The for keyword in Python is a powerful tool for iterating over sequences, such as lists, tuples, strings, and dictionaries. It enables you to execute a block of code repeatedly for each item in the sequence. This eliminates the need for manual index tracking, making your code concise and readable. Let's explore how to use for loops effectively.
Basic Loop Structure
The fundamental structure of a for loop is:
for item in sequence:
# Code to be executed for each item
Here's how it works:
item: This variable represents the current element from the sequence during each iteration.sequence: This can be any iterable object, such as a list, tuple, string, or dictionary.
Looping Through Lists
Let's start with a simple example of iterating through a list of fruits:
Example 1: Looping Through a List of Fruits
fruits = ["apple", "banana", "cherry"]
for fruit in fruits:
print(fruit)
Output:
apple
banana
cherry
In this example, the for loop iterates over each element in the fruits list. For each fruit, the code inside the loop prints its name.
Looping Through Strings
Strings are also iterable sequences, allowing you to process each character individually:
Example 2: Looping Through Characters in a String
name = "Python"
for letter in name:
print(letter)
Output:
P
y
t
h
o
n
The loop iterates over each character in the name string, printing each one.
Looping Through Dictionaries
Dictionaries, with their key-value pairs, require a slightly different approach. We can iterate through the keys, values, or both:
Example 3: Iterating Through Dictionary Keys
person = {"name": "Alice", "age": 30, "city": "New York"}
for key in person:
print(key)
Output:
name
age
city
Example 4: Iterating Through Dictionary Values
person = {"name": "Alice", "age": 30, "city": "New York"}
for value in person.values():
print(value)
Output:
Alice
30
New York
Example 5: Iterating Through Dictionary Key-Value Pairs
person = {"name": "Alice", "age": 30, "city": "New York"}
for key, value in person.items():
print(f"Key: {key}, Value: {value}")
Output:
Key: name, Value: Alice
Key: age, Value: 30
Key: city, Value: New York
Range Function for Number Sequences
The range() function is incredibly useful for generating sequences of numbers. It's often used in conjunction with for loops:
Example 6: Iterating Over a Range of Numbers
for i in range(5):
print(i)
Output:
0
1
2
3
4
This loop iterates from 0 up to (but not including) 5.
You can also specify a starting number and step value:
for i in range(2, 10, 2):
print(i)
Output:
2
4
6
8
Nested Loops
For complex tasks, you can nest for loops within each other:
Example 7: Nested Loop for Multiplication Table
for i in range(1, 6):
for j in range(1, 6):
print(f"{i} x {j} = {i * j}")
print("----")
Output:
1 x 1 = 1
1 x 2 = 2
1 x 3 = 3
1 x 4 = 4
1 x 5 = 5
----
2 x 1 = 2
2 x 2 = 4
2 x 3 = 6
2 x 4 = 8
2 x 5 = 10
----
3 x 1 = 3
3 x 2 = 6
3 x 3 = 9
3 x 4 = 12
3 x 5 = 15
----
4 x 1 = 4
4 x 2 = 8
4 x 3 = 12
4 x 4 = 16
4 x 5 = 20
----
5 x 1 = 5
5 x 2 = 10
5 x 3 = 15
5 x 4 = 20
5 x 5 = 25
----
Break and Continue Statements
break: Exits the innermost loop prematurely.continue: Skips the remaining code in the current iteration and moves to the next one.
Example 8: Using 'break' to Exit Early
for i in range(10):
if i == 5:
break
print(i)
Output:
0
1
2
3
4
Example 9: Using 'continue' to Skip Iterations
for i in range(10):
if i % 2 == 0:
continue
print(i)
Output:
1
3
5
7
9
for Loop: A Versatile Tool
The for loop in Python is a versatile tool for automating repetitive tasks and working with sequences. Mastering its usage is crucial for efficient and elegant Python programming.
