Python has two types of loops :
- for loop
- while loop
The two loops are very specific in their use. for loops are often used for iterations over an object or a data structure . Like every character in a string or every object in a list. while loops are often used when the initial condition is known and a specific block of code is to be executed until that condition becomes false.
Let us understand Iteration Through For loop.
Let us take some examples based on for loops.
my_list = [1,2,3,4,5,6] for x in my_list: print(x) for x in my_list : print("hello world")
1 2 3 4 5 6 hello world hello world hello world hello world hello world hello world
Let us use for loop along with conditional statements . In the example below i have some numbers in my_list and i want to print only the even numbers.
my_list = [1,2,3,4,5,6] for num in my_list : # modulo operator would give the remainder of the division if num % 2 ==0: print(num)
2 4 6
Let us make use of a counter to calculate the sum of all the elements in a list. The counter should be assigned a value of zero initially and every element should be added to it every time a iteration is done. Let us see an example to understand this.
my_list = [1,2,3,4,5,6] my_sum = 0 for x in my_list : my_sum = my_sum + x print(my_sum)
Let us go ahead and iterate through a string and a tuple.
for x in "PY4U.org": print(x) my_tuple = ( 1,2,3 ) for x in my_tuple : print(x)
P Y 4 U . n e t 1 2 3
while loop executes a block of code while a condition is true . Syntax of the while loop is as follows:
- while Some_boolean_condition :
# block of code to be executed.
Let us take an example based on while loop. In the example below , we have to print all the numbers less than 7 using while loop. In such problems it is essential to use a counter such that when the value of counter becomes more than or equal to 7 , the loop should get terminated. Let us see the code below.
#always assign zero to your counter x = 0 while x < 7 : print(x) x = x+1
0 1 2 3 4 5 6
Sometimes it is required to use single or multiple loop(s) within a single parent loop. In the example given below , we have two lists and we want to store the product of each elements into a third list.
list_1 = [1,2,3,4] list_2 = [5,6,7] list_3 =  for x in list_1: for y in list_2: list_3.append(x*y) print(list_3)
[5, 6, 7, 10, 12, 14, 15, 18, 21, 20, 24, 28]