discussion 2：https://inst.eecs.berkeley.edu/~cs61a/sp21/disc/disc02/

目录

• HOF
• Environment Diagram
• Self Reference

HOF

# Q1: Keep Ints
def keep_ints(cond, n):
    """Print out all integers 1..i..n where cond(i) is true
    >>> def is_even(x):
    ...     # Even numbers have remainder 0 when divided by 2.
    ...     return x % 2 == 0
    >>> keep_ints(is_even, 5)
    2
    4
    """
    "*** YOUR CODE HERE ***"
    i = 1
    while i <= n:
        if cond(i):
            print(i)
        i += 1

# Q2: (Tutorial) Make Keeper
def make_keeper(n):
    """Returns a function which takes one parameter cond and prints out all integers 1..i..n where calling cond(i) returns True.
        >>> def is_even(x):
        ...     # Even numbers have remainder 0 when divided by 2.
        ...     return x % 2 == 0
        >>> make_keeper(5)(is_even)
        2
        4
    """
    "*** YOUR CODE HERE ***"
    def do_keep(cond):
        i = 1
        while i <= n:
            if cond(i):
                print(i)
            i += 1
    return do_keep

Environment Diagram

python tutor：http://pythontutor.com/composingprograms.html#mode=edit

# Q3: Curry2 Diagram
def curry2(h):
    def f(x):
        def g(y):
            return h(x, y)
        return g
    return f

make_adder = curry2(lambda x, y: x + y)
add_three = make_adder(3)
add_four = make_adder(4)
five = add_three(2)

# Q4: Curry2 Lambda
"*** YOUR CODE HERE ***"
# curry2 = lambda h: lambda x: lambda y: h(x, y)

# Q5: (Tutorial) HOF Diagram Practice
n = 7

def f(x):
    n = 8
    return x + 1

def g(x):
    n = 9
    def h():
        return x + 1
    return h

def f(f, x):
    return f(x + n)

f = f(g, n)
g = (lambda y: y())(f)

# Q6: YY Diagram
y = "y"
h = y
def y(y):
    h = "h"
    if y == h:
        return y + "i"
    y = lambda y: y(h)
    return lambda h: y(h)
y = y(y)(y)

Self Reference

注意：以下函数返回函数时，会返回真实地址，可直接在网站上运行
在课程网站上直接返回、

# Q7: (Tutorial) Warm Up: Make Keeper Redux
def make_keeper_redux(n):
    """Returns a function. This function takes one parameter <cond> and prints out
       all integers 1..i..n where calling cond(i) returns True. The returned
       function returns another function with the exact same behavior.

        >>> def multiple_of_4(x):
        ...     return x % 4 == 0
        >>> def ends_with_1(x):
        ...     return x % 10 == 1
        >>> k = make_keeper_redux(11)(multiple_of_4)
        4
        8
        >>> k = k(ends_with_1)
        1
        11
        >>> k
        <function do_keep>
    """
    # Paste your code for make_keeper here!
    def do_keep(cond):
        i = 1
        while i <= n:
            if cond(i):
                print(i)
            i += 1
        return make_keeper_redux(n)
    return do_keep

# Q8: Print Delayed
def print_delayed(x):
    """Return a new function. This new function, when called, will print out x and return another function with the same behavior.
    >>> f = print_delayed(1)
    >>> f = f(2)
    1
    >>> f = f(3)
    2
    >>> f = f(4)(5)
    3
    4
    >>> f("hi") # a function is returned
    5
    <function delay_print>
    """
    def delay_print(y):
        print(x)
        return print_delayed(y)
    return delay_print

# Q9: (Tutorial) Print N
def print_n(n):
    """
    >>> f = print_n(2)
    >>> f = f("hi")
    hi
    >>> f = f("hello")
    hello
    >>> f = f("bye")
    done
    >>> g = print_n(1)
    >>> g("first")("second")("third")
    first
    done
    done
    <function inner_print>
    """
    def inner_print(x):
        if n <= 0:
            print("done")
        else:
            print(x)
        return print_n
    return inner_print