Distinctive Analytics

For loop is one of the most useful methods to reuse code for repetitive execution. This loop is very common in computer languages, but when it comes to Python, there are significant improvements in the for loop more than in other languages. For loops run a code in a loop until given conditions are met.

The basic structure of for loop

In the following code implementation, you can see the basic structure of the for loop. We are iterating through the list “num” from 1 to 10.

num=[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
for i in num:
    print(i)

1
2
3
4
5
6
7
8
9
10

If you compare this loop with c++/c/ java languages, you will see one difference that makes these codes more complex and lengthy.

Java implementation of for loop

import java.io.*;
class forward_loop{
    public static void main(String args[])
    {
        int list[]={1,2,3,4,5,6,7,8,9,10};
        int count=0;
        for (int i=0;i<10; i++){
            count=count+1;
            System.out.println(list[i]+" ");
        }
    }
}

C++ Implementation of for-loop

using namespace std;
int main()
    {
        int list[5]={1,2,3,4,5,6,7,8,9,10}
        for (int i=0;i<10;i++)
        {
            cout << list[i] << "\n";
        }
        return 0;
    }

Observe the difference between these codes and Python code. Python code has only 3 lines and is fairly understandable. Java and C++ codes span over 10 lines and may look ambiguous to a newcomer.

Range Function

The range is an independent function, but it is popularly used for loops. It creates an iterable number generator with given parameters.

Range function has 3 arguments ”range (start, stop, step)”. It can operate with 1 stop argument. By giving a stop argument, the range will iterate over 0 to stop.

range(0,10,2)

The range can operate with a minimum of 1 argument. Remember that range does not return a list. It returns numbers per cycle.

list(range(0,10,2))

[0,2,4,6,8]

num=[1,2,3,4,5]
for i in range( 5 ):
    print(num[i])

1
2
3
4
5

It can operate with 2 arguments (start, stop). By giving these arguments, the range will iterate from start to stop.

for i in range(1,5):
    print(i)

1
2
3
4

It can operate with 3 arguments (start, stop, step). By giving these arguments, the range will iterate from start to stop and with skip numbers with each step.

for i in ranage(0,10,2):
    print(i)

0
2
4
6
8

List comprehension with For

Let’s vary the look of the output with simple in changes in print. Using the end parameter cancels out the new line that executes with every print statement.

num=[x for x in range(5)]
for i in num:
    print(i,end=' ')

0 1 2 3 4

num=[x for x in range(5)]
for i in num:
    print(i,end='\t')

0    1    2    3    4

For loop with Strings

string='the quick browm fox jumps over the lazy dog'
for i in string:
    print(i,end='')

the quick browm fox jumps over the lazy dog

Continue Statement

We can use continue to end and start a new iteration in the for loop rather than executing the remaining body of code in the loop.

In the following example, we don’t want to print 4. So we skip if 4 occurs in x by using the continue statement.

even=[x for x in range(10) if x%2==0]
print(even)
for x in even:
    if x==4:
        continue
    print(x)

0
2
6
8
10
12
14
16
18

Pass Statements

We mostly use a pass statement in place of a code for the continuation of execution. If a scope of a function has no statement body, we can use pass in that scope to avoid any errors.

for i in even:
    pass

Observe in the following code there is no statement body of if, by using pass we are continuing to execute for loop.

for i in even:
    if i>0:
        pass
    print(i)

0
2
4
6
8

Nested For loops

Using a loop inside another loop, Scope creates a nested loop. By using nested loops, we can handle problems with complex and multiple recursive operating structures. It also gives the power to operate over matrix-like structures of lists that are Multi-Dimensional lists.

a = [[1,3,5,7],
     [2,4,6,8],
     [8,6,4,2],
     [7,5,3,1]]
for i in a:
    print(i)

[1, 3, 5, 7]
[2, 4, 6, 8]
[8, 6, 4, 2]
[7, 5, 3, 1]

Let’s perform a multiplication operation on a diagonal row in a matrix.

for i in range(len(a)):
    for j in range(len(a[i])):
        if i==j:
            a[i][j]*=20
        print(a[i][j],end=' ')
    print()

20 3 5 7
2 80 6 8
8 6 80 2
7 5 3 20

For loops with Else

The else block in a for-loop executes only if the loop has completed all of its iterations. If the iterations are interrupted in the for-loop, the else block won’t be executed.

no break

for i in range(1,4):
    print(i)
else:
    print("No Break")

1
2
3
No Break

with Break

for i in range(1,4):
    print(i)
    break
else: # Not executed as there is a break
    print("No Break")

1