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5.4 FOR LOOPS
Similarly to the while loop, a for loop is used for repeating a block of code multiple times, thus making it easier to work with data sequences, such as lists, strings, or ranges of numbers.
A for loop in Python iterates over a sequence, such as a list or a string. This means you can execute a code block for each item in the sequence, one after the other. for loops are handy for tasks that require you to act on each item in a sequence, like adding or modifying elements, checking conditions, or performing calculations.
The basic structure of a for loop looks like the following.
for i in sequence:
# Do something with item
i is a variable that takes the value of the next item in the sequence on each iteration. You can name it anything you want, but usually, it should be descriptive of the data you're working with to make the code more readable. sequence is the sequence you want to iterate over, like a string.
This flowchart demonstrates how a for loop works. As we mentioned, for loops are used to iterate over objects. Taking the example of a string, you can think of it as sequentially working its way through every character in the string and asking itself on each iteration whether it has ran out of characters to work through. Until it hasn't reached the end, the body of the loop will be executed. Once it reaches the end of the string, the loop exits and the program continues execution from the statement immediately after.
Flowchart. For-loop flowchart. geeksforgeeks.org
Here's a simple example that prints each letter in a string.
name = "Peeter"
for letter in name:
print(letter)
'''
This loop will print out all the characters, each of them on a new line.
P
e
e
t
e
r
'''
USING THE RANGE FUNCTION
The range() function is often used with for loops to generate a sequence of numbers, which you can then iterate over:
for i in range(5):
print(i)
This will print numbers 0 through 4. range(5) generates a sequence of numbers from 0 to 4, and the for loop iterates over each number.
for loops should be preferred when the number of iterations is known.
KEY THINGS TO REMEMBER
forloops are used to iterate over a sequence.- The loop starts with the
forkeyword, followed by a variable name representing the current item, then theinkeyword, and the sequence to iterate over. - Each iteration assigns the next item in the sequence to the variable and executes the code block within the loop.
- The
range()function is used to generate a sequence of numbers, which the for loop can then iterate over to act a desired number of times. - The variable used in the
forloop can be named anything, but it should be descriptive to make the code easily understandable.
SELF-CONTROL EXERCISES
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