Writing to Files | Python | Tutorial 29

INSTRUCTOR: Hey, welcome
to Giraffe Academy.

My name is Mike.

In this tutorial, I
want to talk to you

about writing and appending
to files in Python.

So one of the cool
things about Python

is it allows you to work
with external files.

So I could have an
external text file,

and I could actually completely
read all of the information

in it.

I could parse through it
and use that information

to do certain things.

But in addition to reading a
file, I could also write a file.

And that's what I want to
talk to you guys about today

is writing new files and
appending onto existing files.

Over here, I basically just
have some code written out.

And this essentially
just reads information

from this employees.txt file.

So you can see over here, I'm
specifying the mode, which is r.

And that stands for read.

And then down here,
I'm just reading

all of the contents of the
file and spitting it out

on the screen.

So I'm going to click the
Play button over here.

And you'll see
that this executes.

So it's printing out all of the
lines of code in our text file.

So over here, I'm in
this employees.txt file.

And it just has all
this information,

like employees in an office.

But let's say that I wanted to
add another employee onto here.

Let's say that a new
employee joined our company,

so we wanted to add
them onto this list.

Well, I can come over here
to my app dot Python file.

And instead of
reading from the file,

I want to append it to the file.

So I want to say a.

And appending to
the file basically

means that you're adding some
text at the end of the file.

So wherever the
file ends, you're

just going to add
some text onto there.

So what we can do is we can
actually add another employee

into the file.

So instead of printing
something out,

I'm actually just going to
say employee_file.write.

And when I say
employee_file.write,

I'm going to be able to
write something to the end

of the file.

So I can basically just
write whatever I want.

So why don't we add
in another employee

into our employees.txt file.

So we can add in another
employee, why don't we say Toby.

And he's going to be
in human resources.

So now when I run
this program, it's

going to add Toby
- Human Resources

onto the end of the file.

So I'm going to run my program.

And you'll see that
nothing shows up

down here in the console.

But if I go over to
my employees.txt file,

all of a sudden, we have
a new entry over here.

It's Toby from human resources.

So I was able to append a line
onto the end of this file.

But here's the thing.

You need to be
careful when you're

writing to files
because you can actually

mess up a file very easily.

For example, I already added
Toby here into my file.

But if I was to run
this program again,

you'll see that over here
in this employees.txt file,

it went ahead and
added Toby again.

So it added this
employee here again.

And also, you'll notice
that in this case,

this employee didn't
go on to the next line.

I accidentally ran my file
again, and all of a sudden,

it messed up this
file over here.

And so appending, you
really need to be careful.

Because if you accidentally
run your file again

or if you append something on,
something wrong to the file,

it's permanent.

It's getting saved
inside of the file.

So I want to talk to you guys a
little bit more about appending.

Another thing we could do.

Let's say we wanted to
add another employee.

And you'll notice over here
in this employees.txt file,

when I appended it
on again, it got

appended to the end
of the existing line.

So the first time, I
had a new line there.

But if you don't have a new
line at the end of your file

and you want to add
a new line, you're

going to have to add
some special characters.

So let's add another employee.

And we'll call her Kelly.

And let's just say Kelly
is in customer service.

So Kelly is going to
be in customer service.

And if I want to
add this employee

onto the end of the
file, in a new line,

I'm going to have to put a new
line character in front of it.

So I can say
backslash n, and this

will append this entry into
the file with a new line, so

on a new line.

So now when I run
this, you'll see

we get Kelly from customer
service on her own line.

So you want to make
sure that you're

aware of these special
characters that you can use.

They call them
escape characters.

And anytime you're
adding on to a file,

you want to make
sure that you're

adding on exactly where
you want to add on.

So in addition to
appending to a file,

I could also just
overwrite a file,

or I could write an
entirely new file.

So since we already
have this open,

instead of appending
to the file,

why don't we just write a file.

So I'm going to use this w.

And now, if I say
employee_file.write,

because I'm using w and I'm not
using a, it's actually going

to override the entire file.

And it's only going to
put this inside the file.

So when I run this and we go
over to this employees.txt file,

you'll see we only have one
line inside of this file now.

It's just Kelly -
Customer Service.

That's because I
was using w, not a.

And when you use w, It's
just overwriting everything

that's in that existing file.

You can also use w
to create a new file.

So over here, I could
say employee_file

is equal to employees1.txt.

And now what's going to
happen is when I run this,

it's going to create
another file for me.

So I'm going to run this.

And you'll see over
here in my file browser,

we have this new
file employees1.txt.

So if I open this up, it
has exactly the same stuff

as in this employees file.

But it basically created
a new file for us.

And so a lot of
times you're going

to want to create a new file.

And you can use
different extensions too.

So if I wanted to create a web
page, I could say index.html.

And I could also add in
some HTML code in here.

So if you don't understand
HTML, don't worry about it.

But if you do, I could
put a paragraph in here,

another paragraph
like, this is HTML.

Basically, HTML is
like a web page.

And the point I'm
trying to make is

that you could write out a
web page inside of Python

by doing something like this.

So now when I play this, we
get this index.html file,

and it has some
HTML inside of it.

So that's one way that writing
to files can be really useful.

You can overwrite
an existing file.

You can write a new
file and create it,

or you can append on
to the end of a file.

And there's tons of applications
for writing to files.

And Python's a great language
for working with reading,

writing, and doing all
that stuff with files.

Hey, thanks for watching.

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