Understanding Python Loops and Flow Control for Newbies

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Python is a high-level programming language for general-purpose scripting, as well as an interpreted and object-oriented programming language. This class will help you to learn the basics of Python by understanding loops and flow control.

“Python control flow exercises” is a newbie friendly article that explains the basics of Python loops and flow control. It also includes some code examples to help explain how each approach works.

Understanding Python Loops and Flow Control for Newbies

Python is one of the most extensively used programming languages in the world today. The loop concept is present in Python, as it is in practically all other programming languages. Python loops like the for and while loops enable programmers to cycle across collections or depending on criteria.

You’ll learn how to create and utilize each form of Python loop in this course, as well as how to control loops using the break, pass, and continue Python expressions.

Let’s get started!

Prerequisites

This article will be a step-by-step guide. Make sure you have Python 3.6 or later installed if you want to follow along. On a Windows 10 system, Python v3.9.2 will be used in this course.

How Do You Install Python 3.6? Related:How Do You Install Python 3.6?

Understanding Python Constructs That Can Be Iterated

You must first understand the idea of Python iterables before you can begin learning loops. Loops handle lists, tuples, and dictionaries, which are collections of items. You may “iterate over” numerous items in each of these structures. As a result, each construct is an iterable containing components that may be processed separately by a loop.

When you hear the term iterable, remember that it refers to a property that allows you to read each item in a collection using a loop.

Loops in Python

Let’s get this session going by learning about loops first. The execution of statements or blocks of statements controlled by an iterable expression is repeated in for loops. To put it another way, they run code for each item in a collection of items.

For Strings and Loops

For instance, suppose you had an iterable object like a string. A string in Python is a collection of characters. Each string is made up of a number of different characters. Perhaps you have the string ADAM. A, D, A, and M are the iterable characters in this string.

Python only recognizes one element as a single string: ADAM, as illustrated below.

Python has a single element.Python has a single element.

Python strings, on the other hand, are iterable, thus it can “split apart” a string into an array of characters and handle each character individually. To do so, use a for loop like the one below.

Each iteration of the for loop is represented by a target or iterator (in this example, a letter). The in keyword is then used to notify Python which iterable element (ATA) you want to process. The string contains every character in the character array.

Then, within the for loop, you may write any code you want for each iteration. Python is just outputting each character in the character array in this case (string).

ATA = “ADAM” in ATA for letter: print (letter)

Python prints each character in the string one by one, as seen below.

Using a for loop to print each character in a stringUsing a for loop to print each character in a string

Iterating over any iterable element, such as lists and ranges, is possible using for loops. Replace ATA with range(5) in the example in this section to get the same effect.

While Loops in Python

While for loops run code for each entry in a collection, the while loop runs code depending on a condition. Python, in particular, continues to run a while loop even if a condition is false.

In Python, for example, it’s typical to need to build a counter and run code a certain number of times. You’ll need to write a condition that returns True when the current count surpasses the maximum count to achieve this result.

Let’s imagine you have a variable named count that stores the number 0. You want to increase this number by one but not more than five. You might make something similar to this:

count = 0 count = count + 1 count = count + 1 count = count + 1 count = count + 1 count = count + 1 count = count + 1 count = count + 1 count = count + 1 print (count)

It’s possible that the above will work, but it’s not very efficient. The DRY concept isn’t being followed. You’re saying the same thing again and over. Rather, use a while loop and instruct Python to add one to count if count is less than six.

The below examples using a while loop to define a condition (count < 6) and to execute an expression (the print statement and increment the count by 1 while the condition is True.

count = 0 while (count < 6): print(‘The count is:’, count) count = count + 1

A Python while loop is shown.A Python while loop is shown.

Controlling Flow in Loops

Both the Python for and while loops began and terminated on their own in the preceding two instances. The while loop finished because its condition evaluated to True, and the for loop ended because it reached the end of the iterable collection.

Although it’s typical for Python loops to finish “naturally,” you may adjust the loop’s behavior to stop sooner or skip one or more iterations.

The Statement of Breakage

When you need to end a loop prematurely, you can do so by using The Statement of Breakage. When executed inside of a loop, The Statement of Breakage stops the loop at the current iteration.

Typically, you’ll use The Statement of Breakage when a specific condition is met inside of a loop. For example, in the previous for loop example, you learned a for loop will iterate over an array of characters in a string. Maybe you’d like to only process all characters up to the first D.

To end a for loop (or even a while loop), establish a condition to match on and then add a break expression, as illustrated below.

Python finishes the for loop in the example below when the iterator variable letter equals D.

ATA = “ADAM” in ATA for letter: print (letter) if letter == “D”: break

Demonstrating The Statement of Breakage in a Python loopDemonstrating The Statement of Breakage in a Python loop

Continue With This Statement

Perhaps you need to create a loop based on a specific condition but don’t necessarily want to process every iterable element. In that case, you can skip iterations with Continue With This Statement.

Unlike The Statement of Breakage that terminates the entire loop, Continue With This Statement skips the current iteration. Using the example from above, maybe you’d like to iterate over each character in the string ADAM but skip the D character. You could skip the D character using a condition (if letter == “D”) and Continue With This Statement, as shown below.

ATA = “ADAM” for letter in ATA: continue printing if letter == “D” (letter)

You can see below Python didn’t return the D character because Continue With This Statement skipped the print statement when it encountered the D character.

Using the continue command in PythonUsing the continue command in Python

The Statement of Passage

Let’s now finish off the flow control section with The Statement of Passage. The Statement of Passage is a bit unique in that it’s actually just a placeholder. The Statement of Passage is a way to define a loop in a Python script that actually does nothing.

Let’s imagine you have a for loop in your Python script that you’d want to keep for any reason. However, unlike the example below, you do not have an expression to run within it.

When you use an expression within a for loop in Python, Python will throw an IdentationError, as illustrated below.

Error due to the lack of a loop expressionError due to the lack of a loop expression

But, add The Statement of Passage as an expression inside of the for loop and you’ll see Python executes the for loop essentially doing nothing.

Using The Statement of PassageUsing The Statement of Passage

Conclusion

You learnt how to get started with Python loops in this article. Learning how Python loops function and how to manipulate them opens up a world of possibilities for writing and developing effective Python applications.

Where will you use your newfound understanding to create a loop in your code?

A “while loop in python” allows the programmer to repeat a block of code as long as a certain condition is met. The “while loop in python” can also be used for flow control, which is when you want your program to run a different set of instructions depending on what the user does.

Frequently Asked Questions

What do you understand by flow of control in Python?

A: The flow of control is defined as the order in which a program executes its statements. It can be said that Python has an explicit and implicit style for this. In explicit style, the flow of control begins with one statement, followed by another statement if its needed to continue execution from there. With implicit style, the flow usually starts at the first executable line of code after importing or starting a new file where all lines are executed strictly top-down without jumping back up when reaching end conditions like loops labeled break .

How do you control a loop in Python?

A: The full loop control must be broken into smaller pieces. You can use a while loop to wait for the current time to pass, then check if your desired action has been taken and execute it as needed.

What are the 3 loops in Python?

A:
1 – for i in xrange(10): print(Hello world)
2 – Boom = left_shift(boom) + b
3 – def f(): return 1

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