Python for loop

T he for loop in Python has the ability to iterate over the items of any sequence, such as a list or a string . Syntax: T he syntax of a for loop look is as follows: for iterating_var in sequence: statements(s) If a sequence contains an expression list, it is evaluated first. T hen, the first item in the sequence is assig ned to the iterating variable iterating_var. Next, the statements block is executed. Each item in the list is assig ned to iterating_var, and the statement(s) block is executed until the entire sequence is exhausted. Flow Diag ram: Example: #!/usr/bin/python for letter in 'Python': # First Example print 'Current Letter :', letter fruits = ['banana', 'apple', 'mango'] for fruit in fruits: # Second Example print 'Current fruit :', fruit print "Good bye!" When the above code is executed, it produces the following result: Current Current Current Current Current Letter Letter Letter Letter Letter : : : : : P y t h o Current Letter : n Current fruit : banana Current fruit : apple Current fruit : mango Good bye! Iterating by Sequence Index: An alternative way of iterating throug h each item is by index offset into the sequence itself. Following is a simple example: #!/usr/bin/python fruits = ['banana', 'apple', 'mango'] for index in range(len(fruits)): print 'Current fruit :', fruits[index] print "Good bye!" When the above code is executed, it produces the following result: Current fruit : banana Current fruit : apple Current fruit : mango Good bye! Here, we took the assistance of the len() built-in function, which provides the total number of elements in the tuple as well as the rang e() built-in function to g ive us the actual sequence to iterate over. The else Statement Used with Loops Python supports to have an else statement associated with a loop statement. If the else statement is used with a for loop, the else statement is executed when the loop has exhausted iterating the list. If the else statement is used with a while loop, the else statement is executed when the condition becomes false. T he following example illustrates the combination of an else statement with a for statement that searches for prime numbers from 10 throug h 20. #!/usr/bin/python for num in range(10,20): #to iterate between 10 to 20 for i in range(2,num): #to iterate on the factors of the number if num%i == 0: #to determine the first factor j=num/i #to calculate the second factor print '%d equals %d * %d' % (num,i,j) break #to move to the next number, the #first FOR else: # else part of the loop print num, 'is a prime number' When the above code is executed, it produces the following result: 10 11 12 13 14 15 16 17 18 19 equals 2 * is a prime equals 2 * is a prime equals 2 * equals 3 * equals 2 * is a prime equals 2 * is a prime 5 number 6 number 7 5 8 number 9 number