Python For Loop

The for Loop in Python

The for loop is used to execute a block of code multiple times by iterating over a sequence (such as a list, tuple, string, or range of numbers). It is essential for automating repetitive tasks and simplifying code.

Syntax of the for Loop

The general structure of a for loop in Python is as follows:

for variable in sequence:
    code_block

• variable: successively takes each value from sequence.
• sequence: a collection of elements to iterate over (list, tuple, string, etc.).
• code_block: instructions executed in each iteration.

Example with a List

Let's iterate over a list of numbers and print each element:

numbers = [1, 2, 3, 4, 5]
for number in numbers:
    print(number)

Output:

1
2
3
4
5

Using the range() Function

The range() function generates a sequence of numbers, often used with for:

for i in range(5):
    print(i)

Output:

0
1
2
3
4

range(5) generates numbers from 0 to 4 (5 excluded).

Specifying a Start and Step

for i in range(1, 10, 2):
    print(i)

Output:

1
3
5
7
9

• 1: start value
• 10: stop value (not included)
• 2: step between values

Iterating Over a String

word = "Python"
for letter in word:
    print(letter)

Output:

P
y
t
h
o
n

Each character is treated as an element of the sequence.

Using enumerate()

enumerate() allows retrieving both the index and the value:

fruits = ["apple", "banana", "cherry"]
for index, fruit in enumerate(fruits):
    print(f"{index} : {fruit}")

Output:

0 : apple
1 : banana
2 : cherry

Using zip()

zip() allows iterating over multiple lists simultaneously:

names = ["Alice", "Bob", "Charlie"]
ages = [25, 30, 35]
for name, age in zip(names, ages):
    print(f"{name} is {age} years old.")

Output:

Alice is 25 years old.
Bob is 30 years old.
Charlie is 35 years old.

The else Clause in for

A for loop can have an else clause executed after the loop if no interruption (break) occurs:

for i in range(3):
    print(i)
else:
    print("Loop completed")

Output:

0
1
2
Loop completed

If a break interrupts the loop, else does not execute.

Conclusion

• for allows iterating over sequences such as lists, tuples, and strings.
• range() is useful for generating number sequences.
• enumerate() and zip() facilitate handling indices and multiple lists.
• The else clause executes if the loop is not interrupted.

Using for effectively makes code more concise and readable.