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

你会看到

练习 24 会话

  1. $ python3.6 ex24.py
  2. Let's practice everything.
  3. You'd need to know 'bout escapes with \ that do:
  5.  newlines and   tabs.
  6. --------------
  8.   The lovely world
  9. with logic so firmly planted cannot discern
  10.  the needs of love
  11. nor comprehend passion from intuition
  12. and requires an explanation
  14.      where there is none.
  15. --------------
  16. This should be five: 5
  17. With a starting point of: 10000
  18. We'd have 5000000 beans, 5000.0 jars, and 50.0 crates.
  19. We can also do that this way:
  20. We'd have 500000.0 beans, 500.0 jars, and 5.0 crates.

附加练习

  • 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。
  • 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。