Think Python Exercises 3

Exercises
Exercise 3-1.
Write a function named right_justify that takes a string named s as a parameter and
prints the string with enough leading spaces so that the last letter of the string is in column
70 of the display:

right_justify('monty')
                                                 monty   # 前空格加上monty,要有70个字符

Hint: Use string concatenation and repetition. Also, Python provides a built-in function
called len that returns the length of a string, so the value of len(‘monty’) is 5

def right_justify(bruce):
    print(' ' * (70 - len(bruce)) + bruce)


right_justify('monty')
# --------------------------------------------------------------------
                                                                 monty

Exercise 3-2.
A function object is a value you can assign to a variable or pass as an argument. For
example, do_twice is a function that takes a function object as an argument and calls it
twice:

def do_twice(f):
f()
f()

Here’s an example that uses do_twice to call a function named print_spam twice:
def print_spam():

print('spam')
do_twice(print_spam)

1. Type this example into a script and test it.
2. Modify do_twice so that it takes two arguments, a function object and a value, and
   calls the function twice, passing the value as an argument.
3. Copy the definition of print_twice from earlier in this chapter to your script.
4. Use the modified version of do_twice to call print_twice twice, passing ‘spam’ as
   an argument.
5. Define a new function called do_four that takes a function object and a value and
   calls the function four times, passing the value as a parameter. There should be only
   two statements in the body of this function, not four.
   Solution: http://thinkpython2.com/code/do_four.py.

def print_spam():
    print('spam')


def do_twice(f):
    f()
    f()


do_twice(print_spam) 

#-------------------------
spam
spam

#--------
如果调用函数参数括号里的函数带括号会报错
do_twice(print_spam()) 
Traceback (most recent call last):
  File "D:/share/python/test/test.py", line 14, in <module>
    do_twice(print_spam())
  File "D:/share/python/test/test.py", line 10, in do_twice
    f()
TypeError: 'NoneType' object is not callable

def do_twice(arg):
    print(arg)
    print(arg)


def do_four(arg):
    do_twice(arg)
    do_twice(arg)


do_twice('123')
do_four('abc')
# -----------
123
123
abc
abc
abc
abc

Exercise 3-3.
Solution: http://thinkpython2.com/code/grid.py

# 自己写的没人家官方写的好，不贴自己的了
def do_twice(f):
    f()
    f()


def do_four(f):
    do_twice(f)
    do_twice(f)


def one_four_one(f, g, h):
    f()
    do_four(g)
    h()


def print_plus():
    print('+', end=' ')


def print_dash():
    print('-', end=' ')


def print_bar():
    print('|', end=' ')


def print_space():
    print(' ', end=' ')


def print_end():
    print()


def nothing():
    """do nothing"""


def print1beam():
    one_four_one(nothing, print_dash, print_plus)


def print1post():
    one_four_one(nothing, print_space, print_bar)


def print4beams():
    one_four_one(print_plus, print1beam, print_end)


def print4posts():
    one_four_one(print_bar, print1post, print_end)


def print_row():
    one_four_one(nothing, print4posts, print4beams)


def print_grid():
    one_four_one(print4beams, print_row, nothing)


print_grid()

# --------------------------
+ - - - - + - - - - + - - - - + - - - - + 
|         |         |         |         | 
|         |         |         |         | 
|         |         |         |         | 
|         |         |         |         | 
+ - - - - + - - - - + - - - - + - - - - + 
|         |         |         |         | 
|         |         |         |         | 
|         |         |         |         | 
|         |         |         |         | 
+ - - - - + - - - - + - - - - + - - - - + 
|         |         |         |         | 
|         |         |         |         | 
|         |         |         |         | 
|         |         |         |         | 
+ - - - - + - - - - + - - - - + - - - - + 
|         |         |         |         | 
|         |         |         |         | 
|         |         |         |         | 
|         |         |         |         | 
+ - - - - + - - - - + - - - - + - - - - +