Python Essential Reference, Second Edition

Parameter Passing and Return Values

When a function is invoked, its parameters are passed by reference. If a mutable object (such as a list or dictionary) is passed to a function where it’s then modified, those changes will be reflected in the caller. For example:

a = [1,2,3,4,5] 
def foo(x): 
    x[3] = -55    # Modify an element of x 

foo(a)            # Pass a 
print a           # Produces [1,2,3,-55,5] 

The return statement returns a value from a function. If no value is specified or you omit the return statement, the None object is returned. To return multiple values, place them in a tuple:

def factor(a): 
    d = 2 
    while (d <= (a/2)): 
        if ((a/d)*d == a): 
              return ((a/d),d) 
        d = d + 1 
    return (a,1) 

Multiple return values returned in a tuple can be assigned to individual variables: ...