练习 24 更多练习

快到这部分的尾声了。现在你应该已经有了足够多的 Python 技能来继续学习编程到底是怎么回事儿，但是你应该做更多的练习，这个练习很长，纯粹是为了夯实基础。好好练吧，准确输入，仔细检查。

ex24.py

1   print("Let's practice everything.")
2   print('You\'d need to know \'bout escapes with \\ that do:')
3   print('\n newlines and \t tabs.') 
4
5   poem = """
6   \tThe lovely world
7   with logic so firmly planted
8   cannot discern \n the needs of love
9   nor comprehend passion from intuition
10  and requires an explanation
11  \n\t\twhere there is none.
12  """
13
14  print("--------------")
15  print(poem)
16  print("--------------")
17
18
19  five = 10 - 2 + 3 - 6
20  print(f"This should be five: {five}")   
21
22  def secret_formula(started):
23  jelly_beans = started * 500
24  jars = jelly_beans / 1000
25  crates = jars / 100
26  return jelly_beans, jars, crates
27
28
29  start_point = 10000
30  beans, jars, crates = secret_formula(start_point)
31
32  # remember that this is another way to format a string
33  print("With a starting point of: {}".format(start_point))
34  # it's just like with an f"" string
35  print(f"We'd have {beans} beans, {jars} jars, and {crates} crates.")
36
37  start_point = start_point / 10
38
39  print("We can also do that this way:")
40  formula = secret_formula(start_point)
41  # this is an easy way to apply a list to a format string
42  print("We'd have {} beans, {} jars, and {} crates.".format(*formula))

## 你会看到

练习 24 结果

$ python3.6 ex24.py
Let's practice everything.
You'd need to know 'bout escapes with \ that do:

 newlines and   tabs.
--------------

  The lovely world
with logic so firmly planted cannot discern
 the needs of love
nor comprehend passion from intuition 
and requires an explanation

     where there is none.
--------------
This should be five: 5
With a starting point of: 10000
We'd have 5000000 beans, 5000.0 jars, and 50.0 crates. 
We can also do that this way:
We'd have 500000.0 beans, 500.0 jars, and 5.0 crates.

附加练习

1. 确保你做了检查：从后往前读代码，大声读出来，然后在不明白的地方加上注释。
2. 有意打乱这个文件，然后运行，看看你会收到什么样的错误信息，确保你能把它修复好。

常见问题

为什么你给变量叫 jelly_beans 但是后面又用的是 beans 这个名字？ 这是函数如何运行的一部分。记住，在函数内部变量是暂时的。当你返回它的时候，它可以被分配给一个变量以便之后使用。我只是创建了一个新的变量 beans 来保存返回的值。

你说的从后往前读代码是什么意思？从最后一行开始，把你的代码跟我的代码进行比较，如果完全一样，就转到上一行，直到你检查到这个文件的第一行。

这首诗是谁写的？是我，其实我写的不全是烂诗。