How to Use Strings in Python - Python Tutorial for Beginners

[MUSIC PLAYING]

MOSH HAMEDANI: So here we
have this course variable

set to Python programming.

As I told you before,
whenever you work with text,

you should surround
your text with quotes.

You can either use double
quotes or single quotes.

That's more of a
personal preference,

but quite often we
use double quotes.

We also have triple
quotes, and we use

them to format a long string.

For example, if you have, let's
say, a variable message, that

is the message we want to
include in the body of an email.

You can use triple quotes
to format it like this--

Hi, John.

This is Mosh from
codewithmosh.com--

blah, blah, blah.

So that's when we
use triple quotes.

Now we don't need
in this lecture.

So delete.

Let me show you a few useful
things you can do with strings.

First of all, we have this
built-in function in Python

for getting the
lengths of strings.

What is a function?

A function is basically
a reusable piece of code

that carries out a task.

As a metaphor, think of the
remote control of your TV.

On this remote control, you have
buttons for different functions,

like turn on, turn off,
change the channel, and so on.

These are the built-in
functions in your TV.

In Python and many other
programming languages,

we have the exact same concept.

So we have functions
that are built

into the language
and the platform.

You can reuse these functions
to perform various tasks.

So here we can use the
built-in len function

to get the length
of a string, which

means the number of
characters in that string.

Now whenever you want
to use a function,

you should use parentheses.

Now we say we're calling this
function, which basically means

we are using this function.

Now some functions
take additional data,

which we refer to as arguments.

These arguments are
inputs to these functions.

So this len function takes
an input or an argument.

Here we pass our
course variable.

And this will return the number
of characters in this string.

So let's print that
and see what we get.

Run the program.

We get 18 because we
have 18 characters here.

Let's look at another example.

If you want to get access
to a specific character

in this string, you use the
square bracket notation.

So here we add course
square brackets.

To get the first character,
you use the index 0.

So in Python, like
many other languages,

strings are 0
indexed, which means

the index of the first character
or the first element is 0.

So now when we print
this, we'll get p.

Now you can also use a
negative index like minus 1.

What does that mean?

Well, if 0 represents
the first character here,

what do you think
negative 1 represents?

That takes us back to
the end of the string.

So that returns
the first character

from the end of the string.

Let's run this program.

You will see we'll get g.

There you go.

Using a similar syntax,
you can slice strings.

Let me show you.

So I'm going to duplicate this
line and remove negative 1.

Now let's say we want to
extract the first three

characters in this string.

So here we need two indexes--

the start index
colon the end index.

So this will return
a new string that

contains the first three
characters in this course

variable.

That will be p, y, and t.

So the index of these
characters are 0, 1, and 2.

So that means the character at
the end index is not included.

Let's run the program and make
sure we get the right result.

There you go--

Pyt.

Now, what if we don't
include the end index?

What do you think
we're going to get?

It's common sense.

We start from index
0 and go all the way

to the end of the string.

So this will return
a new string that

is exactly the same as
the original string.

Let's take a look.

So we get Python programming.

Now, what if we don't
include the start index

but include the end index.

What do you think
we're going to get?

Once again, it's common sense.

So by default, Python
will put 0 here.

So it will start from the
beginning of the string.

So when I run this program, we
should get Pyt one more time.

There you go.

And finally, as
the last example,

if we don't include the
start and the end index,

this will return a copy
of the original string.

Let's look at this.

So we get Python programming.

Now you don't have to
memorize any of these.

Just remember we
use the len function

to get the length of a string.

We use bracket
notation to get access

to a specific element
or a specific character.

And we use this notation
to slice a string.

[MUSIC PLAYING]

So we have this string
here, Python programming.

Now let's say we want
to put a double quote

in the middle of this string.

There is a problem here.

Python interpreter
sees this second string

as the end of the string.

So the rest of the code is
meaningless and invalid.

How do we solve this problem?

Well, there are two ways.

One way is to use single
quotes for our string,

and then we can
use a double quote

in the middle of the string.

But what if, for
whatever reason,

perhaps for being
consistent in our code,

we decided to use double quotes?

How can we add
another double quote

in the middle of this string?

Well, we can prefix
this with a backslash.

Backslash in Python strings
is a special character.

We have a jargon for that
called escape character.

We use it to escape
the character after.

Let me show you what I mean.

So let's print this course
and run this program.

What's going on here?

We don't have the
backslash because we

use that to escape
this double code

and basically display it here.

So backslash is an
escape character.

And backslash double quote
is an escape sequence.

In Python strings, we have
a few other escape sequences

that you should be aware of.

Let me show you.

So in Python, we use a hash
sign to indicate a comment.

A comment is like additional
note that we add to our program.

It's not executed by
Python interpreter.

So here are the
escape sequences.

You have seen
backslash double quote.

We also have backslash
single quote.

So we can use that to
add a single quote here.

Let's run the program.

Here it is.

Beautiful!

We also have double backslash.

So if you want to include a
backslash in your strings,

you should prefix it
with another backslash.

Let me show you.

So when we run this,
we get Python one

backslash programming.

And finally, we have backslash
n, which is short for new line.

So now if I add a backslash
n here, see what we get.

We get a new line after Python.

So programming will end
up on the second line.

So these are the escape
sequences in Python.

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Here we have two
variables-- first and last.

Let's say we want to print
my full name on the console.

So we can define another
variable, full, set it to first.

Then concatenate
it with a space.

And one more time
concatenate it with last.

Now when we print full, we get
my full name on the console.

Beautiful!

Now this approach of using
concatenation to build a string

is OK, but there is a
better and newer approach.

We can use formatted strings.

So here we can set
full to this string

and prefix it with an f, which
can be lowercase or uppercase.

This formatted string
doesn't have a constant value

like these two strings here.

It's actually an expression that
will be evaluated at runtime.

So here we want to
add our first name.

We use curly braces to print
the value of the first variable.

After that, we add
a space, and then we

add curly braces one more
time to print the last name.

So at runtime, this
expression will be evaluated.

What we have in
between curly braces

will be replaced at runtime.

Now let's run this
program one more time.

We get the exact same
result. Just be aware

that you can put any
valid expressions

in between curly braces.

So earlier, you learned about
the built-in len function.

We can call len here to get
the length of this string.

Let's run this program
one more time so we get 4.

We can also replace last with an
expression like this, 2 plus 2.

Let's run this program.

We get 4 and 4.

So when using
formatted strings, you

can put any valid expressions
in between curly braces.

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In this lecture, we're going to
look at a few useful functions

available to work with strings.

So earlier, you learned about
this built-in len function.

This function is
general purpose.

So it's not limited to strings.

Later I will show you
how to use this function

with other objects.

But in Python, we have
quite a few functions

that are specific to a strings.

Let me show you.

So here, if we type
course., see, all these

are functions
available on strings.

Now, in precise terms, we refer
to these functions as methods.

This is a term in
object-oriented programming

that you will learn about
later in the course.

For now, what I want
you to take away

is that everything in
Python is an object,

and objects have
functions we call methods

that we can access
using the dot notation.

So here course is an object.

We use the dot notation to
access its functions or more

accurately methods.

Let's take a look at a
few of these methods.

We have upper to convert
a string to uppercase.

Now, let's print this
and run the program.

Here is what we get.

Beautiful!

Now note that the methods
that you call here

return a new string.

So the original string
is not affected.

Let me show you.

So print course.

Run the program one more time.

Look.

This is our original string.

So course.upper returns a
new string, a new value.

We can store it in a variable
like course_capital like this.

Now to keep this demo
simple and consistent,

I'm going to revert this back
and use a print statement.

We also have the lower method to
convert a string to lowercase.

We also have title,
which will capitalize

the first letter of every word.

So if our string was like this,
when we call the title method,

we get Python programming
as you see here.

Another useful method
is strip, and we

use it to trim any
whitespace at the beginning

or end of a string.

This is particularly useful when
we receive input from the user.

Let me show you.

So let's imagine the user
entered a couple of white spaces

at the beginning of this string.

When we call course.strip, those
white spaces will be removed.

Take a look.

So note that in the
first three examples,

we have those white spaces.

But in the last
one, it is removed.

So a strip removes the white
space from both the beginning

and end of a string.

We also have lstrip, which
is short for Left Strip,

and rstrip, which is
short for Right Strip.

So it will remove the white
space from the end of a string.

If you want to get the
index of a character

or a sequence of
characters in your string,

you should use the find method.

Let me show you.

So course.find.

So as an argument, here
we pass another string.

We can pass a character
or a series of characters.

Let's find the index of pro.

Run the program.

So the index of pro is 9.

So if you start from 0
here all the way to 9,

this is the index of pro.

Now, as I told
you before, Python

is a case-sensitive language.

So if I pass a capital
P here, obviously we

don't have these exact
characters in our string.

So let's see what we get.

We get negative 1.

That means this string was not
found in the original string.

Another useful
method is replace.

So we call replace.

With this, we can
replace a character

or a sequence of characters
with something else.

So let's say we want to replace
all lowercase p's with j.

With this, we get
jython jrogramming,

whatever that means.

And finally, if
you want to check

for the existence of a character
or a sequence of characters

in your string, you can
use the in operator.

Let me show you.

So print, rewrite an expression
like this-- pro in course.

So this is an expression.

As I told you
before, an expression

is a piece of code
that produces a value.

So this expression checks to
see if we have pro in course.

The difference between this
expression and calling the

find method is that
the find method returns

the index of these
characters in our string,

whereas this expression
returns a Boolean,

so it's a true or false.

Let me show you.

So run the program.

We get the Boolean true.

And finally, we have
the not operator.

And we use that to see
if our string does not

contain a character or a
sequence of characters.

So let's change this
to swift not in course.

When this expression
is evaluated,

what do you think
we're going to get?

Well, we don't have
swift in this string,

so not in will return true.

Let's take a look.

There you go.

So these are the
useful string methods.

Next, we'll look at numbers.

Hi, guys.

Thank you for watching
this tutorial.

My name is Mosh
Hamedani, and I have

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Thank you, and have
a fantastic day!