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Hi again and in the previous lecture we
built this graphical user interface with

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tkinter, but the problem is this does
nothing for now so we press this

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but it doesn't do anything, so what
I'd like to do here is, the final output

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I'd like to have is when I execute this
button, so we have we have an entry here

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we can input a value and I want to
execute this button and get miles here

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in the text area, so miles is like one
kilometer unit is equals to one mile

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times 1.6, so if I execute this I want
something like 16 here to be generated.

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So a very simple program. Note that this
is not one of the real programs that I've

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promised to build in this course. So this
is just to get you up and runing with

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tkinter, so let's close this now and to
have a button do something we need to

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add a command parameter here, so the
command parameter takes a function here

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as argument, as a value and then when you
press that's that button, the execute button

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in this case, the function that you have
here will be executed. So let's say we

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have a function here def kilometers to miles.
Now let's say this function

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for now just prints out some text.
Let's say success for instance because

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you know it's good to before you write
your actual program it's good to use

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print statements to try things out
so that allows you to isolate your problems.

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If something happens here you know that
you can have a problem with a print

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statement, but if you had more
complicated expression here it gets

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harder to know whether the problem
happens in here that you are not

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pointing to the correct function or you
have a problem with your statements,

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so it's good to use simple statements first
like the print statement.

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So you'd go here and
kilometers to miles, that is a function

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and one thing you should keep in mind is
that you don't pass the brackets here,

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so this is not a usual function call.
You are just referencing to the function here

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and let Python take care of the rest.
So the function name goes here and let's

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try this out. Execute and you see that
we got success printed out in here

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Press again success success success,
so it's working.

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However we don't need to print our
success in the command line. We want to

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print out a value in the text area.
Now we need to look at the entry widget

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because series where we are going to get
the value from, so the user enters a value

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in the entry widget and then we
grab that value and then we use that

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value in our function and for this there
is a parameter called text variable

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and that would be equal to a string object
which we have to declare further

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up here, so let's say you want value,
so that's a variable and that'll be equal to

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the stringVar function and then we
point to e1 value, a variable which

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we have just created so this variable
will get the value depending on what the

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user will input in the entry widget.
Then we can use this value whatever we like.

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Let's say we want to print that out.
E1 value and then we also need to add

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something extra here which is
a get method of the stringVar object,

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so this is a special object. Is not a string.
A Python plain string. To get an

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actual string from out of this object
we need to apply the get method, so save

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this and try the script, let's say 10
here, execute and we get 10 printed out

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on the terminal, so we haven't yet
connected this string

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here with the text widget so let's do just
that here. The idea here is that we need

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to insert a value to the text widget and
to do that what text widget has a method

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call insert, so you need to refer to the
text widget that you want. So t1 is our

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text object and then apply the insert method.
And the method gets an argument first

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which is the place where you want to
insert the text. Let's say we want to

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insert at the end of the text widget.
For example let's suppose you are inserting

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many lines of text in your widget and
you have to apply to execute this

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method multiple times and each time if
you put END, you'd enter the new text

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at the bottom of the existing text, so you
are saying put at the end this text.

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E1 value.get.
So the string of value that the user

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will enter in the entry widget, so let's
see how these goes. Execute the function

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and put some text here. You can also put
anything. Hey there. Execute and you get

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the string printed out in a text widget.
All right but we don't want to just

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grab this value and insert it in the text.
We want to first do something with

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this value and then we insert the product,
the output in the text widget so let's

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say we will grab the e1 value.get.
And we will multiply that by 1.6

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and that would be miles, so miles
equals to the value that the user inputs

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times 1.6, so you are asking the user
to input kilometers and 1 mile is equal

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to 1 kilometer times 1.6. actually is
something like 1.606, I don't remember

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the exact value, but you get the idea.
And lastly you'd want

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to pass miles in here, so you want
to insert the miles output value in the widget.

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Save and execute and I expect to
get an error here let's say 10.

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Yes, we got an error and so when you get errors
don't just try to copy this error and

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paste it on Google and try to see what
other people are saying. You may waste a

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lot of time. Instead invest some time and
try to understand this error, so what this

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is saying is a type error. Can't multiply
sequence by non integer of type float.

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So a sequence can be a list, can be a string,
a tuple etc. And Python is trying to

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multiple a sequence with a non integer
which is a float, so the float here is the

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1.6 number and Python is trying to
multiply 1.6 with a sequence

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with this here so this is not a number
because the get method actually grabs

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a string out of a stringVar objects and
a string cannot be multiplied with

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a float number. If this was 2, it was
possible to multiply for example if you

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multiply me, the string me times 2,
you'd get me me, so, but you cannot

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multiply me by one point six because
it doesn't makes any sense. Anyway, so a

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solution to this is you want to convert
the value that the user inputs

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to a float and you do that by adding the
float function, so watch out for the

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brackets here. You see there is an
underline under the bracket and you have

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an underline here, so this means is bracket
it closes in here, so everything looks fine.

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So if we execute again. 10 and execute.
And we get the expected output.

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You can delete this print function.
We don't need it anymore, and I believe that

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was a good start with
the tkinter library.

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And you should not be able to make more
advanced interfaces, however we'll be

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building a real advanced graphical user
interface with tkinter which will

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interact with a database, so it'll be
real world program, and for now I'll just

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hand you an exercise in the next lecture
so that you practice tkinter a little bit,

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and you also get to know with some more
cosmetic aspects, so you will make the

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problem that we built in this lecture
you'll make it more visually appealing

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and you'll make sure you'll get your
hands dirty with tkinter a little bit.

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I'll talk to you later