Python Coding Day 12 | Python Lists and Loops Explained
Python Lists and Loops Explained
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1. For Loop with Lists
The for loop is the most common way to iterate over the elements of a sequence, such as a list. It executes the code block once for each item in the list.
| Code | Explanation |
vehicles = ["Car", "Bike", "Bus"] | This line creates a list named vehicles containing three string elements. |
for vehicle in vehicles: | This is the start of the for loop. For each item in the vehicles list, it temporarily assigns that item to the variable vehicle. |
print(vehicle) | Inside the loop, this line prints the current element ("Car", then "Bike", then "Bus"). |
print("I like " + vehicle) | This line uses string concatenation to print a personalized sentence for the current vehicle. |
Practical Example:
This pattern is useful for processing every item in a dataset, like printing a report for every user in a list or applying a function to every file in a directory.
vehicles = ["Car", "Bike", "Bus"]
for vehicle in vehicles:
print(vehicle)
print("I like " + vehicle)
Output:
Car
I like Car
Bike
I like Bike
Bus
I like Bus
2. For Loop with Range
The built-in range() function generates a sequence of numbers, which is often used in for loops to control how many times the loop runs. It's especially useful when you need to repeat an action a specific number of times.
Example 1: range(stop) or range(start, stop)
| Code | Explanation |
for count in range(5, 20): | This loop uses range(start, stop). It generates numbers starting at 5 (inclusive) and goes up to but not including 20 (exclusive). The numbers generated are $5, 6, 7, \dots, 19$. |
print(count) | Prints the current number in the sequence. |
Practical Example (Counting Inventory):
for count in range(5, 20):
print(count)
Example 2: range(start, stop)
| Code | Explanation |
for value in range(50, 61): | This loop generates numbers starting at 50 (inclusive) and goes up to but not including 61 (exclusive). The numbers generated are $50, 51, \dots, 60$. |
print(value) | Prints the current number. |
Practical Example (A sequence of years):
for value in range(50, 61):
print(value)
Example 3: range(start, stop, step)
| Code | Explanation |
for step in range(2, 22, 4): | This loop uses the third argument to define a step (or increment). It starts at 2, goes up to (but not including) 22, and increases by 4 in each iteration. |
print(step) | Prints the current number in the sequence: $2, 6, 10, 14, 18$. |
Practical Example (Processing data every 4th entry):
for step in range(2, 22, 4):
print(step)
3. Calculating the total of numbers from 1 to 50
This is a classic example of using a for loop to perform an accumulation or running total.
| Code | Explanation |
sum_value = 0 | Initializes a variable to store the running total. It must start at 0 so the first number added is correct. |
for num in range(1, 51): | This loop iterates through the numbers from 1 up to 50 (since 51 is the exclusive stop value). The current number is stored in num. |
sum_value += num | This is a shorthand operator equivalent to sum_value = sum_value + num. In each loop, the current value of num (1, then 2, then 3, and so on) is added to the running total stored in sum_value. |
print("Total:", sum_value) | After the loop is complete (all numbers from 1 to 50 have been added), this line prints the final result. |
Practical Example:
This technique is fundamental for tasks like calculating the total cost of items in a shopping cart, aggregating sales data, or finding the sum of sensor readings.
sum_value = 0
for num in range(1, 51):
sum_value += num
print("Total:", sum_value)
Output:
Total: 1275
- by Chirana Nimnaka
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