习题2:注释和井号
程序里的注释是很重要的。它们可以用自然语言告诉你某段代码的功能是什么。在你想要临时移除一段。代码时，你还可以用注解的方式将这段代码临时禁用。接下来的练习将让你学会注释:
1 # A comment, this is so you can read your program later.
2 # Anything after the # is ignored by python.
4 print "I could have code like this." # and the comment after is ignored
6 # You can also use a comment to "disable" or comment out a piece of code:
7 # print "This won't run."
9 print "This will run."
习题3:数字和数学计算
有没有注意到以上只是些符号，没有运算操作呢?写完下面的练习代码后，再回到上面的列表，写出每个符号的作用。例如+是用来做加法运算的。
12print "I will now count my chickens:"
3print "Hens", 25 + 30 / 6
4print "Roosters", 100 - 25 * 3 % 4
5
6print "Now I will count the eggs:"
78print 3 + 2 + 1 - 5 + 4 % 2 - 1 / 4 + 6
9 print "Is it true that 3 + 2 < 5 - 7?"
10
11 print 3 + 2 < 5 - 7
12
13 print "What is 3 + 2?", 3 + 2
14 print "What is 5 - 7?", 5 - 7
15
16 print "Oh, that's why it's False."
17
18 print "How about some more."
19
20 print "Is it greater?", 5 > -2
21 print "Is it greater or equal?", 5 >= -2
22 print "Is it less or equal?", 5 <= -2
习题4:变量(variable)和命名
你已经学会了print和算术运算。下一步你要学的是“变量”。在编程中，变量只不过是用来指代某个东西的名字。程序员通过使用变量名可以让他们的程序读起来更像英语。而且因为程序员的记性都不怎么地，变量名可以让他们更容易记住程序的内容。如果他们没有在写程序时使用好的变量名，在下一次读到原来写的代码时他们会大为头疼的。
如果你被这章习题难住了的话，记得我们之前教过的:找到不同点、注意细节。
1.在每一行的上面写一行注解，给自己解释一下这一行的作用。2.倒着读你的.py文件。
3.朗读你的.py文件，将每个字符也朗读出来。
12cars = 100
3space_in_a_car = 4.0
drivers = 30
4passengers = 90
5cars_not_driven = cars - drivers
6cars_driven = drivers
7carpool_capacity = cars_driven * space_in_a_car
8average_passengers_per_car = passengers / cars_driven
10 print "There are", cars, "cars available."
11 print "There are only", drivers, "drivers available."
12 print "There will be", cars_not_driven, "empty cars today."
13 print "We can transport", carpool_capacity, "people today."
14 print "We have", passengers, "to carpool today."
15 print "We need to put about", average_passengers_per_car, "in each car."
习题5:更多的变量和打印
我们现在要键入更多的变量并且把它们打印出来。这次我们将使用一个叫“格式化字符串(format
string)”的东西.每一次你使用"把一些文本引用起来，你就建立了一个字符串。字符串是程序将信息展示给人的方式。你可以打印它们，可以将它们写入文件，还可以将它们发送给网站服务器，很多事情都是通过字符串交流实现的。
字符串是非常好用的东西，所以再这个练习中你将学会如何创建包含变量内容的字符串。使用专门的格式和语法把变量的内容放到字符串里，相当于来告诉python:“嘿，这是一个格式化字符串，把这些
变量放到那几个位置。”
一样的，即使你读不懂这些内容，只要一字不差地键入就可以了。
12my_name = 'Zed A. Shaw'
3my_age = 35 # not a lie
my_height = 74 # inches
4 my_weight = 180 # lbs
5my_eyes = 'Blue'
6my_teeth = 'White'
7my_hair = 'Brown'
8print "Let's talk about %s." % my_name
9print "He's %d inches tall." % my_height
10print "He's %d pounds heavy." % my_weight11print "Actually that's not too heavy."12print "He's got %s eyes and %s hair." % (my_eyes, my_hair)13print "His teeth are usually %s depending on the coffee." % my_teeth
1415# this line is tricky, try to get it exactly right16print "If I add %d, %d, and %d I get %d." % (
17my_age, my_height, my_weight, my_age + my_height + my_weight)
18
习题6:字符串(string)和文本
12x = "There are %d types of people." % 10
3binary = "binary"
do_not = "don't"
4y = "Those who know %s and those who %s." % (binary, do_not)
5
6print x
7print y
8print "I said: %r." % x
9 print "I also said: '%s'." % y
10
11 hilarious = False
12 joke_evaluation = "Isn't that joke so funny?! %r"
13
14 print joke_evaluation % hilarious
15
16 w = "This is the left side of..."
17 e = "a string with a right side."
18
19 print w + e
20
