Loops in Python

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Loops and Iterations

Loops are a fundamental concept in programming that allow for the repetition of a set of instructions until a certain condition is met. They help automate repetitive tasks, making the code more efficient, concise, and easier to maintain. For example, if you want to print a list of sustainable fashion brands, instead of writing each print statement separately, you can use a loop to iterate over a list containing those brands and print each one.

For Loop

The for loop is used to iterate over a sequence, such as a list, tuple, dictionary, set, or string. It is especially useful when you know the number of iterations in advance.

Syntax:

for variable in sequence:
    # Code block to be executed

Example: Iterating over a list of sustainable fashion brands.

brands = ["Patagonia", "Everlane", "Allbirds", "People Tree"]
for brand in brands:
    print(brand)

Output:

Patagonia
Everlane
Allbirds
People Tree

Iterating Over a List

You can use a for loop to iterate over each element in a list. This is useful when performing an operation on each item, such as applying a discount to a list of prices.

Example:

prices = [100, 200, 300, 400]
discounted_prices = []
for price in prices:
    discounted_prices.append(price * 0.9)  # Apply a 10% discount
print(discounted_prices)

Output:

[90.0, 180.0, 270.0, 360.0]

Iterating Over a String

A for loop can also iterate over the characters in a string, which is useful for tasks such as counting vowels or finding substrings.

Example:

text = "Sustainable Fashion"
for char in text:
    print(char)

Output:

S
u
s
t
a
i
n
a
b
l
e

F
a
s
h
i
o
n

Iterating with range()

The range() function is often used with a for loop to generate a sequence of numbers, especially when the number of iterations is known.

Example:

for i in range(1, 6):
    print(f"Collection {i}")

Output:

Collection 1
Collection 2
Collection 3
Collection 4
Collection 5

While Loop

The while loop repeats a block of code as long as a specified condition is true. It is useful when the number of iterations is not known beforehand.

Syntax:

while condition:
    # Code block to be executed

Example: Printing numbers from 1 to 5.

count = 1
while count <= 5:
    print(f"Design {count}")
    count += 1

Output:

Design 1
Design 2
Design 3
Design 4
Design 5

Control Statements: continue and break

The continue statement is used to skip the rest of the code inside a loop for the current iteration and move to the next iteration. The break statement is used to exit the loop prematurely.

Example with continue:

# Skip printing the brand "Allbirds"
brands = ["Patagonia", "Everlane", "Allbirds", "People Tree"]
for brand in brands:
    if brand == "Allbirds":
        continue
    print(brand)

Output:

Patagonia
Everlane
People Tree

Example with break:

# Stop printing when the brand is "Allbirds"
for brand in brands:
    if brand == "Allbirds":
        break
    print(brand)

Output:

Patagonia
Everlane

For more details, visit the official Python documentation on <a href="https://docs.python.org/3/tutorial/controlflow.html#for-statements">loops</a> and <a href="https://docs.python.org/3/tutorial/controlflow.html#break-and-continue-statements-and-else-clauses-on-loops">control flow statements</a>.

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The author of this entry is Gustavo Rodriguez. AI was used partially in the writing process.