Reading Files | Python | Tutorial 28

INSTRUCTOR: Hey, welcome
to Giraffe Academy.

My name is Mike.

In this tutorial, I
want to talk to you

guys about reading from
external files in Python.

Now, a lot of times
in Python, you're

going to want to read from files
that are outside of your Python

file.

So you might want
to read information

from a text file, or a
CSV file, or an HTML file.

And you can actually use
something called the Python read

command.

And it will allow you to
read a file that is stored

outside of your Python file.

So you can use these
files to get information,

or you can parse
through different files

and do different things.

So I'm going to show you guys
the basics of reading files,

opening files, closing files,
doing all of that stuff.

Over here, I have this
file called employees.txt.

And it basically just lists out
a bunch of different employees,

like these could be employees
in an office or whatever.

So it's just listing out
all of this information.

So let's say that
inside of my app

dot Python file, I wanted
to read the employees

inside of that file.

The first thing I
have to do is actually

open that file
from inside Python.

So I can use a special
command called open.

So I can say open.

And then in here, I can
type in the name of the file

that I want to open.

So this is either going
to be a relative path

of the file, an absolute
path to the file,

or just the file's name, if both
files are in the same directory.

So in my case, app dot
Python and employees.txt

are in the same folder, like
they're in the same directory.

So I can just type out
the name of the file.

I can just say employees.txt.

And then I want to put
one more thing inside

of this open function.

And it's going to be the mode
that I want to open the file in.

So you can actually open files
in a couple different modes.

And the first mode
is called read.

So I can just put an r here, and
that's going to stand for read.

And this basically
means that I only

want to read the
information inside the file.

I don't want to modify it.

I don't want to change it.

I just want to read it.

I just want to see
what's in the file

and do some stuff
with that information.

Another mode it's called write.

So I can type in this w.

And writing basically means
that you can change the file.

You can write new
information, you

can change existing information.

There's another one called a.

And a stands for append.

And this basically means that
you can append information

onto the end of the file.

So you can't modify any of
the information in the file.

You can't change any
of the information,

but you can add new information.

And there's one more,
which is r plus.

And this basically
means read and write.

So this will give you all the
power of reading and writing.

So in our case, we're just going
to be working with regular r.

So we're going to be
reading from the file.

Now this open function will
essentially just open the file.

So it's going to go over to that
file inside of our file system,

open it up, and it'll allow
us to read through it.

But generally, we're going to
want to store this opened file

inside of a variable.

So I can create a variable.

And we can just call
it employee_file.

And I'm just going to set it
equal to this open function.

So now the open employees.txt
file and all the content inside

of it is stored inside of
this employee file variable.

Now whenever you open
a file, you always

want to make sure that you
close the file as well.

So just like we have
this open command,

we also have an close function.

So I can come down here and
say employee_file.close.

And this is essentially just
going to close the file,

so we're no longer going
to be able to access it.

And generally, it's a good idea.

Whenever you're
opening up a file,

you want to also
make sure that you're

closing the file at some point.

So generally, once
you're done reading it,

you can just close it.

So that's how we can
open and close a file.

Now let's talk about how we can
get information from the file.

There's no point in having
the file there if we

can't figure out what's in it.

So there's actually a
few different functions

that we can use on
this employee file

to figure out
what's inside of it.

And I'm going to show
you guys some of those.

So I'm just going to
make a print statement.

And inside this print
statement, we'll

basically just print out some
information about the employee

file.

So the most basic
thing we can print out

is just the entire
contents of the file.

But before I do that,
I want to show you

guys how you can check to make
sure that a file is readable.

So before we do anything
else, generally, it's

a good idea to make sure that
it's possible to read this file.

And there's a function
inside of Python we can use,

called readable.

So I'm just going to type
out employee_file.readable.

And this is going to
return a Boolean value.

And it's going to
tell us whether or not

we can read from this file.

So I'm going to run my program.

And you'll see down here,
we get a value of true.

And that's because we set
the file with a read mode.

So it's in read mode,
we can read from it.

If I was to put a w
here, so if I put write,

now readable is
going to be false

because we can no
longer read the file,

we can only write to the file.

So I'm going to change this back
to r so we can just read it.

So once you've figured
out whether or not

the file can be read from,
let's actually read it.

So there's another function
called employee_file.read.

And this is basically just going
to spit out all the information

in the file.

So when I run the
program, it's just

going to spit out all of this
information, all the information

that was in that file.

I can also come
down here, and we

could read an individual
line inside this file.

So I can say
employee_file.read line.

And what this is
going to do is it's

going to read an individual
line inside of this file.

So now when I run
this program, you'll

see it's just reading that
first line in the file.

And this read line function
is actually just reading

the first line, and then it's
basically moving a little cursor

onto the next line.

So if I was to copy this line
of code and then print it again

down here, I'm saying
employee_file.readline.

So it's going to
read the first line.

And then when I
say it again, it's

going to read the
line after that.

So this is actually going to end
up printing out the first two

lines in the file.

So when I run this
program, you'll

see we print out Jim -
Salesman and Dwight - Salesman.

So if I was to do
this multiple times,

I could technically print out
every line inside of this file.

And you can see we can do that.

And so that can be pretty useful
for reading multiple lines

in a file.

But there's actually
another function

that is better at doing that.

And we can say, instead
of employee_file.readline,

we can say .readlines.

And what this is
going to do is it's

going to take all of the
lines inside of our file

and put them inside of an array.

And so now when
I print this out,

you'll see we have
this array down here.

It says Jim - Salesman, that's
the first item in the array.

Dwight - Salesman is the
second item in the array.

It's basically taking each
line and putting it inside

of an array.

So if I wanted to
access a specific line,

I can just refer to it by
its index in the array.

So if I said 1, now
this is going to give us

that Dwight - Salesman line.

Because that is at index
position 1 inside of the array.

You can also use this readlines
function with a for loop.

So I could come up here
and create a for loop.

I'm just going to
say for, and we'll

say employee in employee_file.

And then for each employee, we
just want to print them out.

And actually, sorry, we have to
put employee_file.readlines up

here.

And so now this will loop
through all of the employees

in this
employee_file.readlines array.

So we can actually just print
out the individual employee.

And now this will print
out all the employees

inside of that file.

So it's basically printing
out each line in the file.

And that can be pretty useful.

So you can use all of these
different functions read,

readline, readlines, readable.

There's a bunch of
these different things

that we can do to get
information from a file.

And so there's a
lot of cases where

you're going to want to be able
to parse through information

in a file.

And this is a
awesome way to do it.

So just to recap, whenever
you want to open a file

and read from it, you can
just use this open function,

type in the name of the file and
then the mode, which in our case

is going to be r.

Then you can do all
sorts of stuff with it.

And you always want to
make sure that you close it

when you're done.

That's just good practice.

So that's the basics
of reading from files.

And hopefully, you guys can
use this in some way, shape,

or form in the future.

Hey, Thanks for watching.

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