Definite Iteration
Definite iteration is a programming concept that allows us to execute a set of instructions repeatedly. A program that utilizes definite iteration relies on loops to repeat a certain block of code until a condition is met.
Definite iteration is a fundamental part of programming, and it is essential to any developer’s repertoire. In this article, we will explore the various types of definite iteration that exist in programming, such as the numeric range loop, the three-expression loop, and the Python for loop.
We will also discuss how to iterate through a dictionary.
Numeric Range Loop
One of the most common types of definite iteration is the numeric range loop.
This type of loop iterates through a range of numbers specified by the programmer. Numeric range loops are used when you know in advance exactly how many times you want to execute a certain block of code.
The syntax for a numeric range loop varies depending on the programming language being used. In many programming languages, you would use a for loop to iterate through a numeric range.
Three-Expression Loop
The three-expression loop is another type of definite iteration. In this type of loop, the programmer sets up three expressions: the initialization expression, the ending condition expression, and the action expression.
The initialization expression is executed only once at the beginning of the loop. The ending condition expression is then evaluated, and if it is true, the action expression is executed.
After the action expression is executed, the ending condition is evaluated again. This process continues until the ending condition expression evaluates to false.
Three-expression loops are usually used when the programmer needs more control over the loop’s execution.
The Python for Loop
The for loop in Python is one of the most commonly used types of definite iteration.
Python’s for loop differs from a traditional for loop in that it is not limited to iterating over a numeric range. Instead, the Python for loop can iterate over any iterable object.
An iterable object is an object that can return an iterator. The iterator is then used to traverse the iterable object one item at a time.
Examples of iterable objects include lists, tuples, and dictionaries.
Iterators
In Python, an iterator is an object that enables you to traverse a sequence of data.
The iterator is created by calling the iter() function on an iterable object. When we call the iter() function on an iterable object, the iterator’s __iter__() method is called, and it returns the iterator object.
The iterator then has a __next__() method that returns the next value in the sequence. When there are no more values to return, the __next__() method raises the StopIteration exception.
Iterables
Iterables are objects that can be iterated upon. In Python, an iterable is an object that implements the __iter__() method.
When the __iter__() method is called, it returns an iterator object that can traverse the iterable object. Examples of iterables include lists, tuples, and dictionaries.
The Guts of the Python for Loop
The Python for loop is a high-level construct that is built on top of the __iter__() and __next__() methods of iterators. When we use a for loop in Python, the interpreter first calls the iter() function on the iterable object.
This returns an iterator object that can traverse the iterable object. The interpreter then calls the __next__() method on the iterator object to get the next value in the sequence.
This process continues until the iterator raises the StopIteration exception. The for loop then exits gracefully.
Iterating Through a Dictionary
Iterating through a dictionary is slightly different from iterating through other iterable objects. Dictionaries are built on key-value pairs, and we often need to access both the keys and values of a dictionary during iteration.
In Python, we can use the items() method of a dictionary to get a list of key-value pairs. We can then iterate over this list using a for loop.
In conclusion, definite iteration is a fundamental concept in programming, and it is essential to any developer’s repertoire. We have discussed the various types of definite iteration that exist in programming, such as the numeric range loop and the three-expression loop.
Additionally, we discussed the Python for loop, iterators, and iterables. We have also explored how to iterate through a dictionary.
By understanding definite iteration, you will be able to write more efficient and effective programs.
The range() function
The range() function is a built-in Python function that returns an iterable sequence of integers.
It is widely used in Python programs, especially with for loops. The range() function can be used with one or more arguments, depending on the desired sequence of integers.
In this article, we will discuss how to use the range() function with different arguments, and how it can be used in loops.
Syntax
The syntax of the range() function is as follows:
range([start], stop[, step])
The range() function takes at least one argument, stop, which specifies the end of the sequence.
If start is not provided, it defaults to 0. If step is not provided, it defaults to 1.
The range() function can be used in many different ways.
range()
When one argument is passed to the range() function, it creates an iterable sequence of integers from 0 up to (but not including) that argument.
This sequence is most commonly used to control the number of times a loop iterates. For example, the following code prints the numbers from 0 to 9:
for i in range(10):
print(i)
Output:
0
1
2
3
4
5
6
7
8
9
range(, , )
The range() function can also take three arguments to create a sequence of integers starting from a specific point, with a specified stride. The first argument is the starting point (inclusive), the second argument is the endpoint (exclusive), and the third argument is the stride.
For example, the following code prints the even numbers from 0 to 10:
for i in range(0, 11, 2):
print(i)
Output:
0
2
4
6
8
10
The range() function can be used in more complex loops that require iteration over a specific sequence of integers. In addition, iterating over a range object may be more efficient than creating a list object when you don’t need to store the sequence in memory.
Iterating over range objects
Once a range object is created, it can be iterated over using a for loop. The loop will iterate over each integer in the range, up to the specified end point.
For example, the following code prints the integers from 5 (inclusive) to 10 (exclusive):
for i in range(5, 10):
print(i)
Output:
5
6
7
8
9
The for loop can also be used with the range() function to iterate over a range object with a specified stride. The following code prints the integers from 0 to 10 in steps of 2:
for i in range(0, 11, 2):
print(i)
Output:
0
2
4
6
8
10
Conclusion
In summary, the range() function is a powerful built-in function in Python that returns an iterable sequence of integers. It can be used to control the number of iterations in a loop and iterate over a specific sequence of integers.
The range() function takes one or more arguments, depending on the desired sequence. By understanding how to use the range() function, you can write more efficient and effective Python programs.
Definite iteration in programming is an essential concept every programmer should master. The range() function in Python is a widely used construct for definite iteration, allowing the creation of an iterable sequence of integers.
By understanding the different arguments of the range() function, programmers can create efficient for loops that iterate over specific sequences of integers. The range() function also provides a simple way to iterate over a sequence of integers that doesn’t require memory storage.
By mastering definite iteration, programmers can write more efficient and effective programs that take advantage of Python’s built-in functions.