Lesson 18

Module 1 summary: First steps

After this lesson: You'll go over everything from Module 1 - print, calculating, text, variables, errors and reading input - and put it together in tasks.

Video

The video for this lesson is coming soon.

Explanation

Well done, this is the end of the first module! 🎉 There's nothing new in this lesson. We'll go over everything you already know - topic by topic - and at the end there are tasks that put it all together.

What you already know

Lessons	Topic
1, 2, 6, 8, 9	`print`, comments, `sep` and `end`, special characters
3, 5, 10	calculating: `+ - * / // % **` and the order of operations
4	whole numbers, numbers with a dot and text
2, 7	text: joining with `+` and repeating with `*`
11, 12	variables and changing their value
13	errors and their messages
14, 15, 16, 17	`input()`, `type()` and changing types with `int()`, `float()`, `str()`

1. Printing: print

print("Hi") prints text, and print(2 + 3) the result of a calculation.
print(a, b) prints several things on one line, with a space between them.
sep="..." changes what goes between, and end="..." what goes at the end.
A line starting with # is a comment - a note for people. Python skips it.

Recap: print

Each line recalls one thing from the print lessons.

Code

1# a comment - Python skips it
2print("Hi!")
3print("Ala has a cat.")
4print("Bajtek likes coding.")
5print("I am", 10, "years old")
6print(1, 2, 3, sep="-")
7print("A", end="")
8print("B")

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What does print(1, 2, 3, sep="") print?

2. Calculating

Sign	What it does	Example
`+ - *`	adds, subtracts, multiplies	`7 * 3` is `21`
`/`	divides (result with a dot)	`7 / 2` is `3.5`
`//`	divides without the remainder	`7 // 2` is `3`
`%`	the remainder of division	`7 % 2` is `1`
`**`	power	`2 ** 3` is `8`

The order: brackets first, then **, then * / // %, and + - last.

Recap: operations

The same two numbers, different operations.

Code

1print("Adding: 7 + 2 =", 7 + 2)
2print("Subtracting: 7 - 2 =", 7 - 2)
3print("Multiplying: 7 * 2 =", 7 * 2)
4print("Dividing: 7 / 2 =", 7 / 2)
5print("Dividing without the remainder: 7 // 2 =", 7 // 2)
6print("The remainder: 7 % 2 =", 7 % 2)
7print("Power: 7 ** 2 =", 7 ** 2)

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What does print(2 + 3 * 2 ** 2) print?

What does print(365 // 7, 365 % 7) print?

The last digit

It'll come in handy in the tasks! The remainder of dividing by 10 is the last digit of the number.

472 % 10

1/2 · click the arrow - Python works out the next part

3. Text

"Ala" + "cat" joins texts: "Alacat".
"ha" * 3 repeats text: "hahaha".
The text "5" is not the number 5! "5" + "5" is "55", and 5 + 5 is 10.

Recap: text

Code

1print("Ala" + " " + "cat")
2print("ha" * 3)
3print("5" + "5")
4print(5 + 5)

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4. Variables

points = 10 puts a value into a box labelled points.
points = points + 5 - Python first works out the right side (10 + 5), then puts the result into the box.

Recap: variables

📦 points

⭐…

Code

1points = 10
2print("Points:", points)
3points = points + 5
4print("Points:", points)
5points = points * 2
6print("Points:", points)

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What will this program print?

x = 3
x = x * 2
x = x + 4
print(x, x % 4)

5. Errors

Error	What it means
`SyntaxError`	badly written code (missing bracket or quote)
`NameError`	no such name (a typo)
`TypeError`	text and a number don't fit together
`ValueError`	`int()` got text that isn't a number
`ZeroDivisionError`	division by zero

We read the message from the bottom: the last line says which error it is.

Which error does Python show for print("2" + 3)?

6. Reading input

name = input() reads one line as text.
We read a number in two steps: n_str = input(), then n = int(n_str).
float() turns text into a number with a dot, and str() turns a number into text.

Example: name and age

Type a name 🧒 and press Enter ⏎, then an age 🎂 and Enter ⏎ again. The name stays text, and the age becomes a number.

Code

1name = input()
2age_str = input()
3age = int(age_str)
4print("Hello,", name + "!")
5print(name, age + 1)

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The input has two lines: 10 (sweets) and 3 (children). What does the program print?

sweets_str = input()
sweets = int(sweets_str)
children_str = input()
children = int(children_str)
print(sweets // children, sweets % children)

The last digit of a number

Type any number 🔢 (e.g. 472) and press Enter ⏎ - the program prints its last digit.

Code

1number_str = input()
2number = int(number_str)
3last = number % 10
4print("Last digit:", last)

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Example: digits of a number

Type a two-digit number 🔢 (e.g. 47) and press Enter ⏎ - the program prints the tens digit, the units digit and their sum.

🔢 number:?

Type a two-digit number on the screen and press Enter - you'll see it built from blocks.

Code

1number_str = input()
2number = int(number_str)
3tens = number // 10
4units = number % 10
5print("Tens digit:", tens)
6print("Units digit:", units)
7print("Digit sum:", tens + units)

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How to approach a task - a 5-step plan

Read the statement and find: what's in the input, and what has to be printed.
Look at the example - are the numbers on one line or several? What's the format of the answer?
Read the data into variables with good names.
Calculate the result - think which operation fits (+, *, //, %...).
Print exactly what the task asks for - with no extra words. Run it on the example and compare.

Example: a clock

Type a number of seconds ⏱️ (e.g. 135) and press Enter ⏎ - the program turns them into minutes and seconds. See the whole plan in one program.

⏱️ All the seconds:?

minutes = ? // 60

left = ? % 60

Type a number of seconds on the screen and press Enter - you'll see how many minutes that is.

Code

1# 3. read the data
2seconds_str = input()
3seconds = int(seconds_str)
4# 4. calculate
5minutes = seconds // 60
6left = seconds % 60
7# 5. print
8print(minutes, "min", left, "s")

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Presents for the children 🎁

Type the number of presents 🎁 (e.g. 47), then the number of children 🧒 (e.g. 9). Press Enter ⏎ after each number. The children can't be 0 - you can't divide by zero.

👜 in the sack: ?

Type the number of presents and press Enter.

Code

1presents_str = input()
2presents = int(presents_str)
3children_str = input()
4children = int(children_str)
5per_child = presents // children
6left = presents % children
7print("Each child gets:", per_child)
8print("Left in the sack:", left)

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How many coins? 🪙

Type an amount in zloty 💰 (e.g. 18) and press Enter ⏎ - the program pays it with as few 🪙 5, 2 and 1 zloty coins as possible and says how many of each coin there are.

💰 To pay:?

5 zlfives

2 zltwos

1 zlones

Type an amount on the screen and press Enter - you'll see which coins pay it.

Code

1amount_str = input()
2amount = int(amount_str)
3fives = amount // 5
4rest = amount % 5
5twos = rest // 2
6ones = rest % 2
7print("5 zloty coins:", fives)
8print("2 zloty coins:", twos)
9print("1 zloty coins:", ones)

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Remember

print prints, sep and end change the spacing, # is a comment.
Calculate with + - * / // % ** - remember the order of operations.
A variable is a box: x = x + 1 first calculates, then stores.
input() gives text - you get a number with int().
Read the statement and the example, read the data, calculate, print only what the task asks for.

Before you submit

Run the program on the example. Then think about other data: what if the number is 0? What if it's very large? The judge tests different cases, not just the example.

That's all of Module 1! Now the tasks - each one combines a few topics. Run your solution on the example and compare the output. Good luck!

Tasks from the video

We solve them together in the video - pause it and try first on your own.

1A greeting 2Calculator 3Rectangle 4Stopwatch 5Candies 6Shopping 7The last two digits 8Digit sum 9Square and cube 10Name and age

Practice tasks

Try to solve them without the video. Stuck? Every task has hints and an editorial.

11A reversed number 12Cinema tickets 13Average of two marks 14Hours, minutes, seconds 15Echo many times 16A kitten with a name 17A path from two words