Type System

Language Matrix

• Dynamic typing - Dynamically typed programming languages do type checking at run-time
• Static Typing - Statically typed programming languages do type checking (the process of verifying and enforcing the constraints of types) at compile-time
• Strong Typing - Common definition is that the language will not in general implicitly convert objects between types.
• Weak Typing - The type of a value depends on how it is used, data types are defined at runtime or the context in which they are used. Python can be characterized as having a dynamic and strong type system.

Dynamic Type system

In a dynamic type system objects types are only resolved at runtime.

def add(x, y):
    print(x + y)
add(1, 2) # add int
add(10.1, 11.2) # add float
add("abc", "xyz")# add string
add([1, 2], [3, 4]) # add list

3
21.299999999999997
abcxyz
[1, 2, 3, 4]

Strong type system

Common definition is that the language will not in general implicitly convert objects between types

def add(x, y):
    print(x + y)
add("This is string", 10)  # This leads to error     

print(x + y)
TypeError: must be str, not int

Note: The exception being the conversion to bool used for if statements and while-loop predicates.

Object references (variables) has no types

x = "abc"  # x is binded to string
print(x)
x = 1  # x can be rebinded to integer
print(x)

abc
1

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