Python Basic

##short hand if-else
a=1
b=3
print("hello") if a>b else print("Bye")

##DocStrings
def fun():
    """ This function does nothing and 
    this is docstring that gives info about fun work"""

print(fun.__doc__)


##Dealing with file

read mode
f=open("first.txt")
content=f.read()
print(content)

write mode -- overrides the previous content
f=open("first.txt","w")
f.write("Srushti")

append mode --appends to the  previous content
f=open("first.txt","a")
f.write("Srushti Hello")

read+write mode 
f=open("first.txt","r+")
content=f.read()#reads complete text in file
f.write("Good Morning and Welcome to fresh morning")
# content=f.read(3)#reads upto 3 characters in file
print(content)
content=f.read(3)
print(content)
f.close()

readline
f=open("first.txt")
# print(f.readline())
# print(f.readlines())

c=f.read()
for line in c:
    print(line,end='')

tell()-- tells where our pointer is
seek()--takes the pointer back to 
f=open("first.txt")
print(f.tell())
print(f.readline())
print(f.tell())
f.seek(10)
print(f.tell())
print(f.readline())
print(f.tell())
f.close()

##with block
with open("first.txt") as f:
    a=f.read()
    print(a)
f=open("first.txt")
print(f.readline())

##global keyword
l=10
def fun():
    l=9
    global m
    m=7
    print(l)
    print(m)
fun()
print(l)
print(m)
x=8
def fun():
    x=30
    def gun():
        global x
        print("Global ",x)#8
        x=9
        print("Global changed",x)#9
    gun()
    print("fun()",x)#30
fun()
print("Changed global",x)# 9

##randint
import random
print(random.randint(0,19))
print(random.random())
l=[1,2,3,4,"hello"]
print(random.choice(l))

##string format
s="helloj"
a=2
a2="this is formatting %s %s"%(s,a)
a3=f"this is also {s} formatting{a}"
a4="this is{} {}"
a4=a2.format(s,a)
print(a4)
print(a2,a3)


##variable arguments

def fun(n,*args):
    print(n)
    print(type(args))
    return args
l=["hello","kello"]
n="yess"
# print(n,fun(*l))   #mystery
# print(fun(*l),n)#error
print(fun(n,*l))


def fun(*args,**args2):
    for item in args:
        print(item)
    for i,j in args2.items():
        print(i,j)
l=["hello","world"]
l2={"kilo":"weight","banana":"fruit"}
fun(*l,**l2)

##time module to check time taken by program
import time
i=time.time()
print(i)
j=0
k=0
while j<5:
    j=j+1
    time.sleep(1)
    print("Hello")
print(time.time()-i)
i=time.time()
while k<5:
    k=k+1
    print("Hello")

print(time.time()-i)
localtime=time.asctime(time.localtime(time.time()))
print(localtime)


##import
import sys
print(sys.path)
from pattern import a
print(a)

import pattern
print(pattern.a)
""" run the pattern program and the output would be And the main is pattern"""
if __name__=='__main__':
    print("h")

##map
l=["1","3","4"]
print(l)
l2=list(map(int,l))# map(what to perform,on what)
print(l2)
def square(a):
    return a*a
def cube(a):return a*a*a
fun=[square,cube]
for i in range(0,5):
    l2=list(map(lambda x:x(i),fun))
    print(l2)


##filter

l=[1,2,3,4]
# l2=list(map(lambda x:x<3,l))
l2=list(filter(lambda x:x<3,l))

print(l2)

##reduce
from functools import reduce
l=[1,2,3,65]
l2=reduce(lambda x,y:y+x,l)
print(l2)

#dealing with functions deletion
def fun():
    """ fun still works even if we delete it b'coz it is always saved"""
    print("It still works")

print(fun.__doc__)
gun=fun
del fun
gun()

##function within function
def f(a):
    if(f==0):
        return print
    else:
        # return int
        return sum
print(f(0))
print(f(1))

def fun(gun):
    gun("This gun is printed")
fun(print)

##decorator
def f(gun):
    def exe():
        print("Executing")
        gun()
        print("executed")
    return exe
    
@f
def who():
    print("it's a decorator")
# who=f(who)  # another way to use it as a decorator is @function name
who()


##OOPS STARTED

class Emp:
    n=3
    """ this is the doc of Emp class"""
em=Emp()
em2=Emp()
print(em2.n)#n is class variable
em.n=8
print(em2.n)#3
print(em.n)#8
Emp.n=9#change the class variables with class name only
print(em2.n)#9
print(em.n)#still 8
em.name="fan"
em2.name="fan2"
print(em.__dict__)
print(Emp.__dict__)

##class methods  ---- used to change class variables for class and all its instances

class s:
    n=9
    @classmethod
    def fun(cls,n):
        cls.n=n
f=s()
g=s()
f.fun(89)
print(s.n)

##class methods as alternative constructor

class s:
    def __init__(self,name,id):
        self.name=name
        print("Constructor called")
        self.id=id
    @classmethod
    def convert(cls,string):#alternative constructor
        p=string.split("-")
        return cls(p[0],p[1])
        return cls(*string.split("-"))

    @staticmethod
    def junk(a):
        print(f"{a} is a junk food")
        return "No"


print(s.junk("Sandwich"))
# s1=s("sam",88)
# s2=s("tom",34)
# s3=s.convert("tomcat-23")
# print(s1.name)
# print(s3.name)

#Inheritance
##Single inheritance
class Emp:
    salary=230876
    name="Meena"
    time=45
    def __init__(self,name,salary,t):
        print("Employee constructor")
        self.name=name
        self.salary=salary
        self.time=t
    def work(self):
        print(f"{self.name} worked for {self.time} hrs")
    
    def salary2(self):
        print(f"Salary of {self.name} is {self.salary} ")
e=Emp("Srushti",10000000,354)
e.work()
e.salary2()

class Programmer(Emp):
    lang="Python"
    def __init__(self,name,salary,t,lang):
        # Emp.__init__(self,name,salary,t)
        super().__init__(name,salary,t)
        self.lang=lang
        print("Programmer constructor")
    def printAll(self):
        print(f"Name : {self.name}\nSalary : {self.salary} \nWork Time : {self.time} \nLanguage : {self.lang}")
p=Programmer("Larry",347974,47,"Java")
p.printAll()


##multiple inheritance
class Emp:
    def p(self):
        print("f() of Emp")
class Pro:
    def p(self):
        print("p() of Pro")
class Per(Emp,Pro):
    pass
p=Per()
p.p()

multilevel 
class Emp:
    def p(self):
        print("f() of Emp")
class Pro(Emp):
    def p(self):
        print("p() of Pro")
class Per(Pro):
    pass
p=Per()
p.p()

private=__variablename,public=variablename,protected=_variablename
class E:
    n=2
    _n=9
    __n=8
e=E()
print(e.n)
print(e._n)
print(e._E__n)#private variable is called like this

########Very imp

class A:
    var1="I am a class variable in class A"
    def __init__(self):
        self.var1="I am an instance variable in class A"
class B(A):
    var1="I am a class variable in class B"
    def __init__(self):
        self.var1="I am an instance variable in class B"
a=A()
b=B()
print(b.var1)

#check for instance variable in class B---> 
#if not then goes for instance variable of A--->
#if not then goes for class variable of class B--->
#if not then goes for class variable of A--->
#if not then gives error


##operator overloading using dunder methods
class Emp:
    def __init__(self,salary):
        self.salary=salary
    def __add__(self,other):
        return self.salary+other.salary
    def __truediv__(self,other):
        return self.salary/other.salary
    def __repr__(self):
        return f"{self.salary} from repr since str is not present" 
    #without repr the output was <__main__.Emp object at 0x0000024156FC92B0>
    def __str__(self):
        return f"{self.salary} from str"

e=Emp(12)
e2=Emp(34)
print(e+e2)
print(e/e2)
print(e)