Warm up your fingers; in this lesson, we will start coding!

One of the main concepts in programming is variables.

They are your best friends.

You will deal with them all the time.

You will use them to store information.

They will represent your data input.

Let’s say you want to have a variable x that is equal to the value of 5 and then ask

the computer to tell you the value of that variable.

So, we must tell the machine that x equals 5.

And this is how you could do this in Python.

Type x equals 5.

To go through the process of programming, the line that says x equals 5 is called a

command or a program.

This is just a line of text.

To make something out of it, we must execute it.

Only then will the computer carry out operations with it.

Press Shift and Enter (not just Enter), and a variable called x will be created and assigned

with a value of 5.

To be more precise, “equality” in Python and in programming means “assign” or “bind

to”.

Ok, we carried this operation, but we see nothing right now.

How can we ask the computer to show us the output of what we just did?

It would be sufficient to write x and then press Shift and Enter.

And here’s the result – 5.

Great.

As you can see, typing in a single line of code entails a few concepts of programming

simultaneously.

Now, let’s assign the value 8 to a variable we call y. … Alright, Shift plus Enter…

and we can check y.

However, I’ll type capital Y.

Oh!

An error!

This shows us that Python is case sensitive, so pay attention to that.

It matters if you use lowercase or uppercase letters.

An alternative way to execute the instruction that will provide the value we assigned to

y would be to use the print command.

At first sight, it seems redundant as we showed we can just type “y”.

Nevertheless, this command is applied often; you’ll see it in most of the code produced

by professionals.

It complements the logical flow of your instructions.

For instance, if we say “print y”, the machine will simply execute this command and

provide the value of y as a statement, and this is all a programmer must see sometimes.

“Print” exists in Python 3 as well.

Its functionality is practically identical to the one just described for Python 2 with

the sole difference that here you must place the name of the variable within parentheses,

in this case Y.

Then, you can press “Shift and Enter” to execute the code in the cell and see that

you’ll obtain an identical output – the number 8.

The difference stems from the fact that Python 3 treats “Print” as a function, while

Python 2 – rather as a command.

Therefore, from now on, if you are using Python 3, and you see “Print” followed by a name

of a variable, please just add parentheses around the variable name and you’ll be good

to go.

Great!

We hope you found this comparison useful.

Now let’s continue by talking about Python variables.

The last thing I’d like to share with you in this lecture is you can assign a certain

number of values to the same number of variables.

To create the variables x and y, we have to assign two values – say, 1 and 2.

We must separate each of the variables and each of the values with a comma.

The parentheses here are not obligatory, but we use them to improve the readability of

our code.

Now, if I call x or y separately, the computer will correctly give me their respective values.

It is very important that the number of variables on that line equals the number of values;

otherwise, you will get an error message.

See?

Great!

This is a great start to our journey in Python!

When programming, not only in Python, if you say that a variable has a numeric value, you

are being ambiguous.

The reason is that numbers can be integers or floating points, also called floats, for

instance.

Integers are positive or negative whole numbers without a decimal point.

Let’s create x 1 and bind to it the value of 5.

Now, x1 is an integer.

Do you agree?

A specific function in Python can prove this is correct.

It is called “type”.

Within the brackets, we must place the name of the variable whose type of value we want

to verify.

So, in this case, I’ll type x1.

Ok.

Shift plus Enter and the result we obtained is “int”, which indicates the value is

an integer.

The “type” function can also be applied directly to a value instead of a variable.

For instance, if I write “type, open parentheses, minus 6, close parentheses”, Python will

correctly point out that minus six is an integer.

Good.

Now, let’s assign the value of 4.75 to a new variable, x 2.

I would like to check its type; hence, I will use the type function again.

This is a float.

Great!

Floating points, or as you’ll more frequently hear, floats, are real numbers.

Hence, they have a decimal point.

4.75 is such a number; therefore, Python reads it as a float.

Let’s look at two other built-in functions.

“Int” transforms the variable into an integer.

That’s why 4.75 turns into 4.

“Float”, instead, will add a decimal point to the integer value and will turn it into

a float.

Not all variables should assume numeric values.

An example of such type of values is the Boolean type.

In Python, this means a True or False value, corresponding to the machine’s logic of

understanding 1s and 0s, on or off, right or wrong, true or false.

Let’s provide an example with a new variable, x3, which is equal to True.

Right.

The output of the “type” function is ‘bool’, which simply means x3 is a Boolean.

An important detail you should remember is you have to type True or False with capital

letters!

Otherwise, Python won’t recognize your variable as a Boolean and will display an error message.

So, to wrap it up, the two Boolean values a variable can have are True or False, and

they must be written with a capital letter.

Thank you for watching!

Strings are text values composed of a sequence of characters.

Let’s see how we can create a string in practice.

If we ask the machine to display the name George this way, we’ll obtain an error message.

Why?

Because Python assumes George is the name of a variable to which we have assigned no

value.

Here’s the magic trick that will correct this mistake.

Let’s type single quotation marks around the name George, first.

And now, let’s type double quotation marks around it.

You see the output values of these two inputs are the same.

This is how Python displays text results if you don’t use the print command.

Should you use print, the output will be shown with no quotes – you’ll be able to see

plain text.

If we assign this value to a new variable, let’s say x4, we can obtain its output as

we did with the integers and floats.

All right, so that’s it.

If the values you’d like to assign are not numerical, the quotes can come into play!

Assume the variable y is supposed to represent the number of dollars you have in your pocket.

In addition, you would like to ask the machine to print out a statement that says “Y dollars”,

where y is a number.

The proper way to combine the value of y and the string “Dollars” is to use a “plus”

sign, as shown here.

Let’s execute this cell to check if we are missing something.

Apparently, we did not respect the rules of coding in Python.

We cannot put different types of variables in the same expression.

Y is an integer, and “Dollars” is a string.

We can convert y into a string.

“String”, s.t.r., is the built-in function we need.

Analogically to integers and floats, “string” will convert our number into text, and that

will unlock our result.

To summarize what we said so far, Python can automatically guess the type of data you are

entering.

It is within its capabilities to know for sure whether you have assigned an integer,

a float, a Boolean, or a string.

You need not declare the types of variables explicitly, as you must do in some other programming

languages.

Python always knows the type of variable.

What will happen if you type something like…

“I’m fine”?

You’ll need the apostrophe in the English syntax, not for the Pythonic one.

Observe, if you execute the command like this, you will make a mistake.

To avoid that, in such situations, you can distinguish between the two symbols – put

the text within double quotes and leave the apostrophe, which technically coincides with

the single quote between I and M. Now, you are fine.

 An alternative way to do that would be to

leave the quotes on the sides and place a back slash before the apostrophe within the

phrase, and we’ll still obtain the same correct result.

This backslash is called an escape character, as it changes the interpretation of characters

immediately after it.

And what if we wanted to state “press “Enter””, where we put Enter within inverted commas?

Same logic – the outer symbols must differ from the inner ones.

Put single quotes on the sides.

And you obtain the desired result!

Let’s go through a few ways of stating values.

Say you wish to print “Red car” on the same line.

If I write it like this – two words next to each other, separated by a blank space,

I’ll see them attached.

One trick would be to put a blank space before the second apostrophe of the first word.

Let’s see… nice, that looks like the desired result!

Another technique would be to sort of “add” one of the strings to the other by typing

in a plus sign between the two, just as we did with the “10-dollar” example a minute

ago.

Ok.

As your intuition probably tells you, if you print this combination instead, you’ll obtain

the same outcome, but it won’t have the quotes on the two sides.

And… here’s a new trick.

I’ll type “print ‘Red’", and then I’ll put a comma, which is called a trailing

comma, and Python will print the next word, ‘car’, on the same line, separating the

two words with a blank space.

Shift plus Enter… great!

Let’s print the number 3 next to the number 5.

Boom – fantastic!

Here it is.

What will happen if I don’t use the print command and just list a few integers, floats,

and strings separating them with commas?

Python will execute the command as expected but will place the values within parentheses.

Strictly amazing!

Great!

We are making excellent progress!

The next topic on our agenda are arithmetic operators.

The addition and subtraction signs are straightforward to use.

Technically speaking, in the equation you see here, 1 and 2 are called operands, while

in the next one, the operands are 3 and 5.

The plus and minus signs are called operators, and given they also represent arithmetic operations,

they can be called arithmetic operators.

Division is more interesting.

If we want to divide 15 by 3, we will need to use the forward slash sign.

What will happen if we try to divide 16 by 3?

5 again?

Yes, the output was 5 because in Python 2, the quotient is an integer by default.

Mathematically, if we divide the integer 16 by 3, we will obtain a quotient of 5 and a

remainder of 1.

If we use real numbers, or floats, the float 16 divided by 3 will result in a float value

of 5.33.

Therefore, we obtained as a quotient the integer 5 and no information regarding the remainder

of the division of 16 by 3.

This is one of the few substantial differences between Python 2 and 3.

In Python 3, you would immediately get 5.33 as an answer, or a float, because the software

will understand your first number was a float value.

To avoid this, when we use Python 2, we should look for the quotient of the float 16 divided

by 3 and not of the integer 16 divided by 3.

So, we should either transform the number into a float or type it as a float directly.

See?

This is the correct answer.

Now, let’s obtain the remainder of the division of 16 by 3.

How can we make Python produce “1” as an output in this cell?

The operator that can help us is the percentage sign.

I’ll type 16, percentage sign, 3, and when I execute the command, I will obtain the remainder.