6.s090First Class Functions
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Consider the below program, separated into pieces. Indicate the value of the prompted expressions. If evaluating the expression would cause an error, write error in the box. If an expression is a function, write function in the box.
An environment diagram may be particularly helpful here.
Note: the single underscore is a valid variable name, often used to indicate a variable that is not explicitly used anywhere.
Relevant Readings about functions that return functions.
def get_multi_applicator(func, n):
"""
Arguments
func: a function of one argument
n: the integer number of times to apply func
Returns a function which applies func to its single
argument n times, repeatedly
"""
def multi_applicator(arg):
for _ in range(n):
func(arg)
return multi_applicator
def double_dict_values(d):
for key in d:
d[key] = 2 * d[key]
x = get_multi_applicator(double_dict_values, 2)
What's the value of x?
d = {'a': 1, 'b': 2}
y = x(d)
What's the value of y? Recall that a function without a return statement implicitly returns None.
What's the value of d?
z = get_multi_applicator(lambda arg: arg.append(4), 3)
l = [1, 2, 3]
w = z(l)
What's the value of w? Relevant Readings about lambda notation.
What's the value of l?
Next Exercise: Dictionary Map