# Loops In Python (for, while loop) Example 1: ```python # For loop statement # It has the ability to iterate over the items of any sequence, such as a list or a string. # Syntax # for iterating_var in sequence: # statements(s) # If a sequence contains an expression list, it is evaluated first. # Then, the first item in the sequence is assigned to the iterating variable iterating_var. # Next, the statements block is executed. Each item in the list is assigned to iterating_var, and the statement(s) block is executed until the entire sequence is exhausted. #Examples s = 'PYTHON' for x in s : print(x) ``` P Y T H O N Example 2: ```python # It can be used to iterate over iterators and a range. # Iterating over a list print("List Iteration") l = ["books", "bags", "pens"] for i in l: print(i) ``` List Iteration books bags pens Example 3: ```python # Iterating over a String print("\nString Iteration") s = "Python_is_awesome" for i in s : print(i) #String Iteration ``` String Iteration P y t h o n \_ i s *\_* a w e s o m e Example 4: ```python # Iterating over dictionary print("\nDictionary Iteration") d = dict() d['xyz'] = 123 d['abc'] = 345 for i in d : print("%s %d" %(i, d[i])) ``` Dictionary Iteration xyz 123 abc 345 Example 5: ```python # One parameter for i in range(5): print(i) ``` 0 1 2 3 4 ## Practice problems: Example 6: ```python # Two parameters for i in range(3, 6): print(i) ``` 3 4 5 Example 7: ```python # Three parameters for i in range(4, 10, 2): print(i) ``` 4 6 8 Example 8: ```python # Going backwards for i in range(0, -10, -2): print(i) ``` 0 -2 -4 -6 -8 Example 9: ```python i = 0 while i < 3: print(i) i += 1 else: print(0) ``` 0 1 2 0 Example 10: ```python my_string = "Python" i = "i" while i in my_string: #No output why? print(i, end =" ") ``` No Output Example 11: ```python my_string = 'Python is Awesome' for i in range(my_string): print(i) ``` TypeError Traceback (most recent call last) in () 1 my\_string = 'Python is Awesome' ----> 2 for i in range(my\_string): 3 print(i) TypeError: 'str' object cannot be interpreted as an integer Example 12: ```python my_string = 'We love Python' for i in range(len(my_string)): print(my_string[i].upper()) ``` W E L O V E P Y T H O N Example 13: ```python my_list = ['one', 'two', 'three', 'four', 'five'] my_list_len = len(my_list) for i in range(0, my_list_len): print(my_list[i]) ``` one two three four five Example 14: ```python for i in range(5, 0, -1): if i == 1: print('1 bottle of beer on the wall, 1 bottle of beer!') print('So take it down, pass it around, no more bottles of beer on the wall!') elif i == 2: print('2 more bottles of beer on the wall, 2 more bottles of beer!') print('So take one down, pass it around, 1 more bottle of beer on the wall!') else: print('{0} bottles of beer on the wall, {0} bottles of beer!'.format(i)) print('So take it down, pass it around, {0} more bottles of beer on the wall!'.format(i - 1)) ``` 5 bottles of beer on the wall, 5 bottles of beer! So take it down, pass it around, 4 more bottles of beer on the wall! 4 bottles of beer on the wall, 4 bottles of beer! So take it down, pass it around, 3 more bottles of beer on the wall! 3 bottles of beer on the wall, 3 bottles of beer! So take it down, pass it around, 2 more bottles of beer on the wall! 2 more bottles of beer on the wall, 2 more bottles of beer! So take one down, pass it around, 1 more bottle of beer on the wall! 1 bottle of beer on the wall, 1 bottle of beer! So take it down, pass it around, no more bottles of beer on the wall! Example 15: ```python # Nested Loops # Python programming language allows to use one loop inside another loop. # Syntax: # for iterator_var in sequence: # for iterator_var in sequence: # statements(s) # statements(s) # Example:- for i in range(1, 5): for j in range(i): print(i, end=' ') print() ``` 1 2 2 3 3 3 4 4 4 4 Example 16: ```python l = [ 'hello','hi',1,2,3,4,3.6j,['hi','bye','bye bye'],123,23,3,2] for var in l : print(var) ``` hello hi 1 2 3 4 3.6j \['hi', 'bye', 'bye bye'] 123 23 3 2 Example 17: ```python for var in range(1,20,2): if var % 2 == 0 : break elif var % 3 == 0 : continue print("Hello World") else : print("Good to Go ") ``` Output Hello World Hello World Hello World Hello World Hello World Hello World Hello World Good to Go Example 18: ```python l = [ 1,2,3,4,5,6,7,8,9,10 ] n = int(input("Enter a number : ")) for var in l : print(var*n) ``` Output Enter a number : 5 5 10 15 20 25 30 35 40 45 50 Example 19: ```python for letter in 'Python': print('Current Letter :', letter) fruits = ['banana', 'apple', 'mango'] for fruit in fruits: print('Current fruit :', fruit) print("Good bye!") ``` Output Current Letter : P Current Letter : y Current Letter : t Current Letter : h Current Letter : o Current Letter : n Current fruit : banana Current fruit : apple Current fruit : mango Good bye! Example 20: ```python # Iterating by Sequence Index fruits = ['banana', 'apple', 'mango'] for index in range(len(fruits)): print('Current fruit :', fruits[index]) print("Good bye!") ``` Current fruit : banana Current fruit : apple Current fruit : mango Good bye! Dictionary doesn't remember order (sequence), that's why we use another data type in python orderedDict Example 21: ```python d = { 'name' : 'python', 'version': 3.6, 'father' : 'Guido Van Rossum', 'named on ' : 'Monty Python', 'method' : 'OOPS', 'type' :'interpreted', 'year' : 1991, } for var in d: print(var,'=',d[var]) s = { 'hello', 'hi',1,2,3,4,5,6,'good to go','bye bye' } for var in s : print(var) ``` Output name = python version = 3.6 father = Guido Van Rossum named on = Monty Python method = OOPS type = interpreted year = 1991 1 2 3 hello 4 5 6 hi bye bye good to go Example 22: ```python l = [ (1,2,3),('hello','hi','how are you'),('good','bye','bye',),('hello','world','!!',),('python','java','c'),'c++',['oh','my','god' ] ] c = 1 for val1,val2,val3 in l : print("Iteration ",c) print("Value 1 = ",val1) print("Value 2 = ",val2) print("Value 3 = ",val3) c = c + 1 print("\n") ``` Output Iteration 1 Value 1 = 1 Value 2 = 2 Value 3 = 3 Iteration 2 Value 1 = hello Value 2 = hi Value 3 = how are you Iteration 3 Value 1 = good Value 2 = bye Value 3 = bye Iteration 4 Value 1 = hello Value 2 = world Value 3 = !! Iteration 5 Value 1 = python Value 2 = java Value 3 = c Iteration 6 Value 1 = c Value 2 = + Value 3 = + Iteration 7 Value 1 = oh Value 2 = my Value 3 = god Example 23: ```python l1 = [ 1,34,56,34,2,364,57,42,13,4,65,63,3,12,2,3456,] l2 = [ 1,3,4,42,67,346,57,5434,2,34,657,434,2,346,34,34] for val1,val2 in zip(l1,l2) : print("val1 = ",val1) print("val2 = ",val2) print() ``` Output val1 = 1 val2 = 1 val1 = 34 val2 = 3 val1 = 56 val2 = 4 val1 = 34 val2 = 42 val1 = 2 val2 = 67 val1 = 364 val2 = 346 val1 = 57 val2 = 57 val1 = 42 val2 = 5434 val1 = 13 val2 = 2 val1 = 4 val2 = 34 val1 = 65 val2 = 657 val1 = 63 val2 = 434 val1 = 3 val2 = 2 val1 = 12 val2 = 346 val1 = 2 val2 = 34 val1 = 3456 val2 = 34 Example 24: ```python for var in range(1,20) : print(var,end=",") ``` Output 1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19, Example 25: ```python for var in range(1000,0,-1) : if var % 2 == 0 and var % 3 == 0 and var % 5 == 0 : print(var,end=', ') ``` Output 990, 960, 930, 900, 870, 840, 810, 780, 750, 720, 690, 660, 630, 600, 570, 540, 510, 480, 450, 420, 390, 360, 330, 300, 270, 240, 210, 180, 150, 120, 90, 60, 30, Example 26: ```python l = [ 10, 34, 2, 56, 23, 567, 34, 232, 12, 345, 76, 44, 213, 45, 12, 456 ] for var in range(len(l)-1): for var2 in range(var+1,len(l)) : if l[var] >= l[var2] : l[var],l[var2]=l[var2],l[var] print(l) ``` Output: \[2, 10, 12, 12, 23, 34, 34, 44, 45, 56, 76, 213, 232, 345, 456, 567]