print(False == 0) # True
    print(True == 1) # True

    print(True + True + True) # 3
    print(True + False + False) # 1

    print(None == 0) # False
    print(None == []) # False

    # bool(empty variable, None, 0, null) = False
    print(bool("hi")) # True
    print(bool(0)) # False
    print(bool("")) # False
    print(bool([])) # False
        

    print("a" in "apple") # True
    for i in "apple":
        print(i) # "a", "p", "p", "l", "e"
    print(' ' is ' ') # True: string is immutable
    print({} is {}) # False: dictionary is mutable
        

    def fun():
        S = 0
        for i in range(10):
            S += i
        return S
    print(fun()) # 45

    def fun():
        S = 0
        for i in range(10):
            S += i
            yield S
    for i in fun():
        print(i) # 0, 1, 3, 6, 10, 15, 21, 28, 36, 45
        

    ''' accessing local variable in global scope '''
    def f():
        s = "abc"
        print("Hi", s) # Hi abc
    f()
    print(s) # NameError: name 's' is not defined

    ''' local variable with same name as that of global variable '''
    def f():
        s = "Hello"
        print(s) # Hello
    s = "Hi there"
    f()
    print(s) # Hi there

    ''' trying to access global variable in local scope '''
    def f():
        s += " there" # UnboundLocalError: local variable 's' referenced before assignment
        print("Inside Function", s)
    s = "Hi"
    f()

    ''' accessing global variable in local scope using global keyword '''
    def f():
        global s
        s += ' there'
        print(s) # Hi there
        s = "Hello"
        print(s) # Hello
    s = "Hi"
    f()
    print(s) # Hello

    ''' global keyword '''
    a = 1
    def f(): # Uses global because there is no local 'a'
        print(a) # 1
    def g(): # Variable 'a' is redefined as a local
        a = 2
        print(a) # 2
    def h(): # Uses global keyword to modify global 'a'
        global a
        a = 3
        print(a) # 3
    print(a) # 1
    f()
    print(a) # 1
    g()
    print(a) # 1
    h()
    print(a) # 3

    ''' global in nested functions '''
    def add():
        x = 15
        def change():
            global x
            x = 20
        print(x) # 15
        change()
        print(x) # 15
    add()
    print(x) # 20
        

    # global variable
    x = 15

    # nonlocal keyword
    def fun():
      var1 = 25
      def gun():
        nonlocal var1 # tells python explicitly to use var1 initialize in fun()
        global x # tells python explicitly to use x initialized globally
        var1 = var1 + x
        print(var1) # 40
      gun()
    fun()
        

What is the difference between == and is == compares the values of both the operands and checks for value equality. Whereas the is operator checks whether both the operands refer to the same object or not (present in the same memory location)

    list1 = []
    list2 = []
    list3=list1
    print(list1 == list2)      # True
    print(list1 is list2)      # False
    print(list1 is list3)      # True
    list3 = list3 + list2
    print(list1 is list3)      # False
        

What are some ways to remove duplicates from a list?

    l1 = ["a", "b", "c", "a", 1, 3, 3, 5]
    ''' using a set '''
    l2 = list(set(l1))
    ''' using keys in a dictionary '''
    l3 = list(dict.fromkeys(l1))
        

    f = [1,2,3,4]
    s = f
    s.append(5)
    print(s) # [1,2,3,4,5]
    print(f) # [1,2,3,4,5]
        

    from random import shuffle
    f = [1,2,3,4]
    shuffle(f) # shuffle values in f into a random order
        

    print(5//2) # 2
    print(-5//2) # -3
    print(5//-2) # -3
    print(5.0//2) # 2.0
    print(-5.0//2) # -3.0
    print(5.0//-2) # -3.0
        

    l1 = [1,2,3,4,5]
    print(l1 * 2) # [1,2,3,4,5,1,2,3,4,5]
        

    x, y, z = 1, 2
    print(x, y, z)  # ValueError: not enough values to unpack (expected 3, got 2)
        

• The nonlocal keyword is used to work with variables inside nested functions, where the variable should not belong to the inner function
• Use nonlocal to declare that the variable is not local to the nested function, allowing you to modify the variable's value in the enclosing scope.

    def outer():
        x = "local"
        def inner():
            nonlocal x
            x = "nonlocal"
            print("Inner:", x)

        inner()
        print("Outer:", x)

    outer()               # Inner: nonlocal \n Outer: nonlocal