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Iteration, aka repeating, is a solution for tasks that need to be done over and over again.

Instead of writing dozens of lines of code for the same purpose, we can simplify it and shorten it to just a couple of lines. This way the code is both easier to read for the other programmers (fellow people hehe) and faster to process for the computer.

Also, simpler code reduces errors rate.

Examples of iterations are loops.

Looping means repeating something until a particular condition is satisfied. 

Python has 3 Basic Loops:

For Loop - used when we know number of iterations (repetitions) in advance.

While Loop - for situations where the number of iterations is unknown beforehand. 

Nested Loop - using one looping statement inside another looping statement.

For loop is used to execute the same instruction over and over again, a specific number of times.

for i in range(5):     print(“Hello!”) Output: Hello! Hello! Hello! Hello! Hello!

In the first line, we declared how many repetitions are needed. In the second line, we wrote what should be repeated a given number of times. In this case, we asked Python to print the string “Hello!” 5 times.

Basic structure of the for loop:

for i in range(5):     print(“Hello!”)

for - a keyword that signals that “for loop” is starting.

i - internal variable name which is keeping the counter value. Stands for “iteration”. We can read the whole line as “for 5 iterations/repetitions, please do the following:” For every loop, the 'i' variable increases by 1 because it's the counter. 'i' doesn't have to be 'i', we can switch it to another letter or another word, that are python approved for this (for example, you can’t use name of defined function instead of 'i').

#Loop using "unicorn" as internal variable, instead of "i" for unicorn in range(10): print(unicorn) #still works!

  in range() - represents the list of numbers we are looping through (number of time the iteration is running). Python starts the counter from 0. It means that range(5) -  will give a sequence of 5 numbers: 0, 1, 2, 3, 4 range() function has 3 parameters(start, end, steps), default values for start is 0 and step is 1. When we write range(5), we only give one parameter, and the function still works, because Python reads it as range(0,5,1) and the sequence starts with 0, increases by 5 counts, with step between each number being 1, by default.

We can change the parameters: range(1,20,3) this would result in iterations that starts from 1, goes up by 3 steps with the upper limit of 20: 1, 4,7,10,13,16,19.

Example: #print every 2 numbers (evens): for i in range (2, 10, 2):     print(x) output: 2 4 6 8 (!) output does not include 10 because 10 is the upper limit (result only includes number under 10)

: adding a colon sign in the end of the first line is mandatory, otherwise an error will occur.   Finally in the next line, we start writing the instruction, that is supposed to be repeated. This part isn’t starting right away, it should be indented. Indentation is the blank gap at the beginning of lines. Normal indentation is 4 spaces/tab long. Python would recognize 2 spaces or 4 spaces as an indentation, but 4 spaces length is more agreed upon and is used more wildly.

tip: How to write an instruction to get output of a list that starts from 1 instead of 0, accompanied by a string:

Programs use input to do certain work, and in order to receive it from another user, we can use the input function.

The input() function always turns the user input into a string, no matter which type of data was originally put into it.

Example:

cost_of_living=input() #user may write down an answer print(type(cost_of_living)) #to specify the data type of the input user has given

answer: <class 'str'> = string

But! You can't do math with strings, so sometimes we need to convert existing data type of a value.

cost= input() #default data type is a string cost=int(cost) #converts into integer cost=float(cost) #converts into float cost=str(cost) #back to string

Side notes: 1. You cannot convert any type of value to an integer or the float, only numeric values!

cost= "one hundred" cost=int(cost) #would result into an error

while:

cost= "100" cost=int(cost) #would convert string into an integer, as desired

2. Another important thing to remember, is that when we are creating a value as an integer, we use quotes "".

But in order to convert a variable into a string, we have to use a function str().

Unlike strings, numerical values are not quoted with quotation marks:

price = 30

Tip:

Big numbers can be written in a more readable way:

thousand = 1_000

print(thousand)

Output: 1000

million = 1_000_000

print(million)

Output: 1000000

a_really_long_number = 1_000_000_000

print(a_really_long_number)

Output= 1000000000

This way, it would be less confusing for a person dealing with the code!

Numbers can be used to perform some calculations and operations.

Examples:

Operation: Output:

print(110) 110

print(8 + 2) 10

print(10 - 5) 5

print(5 * 3) 15

print(10 / 5) 2.0

Float division: (10 / 5) would give a float number, meaning a number with digits after the coma (like 2.0)

Integer division: using division sign twice (10//5), would give an integer (like 2), without digits after the coma.

Exponentiation: 2**3 = 2*2*2, 5**3=125

👀 Details matter:

num1 = 10

num2 = "10"

Python recognizes num1 as a number and num2 as a string.

It would perform commands differently because of this:

print(2*num1) Output: 20

print(2*num2) Output: 1010

Another example:

print(2*"3+7") Output: 3+7 3+7

print(3+7) Output: 10

Python has two main data type groups:

1) Premitive data type:

Examples: String, Integer, Float, Boolean

2) Non-premitive data type:

Examples: List, Tuple, Array, File, Set

Let's start with strings 💕

Text data is called a string. Example:

"Wassup?"

But although string is usually presented as a text, it's better to consider it as a "string of characters". Examples of what is a character and how it can be presented as a string in python:

"Hi!", "19", "Hello", "A", "🐈".

Although examples above were not only letters, but also a number and an emoji, putting them inside the quotation marks makes python see and use those as strings.

" " is also a string, containing a space 🫡

In Python, you can use single ' or double " quotation marks to define a string. But! You need to stick to one format per string. If quotes aren't matching, you are in trouble :)

Examples:

✅️ "HELLO"

✅️ 'HELLO'

A name doesn't hold a value, but only refers to it.

In python (at least), variable has a name, a value and a data type.

Name of the variable is written on the left, value is written on the right, like this:

candy = "Oreo"

[name = value]

To connect the name and the value of the variable, use equal sign "=".

Additional gratitude to Rain, who explained:

One can think of a variable as a sticky note.

A sticky note can only be stuck on one object at a time, but it can be stuck on different objects at different times, and many sticky notes can be stuck on the same object at the same time.

More info:

What I know now?

Print command is used to make my program display a certain message.

Example:

print("Hi! My name is Zhanna and I'm discovering python")

Printing text requires using (" ") structure.

Printing numbers only needs ( ) structure.

Example:

We are starting with python.

Every day I'm going to learn something new.

The knowledge is going to grow and I'll eventually need an easy library of my own to remind me of something I've learned - this is gonna be it ✨️