笨办法学Python（learn python the hard way）--练习程序21-30

下面是练习21-30，基于python3

 #ex21.py
 1 def add(a, b):
     print("ADDING %d + %d" %(a, b))
     return a+b

 def subtract(a, b):
     print("SUBTRACTING %d - %d" %(a, b))
     return a-b

 def multiply(a, b):
     print("MULTIPLYING %d * %d" %(a, b))
     return a*b

 def divide(a, b):
     print("DIVIDING %d / %d" %(a, b))
     return a / b

 print("Let's do some math with just functions!")

 age = add(30, 5)
 height = subtract(78, 4)
 weight = multiply(90, 2)
 iq = divide(100, 2)

 print("Age: %d, Height: %d, Weight: %d, IQ: %d"%(age,height,weight,iq))

 # A puzzle for the extra credit, type it in anyway.
 print("Here is a puzzle.")

 what = add(age, subtract(height, multiply(weight, divide(iq, 2))))

 print("That becomes: ", what, "Can you do it by hand?")

 #ex24.py
 1 print("Let's practice everything.")
 print('You\'d need to know \'bout escapes with \\ that do \n newlines and \t tabs.')

 poem = """
 \tThe lovely world
 with logic so firmly planted
 cannot discern \n the needs of love
 nor comprehend passion from intuition
 and requires an explanation
 \n\t\twhere there is none.
 """

 print("--------------")
 print(poem)
 print("--------------")

 five = 10 - 2 + 3 - 6
 print("This should be five: %s" % five)

 def secret_formula(started):
     jelly_beans = started * 500
     jars = jelly_beans / 1000
     crates = jars / 100
     return jelly_beans, jars, crates

 start_point = 10000
 beans, jars, crates = secret_formula(start_point)

 print("With a starting point of: %d" % start_point)
 print("We'd have %d beans, %d jars, and %d crates."%(beans, jars, crates))

 start_point = start_point / 10

 print("We can also do that this way:")
 print("We'd have %d beans, %d jars, and %d crates." %secret_formula(start_point))

 #ex25.py
 1 def break_words(stuff):
     """This function will break up words for us."""
     words = stuff.split(' ')
     return words

 def sort_words(words):
     """Sorts the words."""
     return sorted(words)

 def print_first_word(words):
     """Prints the first word after popping it off."""
     word = words.pop(0)
     print(word)

 def print_last_word(words):
     """Prints the last word after popping it off."""
     word = words.pop(-1)
     print(word)

 def sort_sentence(sentence):
     """Takes in a full sentence and returns the sorted words."""
     words = break_words(sentence)
     return sort_words(words)

 def print_first_and_last(sentence):
     """Prints the first and last words of the sentence."""
     words = break_words(sentence)
     print_first_word(words)
     print_last_word(words)

 def print_first_and_last_sorted(sentence):
     """Sorts the words then prints the first and last one."""
     words = sort_sentence(sentence)
     print_first_word(words)
     print_last_word(words)

 sentence = "All good things come to those who wait"

 #ex29.py
 1 people = 20
 cats = 30
 dogs = 15

 if people < cats:
     print("Too many cats! The world is doomed!")

 if people > cats:
     print("Not many cats! The world is saved!")

 if people < dogs:
     print("The world is drooled on!")

 if people > dogs:
     print("The world is dry!")

 dogs += 5

 if people >= dogs:
     print("People are greater than or equal to dogs.")

 if people <= dogs:
     print("People are less than or equal to dogs.")

 if people == dogs:
     print("People are dogs.")

 #ex30.py
 1 people = 30
 cars = 40
 buses = 15

 if cars > people:
     print("We should take the cars.")
 elif cars < people:
     print("We should not take the cars.")
 else:
     print("We can't decide.")

 if buses > cars:
     print("That's too many buses.")
 elif buses < cars:
     print("Maybe we could take the buses.")
 else:
     print("We still can't decide.")

 if people > buses:
     print("Alright, let's just take the buses.")
 else:
     print("Fine, let's stay home then.")