Python is a general-purpose, high-level programming language designed to be easy to read and execute. It is open-source, which means it is free to use. In this article, we will learn one of Python programming's fundamental looping statements: the Python for loop.
What Is for Loop in Python?
The for loop in Python is used to iterate over a sequence, which could be a list, tuple, array, or string.
Syntax: FOR COUNTER IN SEQUENCE:
STATEMENT(S)
Block Diagram:
Fig: Flowchart of for loop
Example:
Fig: Basic example of Python for loop
The program operates as follows: We have assigned a variable, x, which is going to be a placeholder for every item in our iterable object. In this case, the variable “x” actually represents the elements in that list. Then, we print our variable, x. This process continues until all items are printed.
Break Statement in for Loop
The Python break statement is used to exit from the loop immediately after a certain condition is met.
Example:
Fig: break statement
The program above operates as follows: The loop continues until the specified element is encountered. As soon as the ‘green’ element is encountered, the loop breaks.
Continue Statement in for Loop
The function of the continue statement is to skip the current iteration of a loop and continue with the next one.
Example:
Fig: continue statement
The Range() Function
The range() function executes a group of statements for a specified number of times.
Example:
Fig: range() function in Python for loop
The program operates as follows. When the for structure begins executing, the function
range creates a sequence of values, which range from zero to four. The first value in this sequence is assigned to the variable x, and the body of the for structure executes. For each subsequent value in the sequence, the value is assigned to variable x, and the body of the for structure executes. This process continues until all values in the sequence have been processed.
Else in for Loop
Python enables an else clause at the end of a for loop. The else part is executed if the loop terminates naturally.
Example:
Fig: else statement
In the above example, the for loop is executed first. After that, the else part is executed.
Nested Loops
A loop inside another loop is called a nested loop. The inner loop will be performed once for each iteration of the outer loop.
Example:
Fig: Nested loop in Python for loop
Recommended programming practice:
Excessive nesting levels can make it difficult to follow the program. As a general rule, try to avoid using more than three levels of indentation.
Access Index in for Loop
To iterate over the indices in a sequence, we use the enumerate() function.
Example:
Fig: enumerate() function
The enumerate() function adds the counter to iterable, which starts from zero by default.
Looping Through Multiple Lists
We can loop through multiple lists at once. For this, we use the zip() function, which is built in the Python loop.
Example:
Fig: Looping through multiple lists
For loop Exercise
Question 1: Display a “simplilearn” message after successfully executing for loop
Solution:
Fig: Question 1 solution
Question 2: You are given a list of integer elements. Make a new list that will store squares of elements from the previous list.
Solution:
Fig: Question 2 solution
Iterating by Using Index of Sequence Code Output
In python, one can iterate with the help of an index of sequential code in For Loop such as string with a For Loop, list with a For Loop, and tuple with a For Loop.
How to Iterate Over a String With a For Loop
A string with a For Loop can be iterated with the help of single, double or triple quotes for characters or numbers. Eg 'Hello World!' in single quotes, "hello" in double quotes or '''hello''' in triple quotes.
Example:
In [1] #indexing
H="Hello"
print(H[0])
#negative indexing
print(H[-4])
String Output:
H
e
How to Iterate Over a List With a For Loop
Square bracket is used for a python list with a For Loop. Besides, There are various types of inbuilt functions in the list that we can apply for particular tasks.
Such as
- clear() function to remove the elements from the list
- copy() function to return a copy of elements from the list
- insert() function to add a specific element to a specific position
- append() function to add elements in the end of the list
- pop() function to remove element from a particular position
- remove() function to remove the elements with particular value from the list
- reverse() function to make the order of the list reverse
- count() function to return the number of elements with specified value
- index() function to return an index of the elements in the list
Example:
num=[4, 5, 6, 7]
print(num)
letter=['p', 'q', 'r', 's']
print(letter)
List Output:
[4, 5, 6, 7]
['p', 'q', 'r', 's']
How to Iterate Over a Tuple With a For Loop
Tuple is used to hold data types by enclosing parentheses "()" and commas to separate every different element. Also, for index as an integer value, we write parenthesis in square bracket form ([1]).
Example
City= ("Nagpur", "Pune", "Nashik", "Mumbai", "Delhi", "Goa")
print (city[2])
Tuple Output:
Nashik
How to Iterate Over a Set With For Loop
Usually items in a Set are kept in random form, they don't have a specific index. However, with the help of 'in' keyword and for loop in python, we can loop the items in set with specified value.
Example:
thisset = {"wheat", "bajra", "pulses", "rice"}
for x in thisset:
print(x)
Set Output:
wheat
bajra
pulses
rice
How to Iterate Over a Dictionary With For Loop
A Dictionary with a For Loop in Python can be used to return a value with specified rules.
Example:
In the below example, the dictionary function can return a value as well as a key concerning a particular item.
thisdict = {
"brand": "Ford",
"model": "Mustang",
"year": 1964
}
for x, y in thisdict.items():
print(x, y)
Dictionary Output:
brand Ford
model Mustang
year 1964
for loop With else Output
Else in for loop can be executed if the for loop terminates naturally first and later else output can be executed.
Example:
In [1] : colours = ['purple', 'blue', 'white', 'golden']
For x in colours:
print(x)
else:
printf("finished!")
Else Output:
purple
blue
white
golden
finished!
While Loop
While loop in python is used to execute statements when the condition satisfies the true value. While loop requires to define a specific relevant variable such as indexing variable 'i' = 1.
Example:
i= 1,
while i<7 :
print(i)
i+=1
While Output:
1
2
3
4
5
6
Single Statement While Block Note
This is similar to if statement when a while Statement has only a single statement. Thus it can be put with a header line.
Example:
flag = 1
while (flag): print 'This is my home!'
print "Good bye!
Output:
This is my home!
for in Loop Syntax Output
Syntax:
For counter in sequence:
Statement (S)
Loop Control Statements
There are 3 different types of Loop control Statements in python, they are continue, break and pass concerning requirements of the loop.
Continue Statement
Continue Statement in Python is used to iterate the next element in the loop by skipping the current iteration.
Example:
In [1] : colours = ['purple', 'blue', 'white', 'golden']
For x in colours:
print(x)
if x=="white":
continue
Continue Output:
purple
blue
white
golden
Break Statement
Break Statement in Python is used to exit from a loop under certain conditions. In the below example, the statement breaks at 'white' and only executes the elements before 'white' .
Example:
In [1] : colours = ['purple', 'blue', 'white', 'golden']
For x in colours:
print(x)
if x=="white":
break
Break Output:
purple
blue
white
Pass Statement
Pass Statement in Python is used when the user doesn't know which particular code should be written. This is also called a null statement. We usually write comments in the code, though it is ignored by the interpreter and there is no effect on code. However, with pass Statement can be used in conditional statement format to define the various elements.
Example:
a=20
b=40
if (a<b):
pass
else:
printf("b<a")
How Does the "for" loop in Python Work Internally?
Internal for loop in python or one loop into another loop in python also called as nested loop. The iteration of the inner loop in python can be executed every once with respect to every outer loop iteration.
Example:
In [1] : colours = ['purple', 'blue', 'white']
fruits= ['mango', "banana", '''apple''']
for x in colours:
for y in fruits:
print(x,y)
Inner For loop (nested loop)
Output:
purple mango
purple banana
purple apple
blue mango
blue banana
blue apple
white mango
white banana
white apple
Conclusion
In this article, we have discussed Python for loop and its syntax different statements. We also provided a visual example that demonstrated how to use the break and continue statements in a Python for loop.
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