Arithmetic Ā¶
One of the first use cases of Python is as a calculator. This functions just like a calculator on a phone, web, or a fancy Ti_Nspire.
Printing Ā¶
One of the simplest (and most important!) tasks you can ask a computer to do is to print a message.
In Python, we ask a computer to print a message for us by writing
print()
and putting the message inside the parentheses and enclosed in quotation marks.
Below, we ask the computer to print the message
Hello, world!
.
print("Hello, world!")
Hello, world!
The code is inside the box (known as a code cell), and the computer's response (called the output of the code) is shown below the box. As you can see, the computer printed the message that we wanted.
You can use
print
to output text, variables, or expressions for debugging, user interaction, or any other purpose where you need to see the output of your program.
We can also print multiple things at once.
print("Alex is", 20, "years old.")
Alex is 20 years old.
Addition Ā¶
We can add two numbers and get the result by printing.
print(3 + 4)
7
There is no reason to only stop at two numbers.
print(3 + 4 + 5)
12
What about decimals?
print(3.14 + 0.4829209)
3.6229209
Surely it cannot add zero.
print(0 + 0)
0
Oh, it can. Neat.
Subtraction Ā¶
We can also do some subtraction.
print(7 - 2)
5
This still works on decimals!
print(73.92 - 1.3892)
72.5308
Multiplication Ā¶
In Python, a single
*
symbol means multiplication.
print(5 * 6)
30
Oh how I wish I had this when learning the multiplication tables. I also don't have to worry about computing how much to tip.
print(0.2 * 32.4)
6.48
Division Ā¶
In Python, the
/
symbol means division.
I wonder how many slices of pizza each person can have if I share with
3
people.
print(8 / 2)
4.0
Well, I guess not. Maybe next time.
Exponents Ā¶
So far, we have had similar symbol operations for math; however, python uses
**
to mean the exponent.
For example, $2^3$ would be computed in Python as.
print(2**3)
8
Now, sometimes you have to deal with pretty large numbers in scientific notation, like $1.3 \times 10^{4}$. We can use our exponents and multiplication.
print(1.3 * 10**4)
13000.0
I do not technically need to put
(7)
, but it does not hurt.
print(1.3 * 10 ** (4))
13000.0
However, if I want to do something like $1.3 \times 10^{7 * 0.5}$, I definitely need the
()
.
print(1.3 * 10**7 * 0.5) # This is wrong!
6500000.0
print(1.3 * 10 ** (7 * 0.5)) # This is right!
4110.960958218893
It can get really tedious to keep typing
1.3 * 10**2
, so Python has a shortcut to just type
1.3e2
.
print(1.3 * 10**2)
130.0
print(1.3e2)
130.0
Comments Ā¶
What is that
#
doing there?
That is a comment.
You can add text, code, anything into Python code after a
#
and Python will ignore it.
# print(2 * 2) This will not print!
print(3 * 3)
9
We use comments to annotate what code is doing or explaining why. This helps other people to understand your code, and they can also be helpful if you haven't looked at your own code in a while. So far, we have written short code, but annotations become more important when you have written a lot of code.
Once Python sees the pound sign and recognizes that the line is a comment, it is completely ignored by the computer. This is important, because just like English or Hindi (or any other language!), Python is a language with very strict rules that need to be followed. Python is stricter than a human listener, though, and will just error if it can't understand the code.
Math library Ā¶
Python may have a lot of built in calculator stuff, but it does not have everything.
For things like $\cos(\pi)$ or $e^{0.2}$ we need to import the
math
library
.
Do not worry about what a library is yet, we will get there later.
At the moment, you just need to know that you need to tell Python you want to use the
math
library.
We do this by using the
import
statement.
You can get information of what is inside this math library by going to its documentation .
import math
print(math.cos(math.pi))
-1.0
print(math.exp(0.2))
1.2214027581601699
š Exercises Ā¶
Here are some exercises you can do to practice. Open this document in Google Colab and write your Python code in the cells below.
Sales tax Ā¶
If this cute blouse costs $32.45, how much will you pay at the register if sales tax is 6%?
Answer: 34.37
Volume of a cylinder Ā¶
If I have a cylinder with a radius of 0.2 cm and length of 4 cm, what is the volume?
Answer: 0.503 cm 3
Number of atoms Ā¶
Suppose I have 0.3 g of glucose (C 6 H 12 O 6 ) with a molar mass of 180.156 g/mol. How many Carbon atoms are there?
Answer: 6.01 Ć 10 21