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Course: Intro to computer science - Python > Unit 1
Lesson 2: Program executionPrint statements and adding values
Evaluate Python expressions that use the plus operator. Add integer, float, and boolean data types, and apply string concatenation to add strings together. Ask the computer to display the result in the console using the print function. Created by Kim Merrill.
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- Is Python Easy? Is it easy to learn?(4 votes)
- Python is a high-level language which means that most of its syntax is similar to basic english. Its a very popular language and easy to learn. Also, it has great community support so you can ask easily ask for help from other python programmers on online forums.(12 votes)
- What if you want it to put 199 and potato on the same line??(2 votes)
- You can make 199 a string as well by putting it in quotation marks. I'm pretty sure later in the course you learn about variables, where you can store 199 as a variable and use a comma to link it to the word potato, like this:
number = 199
print("potato" , 199)
orprint("potato" + "199")
(4 votes)
- Is this course for people above the age of 13??(2 votes)
- No, anyone with the passion can learn Py.(2 votes)
- In the video it was said that float + float = float, but what if we have 1.5 + 1.5? The answer (3) is an integer....(1 vote)
- Where can I find the code editor?
Is it in Khan Academy or an external program?(1 vote)- There is one in Khan academy.(1 vote)
- How can I open the code editor?(1 vote)
- HM. I don't know maybe try the button that says CREATE NEW PYTHON PROGRAM? i don't know tho(1 vote)
- so basically this is also how calulators work or are calulators different(1 vote)
- Is there a way to clear all previous print() statements?(1 vote)
- To clear the output (terminal)
import os
# Clear the terminal screen (Windows)
if os.name == 'nt':
os.system('cls')
# Clear the terminal screen (Unix-based)
else:
os.system('clear')
for Jupiter notebook editionfrom IPython.display import clear_output
# Clear the current cell output
clear_output()
BTW, Web Browsers (JavaScript): If you are working with JavaScript in a web browser(1 vote)
Video transcript
- [Instructor] Programs
manipulate data in the forms of integers, floats,
Booleans, and strings, but how do they manipulate data? Perhaps the most obvious thing we can do here is add values together, but in order to do that,
we'll need the plus operator. In programming languages, operators are symbols that act on values. For example, here we have the value five, which is an integer, the operator plus, and the value two, which
is also an integer. Together, these form an expression. You can think of an
expression like a phrase, it's not quite a sentence but it combines words
together in a meaningful way. When a computer encounters
an expression in a program, it will try and evaluate that expression down to a single value. Think, evaluate, single value. This is similar to humans. When you saw the expression five plus two, you probably did that
calculation in your head and said, "Oh, that's seven." The computer does the same thing. It tries to put every
expression in simplest form, so it's easier for it to work with. So what happens when we add
different data types together? An expression that adds an integer and an integer evaluates to an integer. That makes sense because
if you add one plus one, you're gonna get two,
and two is an integer. You're never gonna get a random
fraction that appears out of nowhere, and you're definitely
not gonna get a string. When we add two floats together, similarly, we get another float. What happens when we add an
integer and a float together? We get a float because if you
add one plus 2.5 together, you get 3.5, and 3.5 is a float because it still has that decimal portion. It didn't go anywhere. You're right that two strings
make a string, but how? Adding strings is called
string concatenation. Concatenating two strings means that we just kind of smoosh them together and then put quotation marks
around the whole thing. So the last character of the
first string goes right up against the first character
of the second string. There's no magic here of inserting spaces or punctuation or anything, so it'll literally just get
smooshed right together. Last few odd cases here. What happens if we add an
in integer and a string or a float and a string? Turns out that's an error. The computer doesn't know
what to do with that. Similarly, I wouldn't
know what to do with that. If you asked me to add a
word and a number together, I'd be like, "Huh, what?" The computer has that
same kind of reaction. It just kind of throws
its hand up in the air and it's like, "I don't
know," and blows up. Last case, what happens
when you add Booleans? Turns out this isn't something
that programmers do often. So we're not gonna talk
about it too much here, but if you're curious, try it out. Let's write our first expressions
in the code editor itself. We're gonna start with the
line 99 plus a hundred. Now, it's probably obvious that this expression
should evaluate to 199, but let's run the program and
see what the computer says. Huh. Nothing. Why isn't it telling us the answer? Turns out computers are
pretty literal creatures. You can think about it like
a stubborn, younger sibling. You're like, "Will you
evaluate this expression?" And the computer's like, "Yes." And you're like, "Okay, well what is it?" And it's like, "Well, you asked me will I evaluate it, and I did. You didn't ask me, will you tell me what this expression evaluates to?" To add that extra instruction
to ask the computer to tell us the result, we need
to use the print function. The print function is the instruction that says, "Display whatever's inside these parentheses in the console." We can print single values, like, we could print eight or
print hello or print 56.34, or we can print the
result of an expression. So if we put an expression
inside the parentheses here, the computer's going to evaluate this expression down to
a single value first, and then print that result in the console. So let's try this again. We have print 99 plus a hundred, and if we run the program
now we see 199 show up because we asked the computer
to tell us the result. I can do this again with
a few other expressions, and you can see each time I hit Run, we see the results of those expression, what those expressions evaluate
to, show up in the console. Some quick things to
pay attention to here. Notice that I put each
instruction on a separate line. The computer gets confused if I tell it to do multiple things at once. I can't put print here and print here. If I try running that, it blows up. Every time we have a new instruction, in this case a new expression
or a new print function, it needs to go on a separate line. Also, note that the output in the console corresponds to the order in which the print functions appear in the program. That's because the computer
is going through the program in order, and the value for
each of these print functions appears on a separate line in the console. So each time it prints a value, it's skipping to the
next line in the console and printing that value
on a line all by itself. Now you try. Open up the code editor and
experiment with evaluating some expressions of your own
and printing the results.