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In this lesson, I'm going
to show you how you

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can read some text
from a file with Python

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and how to organize this text
so you can use it in your program.

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So I have first created a new Python file
here, read-write.python for this section.

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And then in the same directory here, at
the same level, I have created a file test.

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Okay, this is just the name for the
file, which contains a list of numbers.

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And actually, you can see we
have just one number per line.

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Okay, those are integer numbers
with positive and negatives.

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One thing you can see is that this
file doesn't have any extension, okay?

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You can create a file without any
extension. That's not the problem.

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On Windows, it's going to say that
maybe it's not going to recognize the file,

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but you actually don't need
an extension to create a text file.

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You are going to be able to read it
from Python without any problem.

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So you can create a file,
put it in the same folder here.

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If you want to do that, you
can just create a new file here.

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Don't create a Python file.
Just create a new file, give

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it a name, and that's it,
all from the file manager.

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And now, how we are going
to read that file from Python.

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So I'm going first to write
the code structure, okay?

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And that's going to be the same every time.

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And then I'm going to explain it.

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So with keyword, with-- so open function.

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The first parameter is the
name of the file or the path.

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The second is R for reading,
and then you have as F colon.

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Go back to a new line with indentation.

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And if you want, for
example, to print the entire

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file, you can do print,
and then F dot read.

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So let's actually run that.

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And you can see we have
the content of the file here.

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Okay, all the numbers
you see here are here.

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So that worked.

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And now let me explain that a bit more.

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So this structure you are going
to use it to read from any file.

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Okay, you start with
the with keyword, okay?

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And then open function, okay?

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The thing with file is
that you need to first

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open it, and then you
need to close the file.

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That's very important.

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Here you can see we don't close the file.

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We don't call a close function.

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Why is that?

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Because the with keyword is
going to take care of that, okay?

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So whatever is after
the with, you can be sure

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that you can do whatever
you want with this file.

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And then when it's going to
go out, or if you have an error,

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the with keyword will make
sure that the file is closed.

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So you can open it
again safely the next time.

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So the function open
is going to open the file.

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You need first to provide the path.

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Okay, so this is the path.

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This is directly the name of the file
because we are in the same folder.

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And then you need to provide, so between
quotes, you need to provide the permission.

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What do you want to do with the file?

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Here we just want to read, so
you're going to put the letter R.

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As simple as that.

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And then you have ask keyword and then F.

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F is going to be the variable
you can use inside the with block.

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And this represents actually
the file that was opened here.

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Okay, so you write this and then you
can do whatever you want with the file.

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And now we have F.read,
which is a function you can

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use on a file, which is
simply going to read the file.

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So to read everything
and we just print that.

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All right, and now what if we want, for
example, to read each line separately

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and not just get the
whole text in one block?

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What you can do, I'm going to remove that.

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You can do for line in F.

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So this also is a very
common structure for line in F.

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And let's do print line.

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So for line in F, so the
file that you get here

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is going to iterate through
all the lines of the file.

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So I can run this and you can
see we still have the same numbers.

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But we also have a new line every time.

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Okay, we have an additional new line.

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Okay, so how to get rid of this.

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So this is very common
when you do this structure.

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How to get rid of this?

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Well, line is a string.

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And the thing is that every
time you go to a new line with

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this structure, it's going to
add a new line character.

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So you need to remove that new
line character for each line you read.

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And to do that, you simply do line.rsstrip.

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Okay, this is a function on string.

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And you can do quote and backslash n.

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So actually, what is this backslash n?

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Okay, if I am going to do something print,

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I'm going to do a backslash
n, b backslash n, c.

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Okay, and I'm going to run that.

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And you can see we have
a, b, c each on a new line.

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Okay, the backslash n character
is actually a special character.

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So when you do backslash plus letter,
you usually have a special character.

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And this is simply
going back to a new line.

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So the problem with this
structure is simply that

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you get a new new line
character for each line.

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And the r.sstrip is simply going to
remove it from the end of the string.

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So if you have this string, for example,

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and you use that function, it's
going to remove the last backslash n.

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Okay, so now I'm going to run it like this.

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And you can see we
have each line without any

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additional backslash n
on new line character.

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Great, so now you can open the
file and process each line separately.

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What I'm going to show
you now is about this.

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I'm going to come back
to this file name or file path.

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So you have two ways
to provide the path here.

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Either the relative path,
which is what we've done here.

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So relative is simply that where
is this file relative to that one?

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This is in the same folder, so
you just write the name of the file.

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If this is somewhere else, you
need to change the path, okay?

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So if you create a new folder
and you put this in the folder,

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you need to put the
name of the folder first.

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Now what you can also do is
to provide the absolute path.

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So I'm going to go here and
right click and do copy path, okay?

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And you can see, so
we have the relative path,

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which is that one,
path from content root.

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And we have the absolute path, which is
actually where the file is exactly, okay?

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So see users, my
username, and then PyCharm

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projects, my first
project and the file name.

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So I'm going to copy this
and I'm going to replace it here.

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And using this, I'm going to be
able to open the file the same way.

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But for Windows, we need
to change something, okay?

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If you're using Linux or Mac OS, you
don't need to change anything on the path

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because it's going to use
forward slashes, okay?

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So forward slash is simply like this, okay?

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But on Windows, you have backslashes.

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And as you have seen with the
backslash, and when you use a backslash,

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usually it means that you
have a special character.

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So what we need to do if you want
to use a backslash in a string actually,

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without triggering a special character,
you need to double each backslash.

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So that's what I'm going to do.

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Every time I see a backslash, I
double it with another backslash.

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As you can see here,
you have a recognized

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backslash F, which is
going to do something.

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If I put a backslash here, it's
simply a normal backslash, okay?

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And now I have the absolute path.

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I'm going to run this and
this is going to work the same.

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So you can either provide
the absolute path or the

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relative path, depending
on what is more convenient.

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So now what you can do with this,
well, you can do whatever you want.

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For example, you could
create a number list,

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again, empty number list
before the width structure.

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And then for each
line, you're going to add

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the new line or the
new number in the list.

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Okay, so make sure you also
cast, and the number, so cast this

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to integer float, so you can
make them usable in your list

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when you want to make
computations with numbers.

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All right, so now you can read from a file,

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and you can also see how to
organize the content you read,

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so you can then process
it in your Python code.