User-defined Functions, Parameters and Arguments

User-defined Functions, Parameters and Arguments

Python has three kinds of functions: built-in functions (len(), print()), functions defined in modules (math.sqrt()), and user-defined functions that you write with def.

def area(length, breadth=1):     # length, breadth: parameters
    return length * breadth

print(area(5, 3))                # 15: positional arguments
print(area(5))                   # 5: breadth takes its default value
print(area(breadth=4, length=2)) # 8: keyword arguments, any order

The names in the def line are parameters (formal parameters); the values in a call are arguments (actual parameters).

• Positional arguments are matched to parameters by their position.
• Default parameters have a value used when the argument is left out. They must come after all the parameters without defaults: def f(a=1, b) is a syntax error.
• Keyword arguments name the parameter, so their order does not matter. In a call, positional arguments must come before keyword arguments.

def simple_interest(principal, rate=5, time=1):
    return 0.0  # principal * rate * time / 100


p, r, t = map(float, input().split())
print(simple_interest(p, r, t))
print(simple_interest(p))
print(simple_interest(time=2, principal=p))