Variables and Data Types

In Python, we don't need to declare a variable's type (like int or char in C).
Python is dynamically typed, meaning it figures out the type of data based on the value we assign to it (variable = value).

Dynamic Typing Vs. Static Typing​

If you are coming from C, you might be used to writing int a = 5;. In Python, we just write a = 5. We can even change the type of data a variable holds later on, though it's usually better to keep it consistent.

Use type(variable) to check what kind of data is currently stored.

a = 10      # Initially an integer
print(type(a))

a = "Ten"   # Now it's a string
print(type(a))

<class 'int'>
<class 'str'>

Numeric Types​

Python's int and float types handle most scenarios automatically.

• Integers (int): Whole numbers of arbitrary precision.
• Floats (float): Double-precision floating-point numbers.
• Complex Numbers (complex): Used for scientific computing, using j for the imaginary part.

x = 10
large_number = 10**100 # Googol
price = 19.99
z = 3 + 4j # Magnitude: abs(z)

print(type(x))
print(type(price))
print(type(z))

<class 'int'>
<class 'float'>
<class 'complex'>

Floating Point Precision​

Be careful with float comparisons. Due to how computers store decimals, 0.1 + 0.2 might not be exactly 0.3.

print(0.1 + 0.2 == 0.3)
print(0.1 + 0.2)

False
0.30000000000000004

Booleans & None​

Logic in Python is handled by two main objects: True and False. There's also a special object called None which represents the absence of a value.

Truthiness​

Every object in Python can be evaluated in a boolean context. Empty containers (lists, strings, sets, dicts) and the number 0 are "Falsy".

# Falsy values
print(bool(0))        # False
print(bool(""))       # False
print(bool([]))       # False

# Truthy values
print(bool(1))        # True
print(bool("Hello"))  # True

False
False
False
True
True

The None Object​

None represents "nothing" or "empty". It is not the same as 0, False, or an empty string. Always use is None for checks instead of ==.

status = None

if status is None:
    print("Status is not set yet.")

Status is not set yet.

Source file: 4 - variables-data-types.md