   Fork() system call   Exec system call Login Process  Fork() System Call setuid for the User (pid x, uid=0) Exec System call  Shell Uid >0, PID x Execute ~/.bashrc ; exports all the enviornment variables etc/

Python has powerful exception handling capabilities. There are few exception which are present in BaseException class, and many exceptions are derived from the class Exception which is the child class of BaseException. All the user defined exceptions has to be derived from the class class Exception or its child. Let's see exception SystemExit direct child of BaseException in action: import sys try: sys.exit() except Exception as e: pass print(e) In above case, the program exits regardless of Exception being caught. That is because, System exit exception is derived from BaseException not Exception. However, in following case; the exception is caught as expected: import sys try: sys.exit() except BaseException as e: pass print(e) # o/p -> 'SystemExit' Lets' see few awful things that can go wrong in Exceptions try/catch: try: raise "Value Error" except "Value Error": pass print("UnCaught!") # TypeError: exce

Lets say, in python list a= [ 1 , 1 , 2 ] . Ever wondered how the memory allocation would happen in Python for the list elements ? In Python, the variables are tagged, meaning the elements of above list 1,1 would be stored in the same location and 2 is stored in different location. when we print the memory location of a i.e id(a) and  memory location of each elements , we get the results. (4315182216, 140602806130168, 1) (4315182216, 140602806130168, 1) (4315182216, 140602806130144, 2) As seen above the memory address of a = 4315182216, memory address of 1 is 140602806130168 for first and second elements. Now, to see more understanding and impacts of above such memory allocation, we see the various ways of copying the list, and check the impact on copied list due to modification on the original list variable or list elements. ::Without using Copy Module::: i.e when b = a ----------------------------------------Memory addresses of List a, before modification on a:------

Serialisation and DeSerialisation a.k.a SerDe are the important aspects of streaming data into file from objects and from the file to objects. There are many ways in Pythons to do so. Few of the tools are PyYaml, JSON and cPickle. However, cPickle is the fastest as it can SerDe any python objects such as Strings/texts, Lists, Dicts, Class obj in the byte formats. One thing to worry about the SerDe such as cPickle is that, the security is a great concern if we store the objects information as byte stream into the file. Hence, cPickle should be used carefully with the highest possible protocol.Following Example, demonstrates the serDe with cPickle for Python class Objects. import cPickle  class acc:     def __init__(self, id, bal):    self.id = id     self.bal = bal    def dep(self, amount):       self.bal += amount   def withdraw(self, amount):      self.bal -= amount ac = acc('1988999', 200)  ac.dep(1000)  ac.withdraw(500)  fd = open("ty2&q

# Lets define a class with some methods as: class Nums: def __init__ ( self , n): self .val = n def multwo( self ): self .val *= 2 def addtwo( self ): self .val += 2 def devidetwo( self ): self .val /= 2 # Lets create the instance of the class: f = Nums( 2 ) Now, call each and every methods as in dir(f) list. You should however, take care of methods taking arguments. Example, for init we need to pass args. for m in dir (f): mymethod = getattr (f, m) if callable (mymethod): if 'init' not in str (mymethod): mymethod() else : pass print (f.val) => It results 4. Wonder why ?  To figure out, lets see in which order the methods within the class are invoked: This is how the instance stores the methods and properties lists: ['__doc__', '__init__', '__module__', 'addtwo', 'devidetwo', 'multwo', 'val'] So, val = (2+2)/

In Python, there is nothing like data hiding. However, we can have representation of data hiding with _(single Underscore). __(Double Underscore) Means the methods and properties can't be overridden in derived classes. Trying to do show causes exceptions. @abstractmethod   Decorator   on any methods mean, that should be   overridden for sure in derived class. Not implementing that method causes exceptions. __xyz__ (Double Underscore prefix and suffix) Means the method/attribute is an builtin, can be overridden.  Example:  from abc import ABC, abstractmethod class Base(ABC):       def __init__(self):                   self.result = self._private()       def  _private (self):         return "Yes"       @ abstractmethod        def you_should_override(self):             pass      def __you_cant_override(self):             pass class Derived(Base):            def you_should_override(self):             pass        

P ython data models are important aspects in designing the objects.   Python data models helps you to implement how your objects should behave to the user. Example: By Default, print(object) prints non-useful o/p, we can make it to produce something meaningful to the user.   This experiment, tries to implement few DataModels for LinkList object in Python such as iter(Makes linkedList Object iterable), eq(Compares Two LinkedLists on  == operator), add(Adds Elements of two LinkedLists), str(Prints the elements of LinkList on printing the object), repr(Display the representation of LinkedList object on repr method) etc. For Implementation details, please visit the git Link: https://github.com/Indu-sharma/Utilities/tree/master/Python_generic/PythonDataModels

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