Data Types

3. Data Types#

Data types in Python link values (or data) with methods that define what operations can be performed on this data. The choice of a data type determines what actions are possible and how they are implemented.

Python offers many different data types. To begin, we will focus on two fundamental types: Numbers and Strings.

3.1. Numbers#

Working with numbers in Python is very intuitive and behaves similarly to a calculator. Python differentiates between Integers (int) and Floats (from the term „floating point number“). Integers are whole numbers (e.g., 5), while Floats are decimal numbers (e.g., 5.01).

Note: Floats are not exact representations of real numbers due to rounding performed by computers for floating-point numbers.

3.1.1. Examples:#

>>> 5
5

>>> 5.01
5.01

Handling signs:

# Positive
+5  # 5

# Negative
-5  # -5

And basic arithmetic operations work as expected:

# Addition
5 + 7  # 12

# Subtraction
5 - 7  # -2

# Multiplication
5 * 7  # 35

# Division
5 / 2  # 2.5

Note: Division in Python always returns a float, even if the result is a whole number:

print(type(5 / 1))

Output:

<class 'float'>

This example also shows that you can check the data type in Python using type().

3.1.2. Advanced Arithmetic Operations:#

# Integer Division
5 // 2  # 2

# Modulo (remainder of a division)
5 % 2  # 1

# Exponentiation
10 ** 2  # 100

3.2. Combining Print Statements and Arithmetic Operations#

Multiple arithmetic operations can be chained and displayed using the print() function:

print(22 * 27 * 7 / 2)

Output:

2079.0

Parentheses can also be used:

print((22 * 27 + 12) / 2)
print(22 * 27 + 12 / 2)

Output:

303.0
600.0

Parentheses can also improve code readability, even when they are not mathematically necessary:

print((22 * 27 * 7) / 2)  # perfectly fine!

Other common number operations:

# Integer Division
5 // 2  # 2 (this is NOT the same as rounding!)

# Modulo
5 % 2  # 1

# Exponentiation
10 ** 2  # 100

3.3. Strings#

Strings are sequences of characters and are defined using either ' or ".

>>> "5 + 7"
'5 + 7'

>>> "Whatever you want to type. 123*..."
'Whatever you want to type. 123*...'

3.3.1. Quiz: Which of the following statements does NOT return an error?#

>>> "five" + "five"

>>> "five" + 5

>>> 2 * "five"

>>> "five" - "ive"

(Try them out!)

3.3.2. Basic String Operations#

Python provides a variety of functions for processing strings. Here are some basic examples:

Strings can be concatenated (added together):

print("Take this!" + " And that!")

Output:

Take this! And that!

However, strings and numbers cannot be concatenated without explicit conversion:

"100" + 5  # => TypeError

That makes sense. But wait! How does Python know whether something is an integer (int), a float, or a string (str) if we haven’t defined it anywhere?

3.4. Duck Typing#

Python uses a principle called duck typing, where the data type is assigned automatically based on the given values (unless explicitly defined otherwise). Duck typing is named after an old saying:

„When I see a bird that walks like a duck and swims like a duck and quacks like a duck, I call that bird a duck.“ (Wikipedia).

3.5. Changing Data Types#

There are situations where we explicitly want to change a data type, for example, from float to int:

print(5 + int(7.00001))  # 12

Output:

12

Be careful! This is not rounding but truncating the decimal part:

>>> int(12.9)
12

(If rounding is needed, use int(round(12.9)).)

Numbers can also be created from strings:

>>> 5 + int("19")
24

But don’t expect magic here. Python only recognizes obvious numbers in strings, not something like:

int("seven")  # => ValueError: invalid literal for int() with base 10: 'seven'

Conversely, we often want to convert a number into a string:

>>> str(5) + "19"
'519'

This is frequently done to output a string:

print("7 + 5 = " + str(7 + 5))

Output:

7 + 5 = 12

A more common and convenient way to combine strings and numbers is using f-strings. These are marked with f"..." before the quotation marks. Within f-strings, values—whether numbers, strings, or other data types—are automatically converted to strings if placed inside curly braces. For example:

print(f"This is {8} times better than that.")

Output:

This is 8 times better than that.

We’ll use this frequently in practice.
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