Python Notes.txt

============================================ DAY 1 =============================================================================

-> Programming language : which has decision making power (DMP) --> ctrl structure --> (if else loop or while loop, etc).

-> library : collection of predefined functions or objects or classes.

-> framework : it provides some rule and design pattern.
   Design patterns : MVC, MVT, MVVC

-> functions : 1. outside classes
	           2. syntax : fun_name()

-> methods : 1. inside classes
             2. syntax : something.method_name()

-> why python : 1. Larger community
		2. more libraries
		3. multi domain (it can be used in web dev, ML, AI, etc)

-> programming languages has 3 structures :
	1. functional : c lang
	2. oop : java, c#
	3. hybrid : python, js

-> There are 3 data types:
	1. static : int num = 10; --> java, c ++
	2. dynamic : num = 10 or num = 'Fynd' --> python, js
	3. hybrid : groovy lang

-> Dynamic lang are slower than static lang

-> How code executes in python :
	1. PVM stands for python virtual machine which contains compiler and interpreter
	2. source code goes to compiler then compiler convert it to machine code (.class file) which contains byte code
	3. Further Byte code goes to interpreter and interpreter executes it line by line.

-> Flavours of python ( different kind of compilers in python) :
	1. PYPY --> python ( faster among all compiler)
	2. Iron Python --> dotnet
	3. CPython --> c lang (default compiler of python)
	4. JPython --> java lang 

=============================================== DAY 2 ==========================================================================

-> Memory Management :

	1. shell : int --> -5 to 256 (small integer caching concept) --> same address will be allocated
		   float --> differ on delimeters 
		   string --> same address will be allocated
	
	2. IDE or editor (demo.py) : int --> same
								 float --> same
								 string --> same


-> strings : strings.py


Questions :

1. 
x = 1000
y = 2000

print(id(x))
print(id(y))

x = 999
print(id(x)) 
print(id(y))

what happens to x = 1000 after we assign x = 999 ?


2. 

x = 1000
x = 2000

print(id(x))
print(id(y))

if we create two same variable in python why it is working and not giving error ? 


3.

str1 = "Fynd"

print(id(str1))
print(id(str1[0]))

why str1 and str1[0] base address is not same ?


===================================================== DAY 3 =====================================================================

Solution of above 3 Questions :

1. 
x = 1000
y = 2000

print(id(x))
print(id(y))

x = 999
print(id(x)) 
print(id(y))

what happens to x = 1000 after we assign x = 999 ?

Ans :
-> when we assign x = 1000 it creates object of int class for value 1000 and store it in heap memory and the address of 1000 is stored in x.
-> variable x and address of 1000 is stored in global memory in form of key value pair in dictionary.
-> when again we assign x = 999 then it creates another object of int class for value 999 and store it in heap memory.
-> now as we know in dictionary we cannot create same key thats why address of 1000 value will overwrite and x will hold the address of 999 and x will start pointing to address of 999.
-> reference collector will remove the connection between x and address of 1000 further address of 1000 value will be discarded.
-> now 1000 value is without address so garbage collector will remove the 1000 value from heap memory.

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2. 

x = 1000
x = 2000

print(id(x))
print(id(y))

if we create two same variable in python why it is working and not giving error ? 

Ans:

-> when we assign x = 1000 it creates object of int class for value 1000 and store it in heap memory and the address of 1000 is stored in x.
-> variable x and address of 1000 is stored in global memory in form of key value pair in dictionary.
-> when again we assign x = 2000 then it creates another object of int class for value 2000 and store it in heap memory.
-> now as we know in dictionary we cannot create same key thats why address of 1000 value will discarded and x will hold the address of 2000 and x will start pointing to address of 2000 that's why in python does not give error above problem statement.

-------------------------------------------------------------------------------------------------------------------------------------------

3.

str1 = "Fynd"

print(id(str1))
print(id(str1[0]))

why str1 and str1[0] base address is not same ?

Ans :

-> When we assign str1 = "Fynd" it creates object of string class and store it at some memory address in which all substring addresses are stored w.r.t. indexes.
-> All substring addresses points to substrings which are stored in heap memory. This is reason when we check address of str1 and str1[0] we get different memory addresses.

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# Array indexing concept :

-> In array, indexing works on base address + offset(displacement) and not on logical indexing that we see in programming i.e. 0,1,2,...
# Base Address : the address at which object is stored.
# offset (displacement) : the integer value indicating distance between the beginning of object and the given element or point.

for e.g. :

arr = [10,34,45,6]  

suppose, address of 10 is AD1234

then the address of 34 will be AD1234 (base address) + 4 (offset) => AD1238
address of 34 is AD1238

This is how internally array indexing works.
 
========================================================== DAY 4 ===========================================================================

List --> List.py

Tuple --> Tuple.py

========================================================== DAY 5 ===========================================================================

Dict_29_05_23.py

Set_29_05_23.py

========================================================= DAY 6 ============================================================================

Control_Structure_30_05-23.py

========================================================= DAY 7 ============================================================================

Functions_31_05_23.py

========================================================= DAY 8 to 18 ============================================================================

OOP_08_to_18.py

========================================================= DAY 19 ===========================================================================

Exception_Handling_15_06_23.py