Learning Python – Post 7: If-Else, For Loops, and Putting It All Together

Tonight was about bringing things together. I started exploring conditions (if, else, elif) and moved into loops — especially the for loop combined with range().

These two tools are powerful when you want to make decisions or repeat tasks. Here’s a breakdown of what I learned and some example code I worked through.

`if`, `elif`, `else` – Making Decisions

I started with the basics. Here’s how you can check if a number is positive or negative:

number = -4

if number > 0:
    print("The number is positive")
elif number < 0:
    print("The number is negative")
else:
    print("The number is zero")

Pretty straightforward, but one thing I had to get used to: indentation matters a lot in Python. If the print() lines aren’t indented correctly, the code won’t run or will give weird results. That’s something I caught myself doing wrong a couple times.

`for` Loops – Repeating Things

Next up: loops. I practiced going through lists and ranges using for.

Here’s a very basic loop:

nums = [2, 4, 6, 8]

for num in nums:
    print(num * num)

That prints the square of each number in the list.

Then I tried it with range() instead:

for i in range(1, 6):
    print(i * i)

Which prints:

You can also step through numbers with custom intervals:

for i in range(1, 21, 2):
    print(i * i * i)  # cubes of odd numbers from 1 to 20

Example: Analyzing Numbers from 1 to 20

Finally, I put everything together into one combined piece. It loops through numbers from 1 to 20, and for each number, it:

Prints the number
Says whether it’s even or odd
Says whether it’s positive or negative (kind of obvious here, but still)
Prints its square

Here’s the full example:

numbers = list(range(1, 21))

for number in numbers: 
    print("Number:", number)

    if number % 2 == 0:
        print("- Even")
    else:
        print("- Odd")

    if number > 0:
        print("- Positive")
    elif number < 0:
        print("- Negative")
    else:
        print("- Zero")

    print("- Square:", number * number)
    print("-------------------")

Notes to Self:

Again: indentation is everything in Python. One extra space can cause a logic error.
range() doesn’t include the last number (e.g., range(1, 21) goes up to 20).
Always double-check logic blocks — like when to use elif instead of just another if.