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In this course,
you're going to learn to write computer

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programs in the Python
programming language.

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But before we get into that, we need
to know exactly what programming is.

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Fundamentally, programming is
giving a list of instructions for

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a computer to follow.

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In the contest of programming,

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this instructions are sometimes
called algorithms.

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Now computers are really good in following
this instructions very reliably and

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very quickly but not very creatively.

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And we can't just give computers
instructions in English or any other

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natural language that we normally speak
because natural language has ambiguity.

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Words or sentences can have multiple
meanings which computers can't figure out.

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Instead we need to give computers
instructions in a programming language,

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which is a kind of language
that computers can understand

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because they have a formal syntax or
set of rules.

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There are many programming languages that
exist including JavaScript, C++ Java,

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Haskell and many many more.

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But in this course we're going to learn
to use the Python programming language.

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The process of learning programming is
more than just learning the rules of

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the Python programming language.

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It's also about how to breakdown and

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solve problems regardless of
the programming language.

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And I like to think of programming as a
translation process, where the programmer

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translates their goals from natural
language into a programming language.

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For example,

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if I want to write my own version of
the game Wheel of Fortune, then I need to

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translate the rules of the game into an
unambiguous set of instructions written in

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the Python programming language that
tell the computer how to run the game.

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And as you become a programmer, you'll
learn how to come up with strategies, or

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algorithms, for solving problems in
how to translate these strategies

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in the Python code that
a computer can execute.

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Now, all that said, the best way to learn
programming is through practice, so

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let's get started.

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In this course, you'll be able to write
Python codes right in your browser.

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You'll see what are called
active code windows

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that look like this in your textbook.

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Now, most programming courses start off
with what's called a Hello World program

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or a program that prints out Hello World
on the screen when you run it.

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In Python, a program to print
Hello World looks like this.

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In order to actually run this code,
we need to click the Save & Run button.

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When we do that, we'll see an output
window show up to the right here.

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Now to break down what all of this shows,

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we have our Python
source code on the left.

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And we have our output on the right.

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Now, when we click Save & Run what
happens is that there's a hidden Python

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interpreter.

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And it looks at what's in our source code,
and

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prints out whatever any
relevant output is.

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And remember that this source
code is a set of instructions.

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In this case, the source code
is an instruction to print out

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whatever is in quotation marks here,
in this case, Hello World.

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If we wanted to change the set
of instructions, so for

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example, I want to change it to print out,
Hello Michigan.

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Then I need to put it through the
interpreter by clicking Save & Run again,

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and now when I do that,

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you'll see that my output changed
from Hello World, to Hello Michigan.

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If I want to change it back,
Then I need to click Save & Run.

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Now, the Python interpreter typically
tries to run all of the source

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code that we put in this window.

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But it can sometimes be helpful to leave
natural language notes or explanations for

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ourselves or for other programmers
who are looking at the source code.

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Now the Python interpreter
typically tries to run

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all of the source code that we put
into our source code window, but

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sometimes it can be helpful to leave
natural language notes or explanations for

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ourselves or for other programmers
looking at the source code.

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In order to do that,
we have what are called comments.

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In Python, we write a comment
by using the # symbol and

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writing what we want after it.

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When we write a comment, then Python
ignores everything that comes after the #

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symbol, meaning that we can
write whatever we want here.

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And on the next line,
Python will start running the code again.

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So if we wanted to write a comment,
we would need to add a # symbol.

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And what comments do are they tell
the Python interpreter to ignore

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these portions of the source code,
and only to run what's not commented.

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In our case, the only code that actually
runs here is print Hello World.

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Another thing that's worth noting is
that the Python interpreter is not very

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forgiving.

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So recall that when you write source code,
you're giving the computer a set of

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instructions, and
these instructions need to be unambiguous,

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they need to follow the rules of
the Python programming language.

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One of the rules of Python is that
when we have an open parenthesis,

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then we are going to need to
have a closed parenthesis.

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So, let's suppose that
I forget that rule and

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I delete this closed parenthesis,
and I try to run my program.

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What happens is that I get
what's called a syntax error.

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A syntax error is Python saying that it
doesn't understand the rules of what you

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wrote, so it doesn't try to actually
execute what's in the source code window.

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In other words, a syntactic error or
a syntax error is when

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you are not following the rules of
the of the Python programming language.

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In this case, we are not following
the rule that this open parenthesis

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has to be followed by
a closed parenthesis.

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Throughout this course,
we're going to run into syntax errors and

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other kinds of errors, including run
time errors and semantic errors.

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So when we get a syntax error, as we
will many times throughout this course,

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we can fix it by editing the source
code to obey the syntactic rules of

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the Python programming language.

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In this case,
I'm going to add a close parenthesis

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to match the opening parenthesis
that starts out here.

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Now when I click Save & Run again,

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then you'll see that the syntax error
disappears and my program runs again.

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With that, you're already on your
way to becoming a programmer.

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With more practice, you'll better
understand how the Python interpreter

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works, and will be able to write larger,
and more complex programs.

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See you next time.