Data types operators and expressions

Estimated Time: 20 minutes

What you need to know about data types

Python can store different types of data
The basic types of data you’ll learn about first are:
- Strings
- Integers
- Floats
- Booleans
Python can do different operations based on the data type
- like + to add numbers together

Basic Data Types

Your name, age, date of birth, and photo are different pieces of data. Data, and the variables that refer to them, are represented by different types.

Every programming language has data types, but the built-in types are different from one programming language to another. In Python, we have more than 10 built-in data types. Here are the 3 types we need in this lesson:

int (for integer)
- Represents integer numbers, like 1, 4, or 10
float (a floating-point number)
- Represents floating-point numbers, like 1.0, 4.32, or 10.189
- You might know these as ‘decimal’ numbers or fractions - numbers that have a dot separating the integer part from the fractional part.
str (for string)
- Stores text as character-based data like words, e.g., Hello World

These are called primitive types. Python can represent more complicated data using compound types like List and Dictionary, which are made out of the primitive types. We’ll learn about some of those in later lessons.

Python figures out the type automatically based on some rules:

numbers without a decimal point are treated as ints (like 10)
numbers with a decimal point are treated as floats (like 1.0)
text between quote marks is treated as strings (like "Hello" or '100.5')

There are more rules for other types, but we're skipping them for now.

Video: Data Types

Video Notes

Every value in Python has a type, for example, string, float, and integer. You can find out what type a value is by using the type() function.
Strings are for representing text.
- They look like this: "Kibo School", starting and ending with ", the double quote.
- When you add them together with +, Python concatenates the strings. It sticks them together end to end, like this:
```
school_name = "Kibo"
print("I love " + school_name) # "I love Kibo"
```
- They are called strings because they are a series (a ‘string’) of characters. The string "Kibo" is made of the characters 'K', 'i', 'b', 'o'.
Integers are for representing positive and negative whole numbers.
- They look like numbers: 10, 9019, or -5
- Python works like a calculator. It can do math with +, -, *, / and more.
```
10 + 5 # 15

value = 100
value + 10 # 110
value - 10 # 90
value * 10 # 1000
value / 10 # 10
```
Floats are for representing fractional numbers
- They look like numbers with a decimal point: 10.5, 90.19, or -0.781
- Python stores them differently from integers, so they show something different when you call type on them
TypeError is a common error you get when the types don’t match, like if you tried to add a string and a number.
```
"Hello" + "5" # "Hello5"
"Hello" + 5 # TypeError
```
There are lots more Python types that we didn’t cover. You can look them up by using Google to find the Python documentation.

Operators

Operators are symbols that represent computations like addition and multiplication.

+ performs addition
- performs subtraction
* performs multiplication
/ performs division
** performs exponentiation
% performs remainder (or modulus) operation

What would happen?

Try to guess what each snippet would print out. Then, click the arrow to see an explanation.

print(5 + 10)

It would print 15.

First, python adds 5 and 10, then it does the print.

print(4 + 3 * 2)

It would print 10.

Python uses the same order of operations as school arithmetic, so the * comes before the +.

print(10 ** 5)

It would print 100000.

** is the exponentiation operator, so it's as if Python did 10 * 10 * 10 * 10 * 10.

print(12 % 10)

It would print 2.

The % operation calculates the remainder. 12 divided by 10 has remainder 2.

Expressions

An expression is a sequence of operands and operators, like 15+5, that gets evaluated to a certain result.

Python doesn’t do everything all at once. It runs a program line by line, in order. Within a line, Python has an evaluation order that decides what comes first.

In the below code, the right hand side is evaluated before assignment.

age = 15 + 5
print(age) # 20

The 15 + 5 part of the line is called an “expression”. It’s a part of a line in Python.

Expressions get evaluated before assignment. So in the above code, 15 + 5 is evaluated to 20, and then the value 20 is assigned to the variable age.

Expressions also get evaluated before they get printed out in print():

print(10 / 2) # 5

Python does the 10 / 2 first, then the print()

Math operators and evaluation order

Python uses the same order of operations that arithmetic traditionally uses.

5 + 4 * 3 # 17 (not 27)
6 * 2 ** 2 # 24 (not 144)

This is the order for the math operators:

Parenthesis
Exponentiation (raising to the power)
Multiplication/division/remainder
Addition/subtraction
Left to right to break any ties

You can use parentheses for grouping. They can change the order, or make it more obvious:

5 + (4 * 3) # 17
(5 + 4) * 3 # 27
6 * (2 ** 2) # 24
(6 * 2) ** 2 # 144

Parentheses are also used for calling functions like str() or print(), but it’s usually not that confusing to tell which is which.

Every opening paren needs a closing paren. You can’t do just (5 + 7, it needs to be (5 + 7).

Practice: Working with operators

Solution Code (try for 5 minutes before peeking)

a = 15
b = 7

# Print the sum (+) of a and b (this one is done for you)
print(a + b)

# Print the difference (-) of a and b
print(a - b)
# Print the product (*) of a and b
print(a * b)
# Print the quotient (/) of a and b
print(a / b)
# Print the remainder (%) of a and b
print(a % b)

TypeError and Type Conversion

If you try to add a number to a string, Python will raise a TypeError. It doesn’t know what you want to do. Do you want to concatenate the two, as if they are both strings? Or, add them together mathematically, as if they are numbers? Python refuses to guess.

age = "15" # a string
age + 5 # TypeError, tried to add a string and an int

To solve this error, you can convert between data types.

Turn a string into an int with the function int().
Turn an integer into a str with the function str()

age = "15" # a string
int(age) + 5 # 20
age + str(5) # "155"

Future Proof With Python