Python for Loop

Hello Learners… In this session, you’ll learn to iterate over a sequence of elements using the different variations of for loop.

Python For Loops

A for loop is used for iterating over a sequence (that is either a list, a tuple, a dictionary, a set, or a string).

This is less like the for keyword in other programming languages, and works more like an iterator method as found in other object-orientated programming languages.

With the for loop we can execute a set of statements, once for each item in a list, tuple, set etc.

Example: Print each fruit in a fruit list:

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fruits = ["apple", "banana", "cherry"] for x in fruits:   print(x)

The for loop does not require an indexing variable to set beforehand.

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Looping through a String

Even strings are iterable objects, they contain a sequence of characters

Loop through the letters in the word “Arjun Pinpoint”:

1 2	for x in "Arjun Pinpoint":   print(x)

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The break Statement

With the break statement we can stop the loop before it has looped through all the items

Exit the loop when x is “banana”:

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fruits = ["apple", "banana", "cherry"] for x in fruits:   print(x)   if x == "banana":     break

Exit the loop when x is “banana”, but this time the break comes before the print:

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fruits = ["apple", "banana", "cherry"] for x in fruits:   if x == "banana":     break   print(x)

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The continue Statement

With the continue statement we can stop the current iteration of the loop, and continue with the next

Do not print banana:

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fruits = ["apple", "banana", "cherry"] for x in fruits:   if x == "banana":     continue   print(x)

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The range( ) function

To loop through a set of code a specified number of times, we can use the range() function,

The range() function returns a sequence of numbers, starting from 0 by default, and increments by 1 (by default), and ends at a specified number.

Using the range() function:

1 2	for x in range(6):     print(x)

Note that range(6) is not the values of 0 to 6, but the values 0 to 5.

The range() function defaults to 0 as a starting value, however it is possible to specify the starting value by adding a parameter: range(2, 6), which means values from 2 to 6 (but not including 6)

Using the start parameter:

1 2	for x in range(2,6):     print(x)

The range() function defaults to increment the sequence by 1, however it is possible to specify the increment value by adding a third parameter: range(2, 30, 3)

Increment the sequence with 3 (default is 1):

1 2	for x in range(2,30, 3):     print(x)

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Else in For Loop

The else keyword in a for loop specifies a block of code to be executed when the loop is finished

Print all numbers from 0 to 5, and print a message when the loop has ended:

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for x in range(6):     print(x) else:     print("Finally finished!")

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Nested Loops

A nested loop is a loop inside a loop.

The “inner loop” will be executed one time for each iteration of the “outer loop”

Print each adjective for every fruit:

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adj = ["red", "big", "tasty"] fruits = ["apple", "banana", "cherry"]   for x in adj:     for y in fruits:         print(x, y)