Python For Loop Statement

A loop statement often referred to as a loop, is a series of sequences repeated multiple times until a given condition or prerequisite is completed. It is a control flow statement for specifying iteration allowing a code to be repeatedly executed many times.

One of the basic structures of computer programming, a loop is a most basic and efficient and powerful programming concept. A loop asks the same questions repeatedly until an answer that requires no action is obtained. Iteration is the term used to refer to each time the question is asked.

A programmer who requires the same line of code multiple times can use a loop to save time.

For example, a program requires printing “HEY” 15 times. Instead of writing the same code repeatedly, the programmer can set up a loop to meet the above criteria. This also helps to combat being redundant.

Learn Software Development Courses online from the World’s top Universities. Earn Executive PG Programs, Advanced Certificate Programs or Masters Programs to fast-track your career.

For Loop: Definition

A loop statement is a series of steps or sequence of statements executed continuously zero or more times satisfying the given condition is satisfied.

Types of Loop in Python

Three types of a loop are used in the Python language. All these ways provide similar basic functionality but vary in syntax. The loops available in python programming languages are:

• While loop
• For loop
• Nested loop

WHILE LOOP

As long as the given requirement is true, the loop is executed. Until a given condition is satisfied, the block of statements is continuously executed. The line after the loop in the program is executed, as the condition becomes false.

Syntax: 

While condition:

 Statements(code)

There could be several conditions in a while loop. When the loop starts running out of conditions, it moves on to the next line of code.

FOR LOOP

The for loop in python is used to iterate over a sequence or other objects. Iteration over a sequence is known as traversal.

A python for loop enables the programmer to repeatedly execute a particular set of conditions until a previously specified condition is met.

For example, if you want to print numbers from 1 to 1000, writing individual codes for it would take forever. Here comes the implication of for loop.

The syntax for python for loop:

Val in sequence:

  Loop body

Val is the given value of the variable inside the sequence.

The loop is continued till we reach the last item in the sequence. The loop body is separated from other parts of the code using indentation.

Till we reach the last value of the variable, the loop is continued. Indentation is used to separate the body of the loop from the rest.

For loop using the range() function

A series or sequence of numbers can be generated using the range() function. If not specified otherwise, the starting value of the sequence defaults to 0. The increment of the sequence is by default 1, but it can also be changed.

The start, stop and step size is defined as 

range(start,stop,step_size)

The range function does not store values in its memory. The next number is generated on the go in accordance with the start, stop and step size.

If all the outputs must be forced out of the function, list() can be used.

To iterate through a sequence with indexing, the function len() can be used with the range() function in the python for a loop.

Else in for loop

If the keyword else is used in a python for loop indicates a code block to be executed when the loop is done. If a break statement stops the loop, the else block will not be implemented. Other languages like Java, C+, C++ do not allow the use of else statements with for loop.

NESTED LOOPS

Nested loops denote a loop inside another loop. Any type of loop can be used inside another. Loops like

• while loop inside for loop,
• for loop inside a while loop,
• while loop inside a while loop,
• for loop inside a for a loop.

The syntax for nested loops in python is:

While expression:

        While expression:

            Statement(s)

            Statement(s)

LOOP CONTROL STATEMENTS

Loop Control Statements are used to change the flow of a loop execution. Loop control statements are used if you want to skip an iteration or stop the progression. The execution of a loop can be changed from its normal sequence. 

Three types of loop control statements supported by python are:

• Break statement
• Continue statement
• Pass statement

Break Statement

Based on a given condition, this is used to bring the control out of the loop. The loop can be stopped before looping through all the items.

Continue Statement

A continue statement is used to stop the iteration of the current loop and to continue to the next. Unlike the break statement, the control is not brought out of the loop.

Pass Statement

A pass statement is used to write empty loops. Empty control statements, classes, and functions all use pass statements. If we want nothing to be done when the condition is met, a pass statement is used.

A passing statement is particularly useful when functionality is not required at present, but there is a need to implement it in the future. If you have a python for loop with no content, a pass statement is added so that an error does not occur.

How do loops in Python function?

Let us see the inner workings of a loop in python and how a function is executed. The steps can be broken down as follows:

• Creating a list of iterable objects with the iter() function.
• Till the Stopiteration is raised, run an infinite while loop.
• Fetch the next element in the try block with the next() function.
• The operation to be performed with the element is carried out after fetching the element.

Conclusion

While working with Python, loops are a powerful tool. Loops can be used for all kinds of interesting things while data analu=ysing with Python. Python for loops is usually used for iterable objects like a list, string, set, or tuple.

By defining the iterable object and then the function you want to perform, the function can be executed repeatedly till a specified criterion is met. 

Especially used in data analysis work, a python for loop tool is instrumental in saving time. Sorting through multiple rows and columns of data becomes a cakewalk once you get the hang of how loops work.

Other functions like range and break can also be implemented in the for loop, which furthers its uses.

We hope this article has provided you with an insight into the basics of python for loops. If you’d like to learn in-depth about control statements in Python, we recommend upGrad’s Advanced Certificate Program in Big Data from IIIT-Bangalore. The program is designed for working professionals aspiring to complete post-graduation without compromising on their job responsibilities. The 7.5-month course includes industry experts mentorship, a host of industry-relevant case studies and projects, and 360-degree career support.

In addition to a world-class curriculum and cutting-edge teaching solutions, students also get access to upGrad’s paid learner base of 40,000+, which opens numerous avenues for pursuing collaborative projects and progressing in your career.

Book your seat with us today!